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DS1923
Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
www.maxim-ic.com
SPECIAL FEATURES
Digital Hygrometer Measures Humidity with 8-Bit (0.6%RH) or 12-Bit (0.04%RH) Resolution Operating Range: -20 to +85C; 0 to 100%RH (see Safe Operating Range) Automatically Wakes Up, Measures Temperature and/or Humidity and Stores Values in 8kB of Datalog Memory in 8- or 16-Bit Format Digital Thermometer Measures Temperature with 8-Bit (0.5C) or 11-Bit (0.0625C) Resolution Temperature Accuracy Better than 0.5C from -10C to +65C with Software Correction Built-in Humidity Sensor for Simultaneous Temperature and Humidity Logging Capacitive Polymer Humidity-Sensing Element Hydrophobic Filter Protects Sensor Against Dust, Dirt, Water, and Contaminants Sampling Rate from 1s up to 273hrs Programmable Recording Start Delay After Elapsed Time or Upon a Temperature Alarm Trip Point Programmable High and Low Trip Points for Temperature and Humidity Alarms Quick Access to Alarmed Devices Through 1-WireO Conditional Search Function 512 Bytes of General-Purpose Memory Plus 64 Bytes of Calibration Memory Two-Level Password Protection of All Memory and Configuration Registers Communicates to Host with a Single Digital Signal at Up to 15.4kbps at Standard Speed or Up to 125kbps in Overdrive Mode Using 1-Wire Protocol Individually Calibrated in a NIST-Traceable Chamber Calibration Coefficients for Temperature and Humidity Factory Programmed into Nonvolatile (NV) Memory Temperature and Humidity Logging in Food Preparation and Processing Transportation of Temperature- and HumiditySensitive Goods, Industrial Production Warehouse Monitoring Environmental Studies/Monitoring PART DS1923-F5 TEMP RANGE -20C to +85C PACKAGE F5 iButton
iButton DESCRIPTION
The DS1923 temperature/humidity logger iButton is a rugged, self-sufficient system that measures temperature and/or humidity and records the result in a protected memory section. The recording is done at a user-defined rate. A total of 8192 8-bit readings or 4096 16-bit readings taken at equidistant intervals ranging from 1s to 273hrs can be stored. In addition to this, there are 512 bytes of SRAM for storing application-specific information and 64 bytes for calibration data. A mission to collect data can be programmed to begin immediately, or after a userdefined delay or after a temperature alarm. Access to the memory and control functions can be passwordprotected. The DS1923 is configured and communicates with a host-computing device through the serial 1-Wire protocol, which requires only a single data lead and a ground return. Every DS1923 is factory-lasered with a guaranteed unique 64-bit registration number that allows for absolute traceability. The durable stainless-steel package is highly resistant to environmental hazards such as dirt, moisture, and shock. Accessories permit the DS1923 to be mounted on almost any object, including containers, pallets and bags.
F5 MICROCAN
5.89 0.51
a
16.25 17.35
APPLICATIONS

IO GND Front Side Brand
a
All dimensions are shown in millimeters.
A1
ORDERING INFORMATION
000000FBC52B
HygrochronTM
a
41
1-Wirea
1-Wire and iButton are registered trademarks of Dallas Semiconductor. Hygrochron is a trademark of Dallas Semiconductor.
Back Side Brand
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REV: 110504
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data log Memory
DS1923 ABSOLUTE MAXIMUM RATINGS
IO Voltage to GND IO Sink current Operating Temperature and Humidity Range Storage Temperature and Humidity Range -0.3V, +6V 20mA -20C to +85C, 0%RH to 100%RH (See Safe Operating Range Chart) -40C to +85C, 0%RH to 100%RH (See Safe Operating Range Chart)
This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
DS1923 ELECTRICAL CHARACTERISTICS (VPUP = 3.0V to 5.25V, TA = -20C to +85C)
PARAMETER IO Pin General Data 1-Wire Pullup Resistance Input Capacitance Input Load Current High-to-Low Switching Threshold Input Low Voltage Low-to-High Switching Threshold Switching Hysteresis Output Low Voltage Recovery Time (Note 1) Rising-Edge Hold-off Time Timeslot Duration (Note 1) SYMBOL RPUP CIO IL VTL VIL VTH VHY VOL tREC CONDITIONS MIN TYP MAX 2.2 100 6 0.4 0.7 0.09 5 2 5 0.6 65 8 9.5 480 690 48 70 15 15 2 1.5 1.5 0.15 60 60 7 7 65 71.5 8 720 720 80 80 60 63.5 7 5 8 1 240 287 24 28 75 75 9 2.0 s s 800 10 3.2 0.3 3.4 N/A 0.4 UNITS kW pF A V V V V V s (Notes 1, 2) (Note 3) IO pin at VPUP (Notes 4. 5) (Notes 1, 6) (Notes 4, 7) (Note 8) At 4mA (Note 9) Standard speed, RPUP = 2.2kW Overdrive speed, RPUP = 2.2kW Overdrive speed, directly prior to reset pulse; RPUP = 2.2kW (Note 10)
tREH tSLOT
Standard speed Overdrive speed, VPUP > 4.5V Overdrive speed (Note 11) IO Pin, 1-Wire Reset, Presence Detect Cycle Standard speed, VPUP > 4.5V Reset Low Time Standard speed (Note 11) tRSTL (Note 1) Overdrive speed, VPUP > 4.5V Overdrive speed (Note 11) Standard speed, VPUP > 4.5V Presence-Detect High tPDH Standard speed (Note 11) Time Overdrive speed (Note 11) Standard speed, VPUP > 4.5V Presence-Detect Fall Time tFPD Standard speed (Note 12) Overdrive speed Standard speed, VPUP > 4.5V Standard speed (Note 11) Presence-Detect Low tPDL Overdrive speed, VPUP > 4.5V Time (Note 11) Overdrive speed (Note 11) Standard speed, VPUP > 4.5V Presence-Detect Sample Time tMSP Standard speed (Note 1) Overdrive speed
s
s s
s
s
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PARAMETER IO Pin, 1-Wire Write Write-0 Low Time (Note 1) Write-1 Low Time (Notes 1, 13) IO Pin, 1-Wire Read Read Low Time (Notes 1, 14) Read Sample Time (Notes 1, 14) Real-Time Clock Accuracy Frequency Deviation Temperature Converter Conversion Time
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory SYMBOL CONDITIONS MIN TYP MAX UNITS Standard speed Overdrive speed, VPUP > 4.5V (Note 11) Overdrive speed (Note 11) Standard speed Overdrive speed Standard speed Overdrive speed Standard speed Overdrive speed +25C DF tCONV -20C to +85C 8-bit mode (Note 15) 16-bit mode (11 bits) iButton package (Note 16) (Notes 15, 17, 18, 19) (Notes 15, 17, 18, 19) Slow moving air (Note 20) (Note 21) (Note 22) With software correction (Notes 18, 19, 23, 24, 25) With software correction (Note 18) (Notes 26, 27) (Note 28) At 50%RH (Note 29) 8 0.64 0 60 6 7.5 5 1 5 1 tRL + d tRL + d -3 -300 30 240 130 See Temperature Accuracy Graphs See Temperature Accuracy Graphs 30 12 0.04 5 <1 0.5 0.5 <1.0 12 0.04 100 120 12 12 15 - e 1.95 - e 15 - d 1.95 - d 15 1.95 +3 +60 75 600 s
tW0L tW1L
s
tRL tMSR
s s min./ month PPM ms s C C s bits %RH %RH %RH %RH %RH %RH/y
Thermal Response tRESP Time Constant Conversion Error Without Software DJ Correction Conversion Error With DJ Software Correction Humidity Converter (Note 30) Humidity Response tRH Time Constant RH Resolution RH Range RH Accuracy and Interchangeability RH Nonlinearity RH Hysteresis RH Repeatability Long-Term Stability
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16:
System requirement. Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For more heavily loaded systems, an active pullup such as that found in the DS2480B may be required. Capacitance on the data pin could be 800pF when VPUP is first applied. If a 2.2kW resistor is used to pull up the data line 2.5s after VPUP has been applied, the parasite capacitance does not affect normal communications. VTL, VTH are a function of the internal supply voltage. Voltage below which, during a falling edge on IO, a logic '0' is detected. The voltage on IO needs to be less or equal to VILMAX whenever the master drives the line low. Voltage above which, during a rising edge on IO, a logic '1' is detected. After VTH is crossed during a rising edge on IO, the voltage on IO has to drop by VHY to be detected as logic '0'. The I-V characteristic is linear for voltages less than 1V. The earliest recognition of a negative edge is possible at tREH after VTH has been previously reached. Highlighted numbers are NOT in compliance with the published iButton standards. See comparison table below. Interval during the negative edge on IO at the beginning of a presence detect pulse between the time at which the voltage is 90% of VPUP and the time at which the voltage is 10% of VPUP. e represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. d represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus master. To conserve battery power, use 8-bit temperature logging whenever possible. This number was derived from a test conducted by Cemagref in Antony, France, in July of 2000. http://www.cemagref.fr/English/index.htm Test Report No. E42.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Note 17: Note 18: Note 19: For software corrected accuracy, assume correction using calibration coefficients with calibration equations for error compensation. Software correction for humidity and temperature is handled automatically using the 1-Wire Viewer Software package available at: http://www.ibutton.com. WARNING: Not for use as the sole method of measuring or tracking temperature and/or humidity in products and articles that could affect the health or safety of persons, plants, animals, or other living organisms, including but not limited to foods, beverages, pharmaceuticals, medications, blood and blood products, organs, flammable, and combustible products. User shall assure that redundant (or other primary) methods of testing and determining the handling methods, quality, and fitness of the articles and products should be implemented. Temperature and/or humidity tracking with this product, where the health or safety of the aforementioned persons or things could be adversely affected, is only recommended when supplemental or redundant information sources are used. Data logger products are 100% tested and calibrated at time of manufacture by Dallas Semiconductor/Maxim to ensure that they meet all data sheet parameters, including temperature accuracy. User shall be responsible for proper use and storage of this product. As with any sensor-based product, user shall also be responsible for occasionally rechecking the temperature accuracy of the product to ensure it is still operating properly. Response time is determined by measuring the 1/e point as the device transitions from 40 to 90%RH or 90 to 40%RH, whichever is slower. Test was performed at 5L/min airflow. All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery lifetime is the same no matter what RH resolution is logged. Reliability studies have shown that the device survives a minimum of 1000 cycles of condensation and drying, but this product is not guaranteed for extended use in condensing environments. Software corrected accuracy is accomplished using the method detailed in the Software Correction Algorithm for Temperature section of this data sheet. Every DS1923 Device is measured and calibrated in a controlled, NIST-traceable RH environment. Higher accuracy versions may be available. Contact the factory for details. If this device is exposed to a high humidity environment (>70%RH), and then exposed to a lower RH environment, the device will read high for a period of time. The device will typically read within +0.5%RH at 20%RH, 30 minutes after being exposed to continuous 80%RH for 30 minutes. All capacitive RH sensors can change their reading depending upon how long they have spent at high (>70%RH) or low RH (<20%RH). This effect is called saturation drift and can be compensated through software, as described in the Software Saturation Drift Compensation section of this data sheet. Individual RH readings always include a noise component (repeatability). To minimize measurement error, average as many samples as is reasonable. Like all relative humidity sensors, when exposed to contaminants and/or conditions toward the limits of the safe operating range, accuracy degradation can result (see Safe Operating Range chart). For maximum long-term stability, the sensor should not be exposed or subjected to organic solvents, corrosive agents (strong acids, SO2, H2SO4, CI2 ,HCL, H2S, etc.) and strong bases (compounds with PH greater than 7). Dust settling on the filter surface does not affect the sensor performance except to possibly decrease the speed of response. For more information on the RH sensor's tolerance to chemicals visit: http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf All humidity specifications are determined at +25C except where specifically indicated.
Note 20: Note 21: Note 22: Note 23: Note 24: Note 25: Note 26: Note 27: Note 28: Note 29:
Note 30:
Parameter Name tSLOT (incl. tREC) tRSTL tPDH tPDL tW0L
1)
Standard Values Standard Speed Overdrive Speed Min Max Min Max 61s (undef.) 7s (undef.) 480s (undef.) 48s 80s 15s 60s 2s 6s 60s 240s 8s 24s 60s 120s 6s 16s
DS1923 Values Standard Speed Overdrive Speed Min Max Min Max 1) 65s (undef.) 9.5s (undef.) 690s 720s 70s 80s 15s 63.5s 2s 7s 60s 287s 7s 28s 60s 120s 7.5s 12s
Intentional change, longer recovery time requirement due to modified 1-Wire front end.
PHYSICAL SPECIFICATION
Size Weight Safety See mechanical drawing Ca. 5.0 grams th Meets UL#913 (4 Edit.); Intrinsically Safe Apparatus, approval under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations (application pending)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Safe Operating Range
100 Humidity (%RH) 80 60 40 20 0 -40 -20 0 20 40 60 80 Temperature (C)
Storage Only
Safe Operating Zone
DS1923 Temperature Accuracy
Uncorrected Max Error SW Corrected Max Error 2.0 1.5 Uncorrected Min Error SW Corrected Min Error
DS1923: Error (C)
1.0 0.5 0.0 -0.5 -1.0 -20 -10 0 10 20 30 40 50 60 70 80 Temperature (C)
NOTE: The graphs are based on 11-bit data.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Slow Sampling Temperature Only
Every Minute Every 60 Min.
8-Bit Min. Product Lifetime (years)
10 9 8 7 6 5 4 3 2 1 0 -20 -10 0 10 20 30 40 50 60 70 80
Every 3 Min. No Samples
Every 10 Min. Osc. Off
DS1923: Temperature (C)
Every Minute Every 30 Min. No Samples
Every 3 Min. Every 60 Min. Osc. Off
Every 10 Min. Every 300 Min.
11-Bit Min. Product Lifetime (years)
10 9 8 7 6 5 4 3 2 1 0 -20 -10 0 10 20 30 40 50 60 70 80
DS1923: Temperature (C)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Fast Sampling Temperature Only
Every Second Every 30 Sec.
8-Bit Min. Product Lifetime (days)
350 300 250 200 150 100 50 0 -20 -10 0 10 20 30 40 50 60 70 80
Every 3 Sec. Every 60 Sec.
Every 10 Sec.
DS1923: Temperature (C)
Every Second Every 30 Sec.
Every 3 Sec. Every 60 Sec.
Every 10 Sec.
11-Bit M in. Product Lifetime (days)
100 80 60 40 20 0 -20 -10 0 10 20 30 40 50 60 70 80
DS1923: Temperature (C)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Slow Sampling, Temperature with Humidity
Every Minute Every 60 Min.
10
Every 3 Min. No Samples
Every 10 Min. Osc. Off
8-Bit Temp. plus Humidity Min. Product Lifetime (years)
9 8 7 6 5 4 3 2 1 0 -20 -10 0 10 20 30 40 50 60 70 80
DS1923: Temperature (C)
Minimum Lifetime vs. Temperature, Fast Sampling, Temperature with Humidity
Every Second Every 30 Sec. Every 3 Sec. Every 60 Sec. Every 10 Sec.
8-Bit Temp. plus Humidity Min. Product Lifetime (days)
350 300 250 200 150 100 50 0 -20 -10 0 10 20 30 40 50 60 70 80
DS1923: Temperature (C)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Product Lifetime vs. Sample Rate (Temperature Only)
0C 40C 60C 75C 85C
8-Bit Min. Product Lifetime (years)
10
1
0.1
0.01 0.01
0.1
1
10
100
DS1923: Minutes between Samples
NOTE: With humidity logging activated, the lifetime is reduced by less than 11% for sample rate of 3 minutes and slower and by a maximum of 20% for sample rate of 1 minute and faster.
0C
40C
60C
75C
85C
11-Bit Min. Product Lifetime (years)
10
1
0.1
0.01
0.001 0.01
0.1
1
10
100
DS1923: Minutes between Samples
NOTE: With humidity logging activated, the lifetime is reduced by a maximum of 4%. The incremental energy consumed by humidity logging is independent of the humidity logging resolution.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
COMMON iButton FEATURES
Digital Identification and Information by Momentary Contact Unique Factory-Lasered 64-Bit Registration Number Assures Error-Free Device Selection and Absolute Traceability Because No Two Parts are Alike Built-in Multidrop Controller for 1-Wire Net Chip-Based Data Carrier Compactly Stores Information Data can be Accessed While Affixed to Object Button Shape is Self-Aligning with Cup-Shaped Probes Durable Stainless-Steel Case Engraved with Registration Number Withstands Harsh Environments Easily Affixed with Self-Stick Adhesive Backing, Latched by its Flange, or Locked with a Ring Pressed onto its Rim Presence Detector Acknowledges when Reader First Applies Voltage Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus: Approved Under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations (Application Pending)
EXAMPLES OF ACCESSORIES
DS9096P DS9101 DS9093RA DS9093A DS9092 Self-Stick Adhesive Pad Multipurpose Clip Mounting Lock Ring Snap-In Fob iButton Probe
APPLICATION
The DS1923 is an ideal device to monitor for extended periods of time the temperature and humidity of any object it is attached to or shipped with, such as fresh produce, medical drugs and supplies and for use in refrigerators and freezers, as well as for logging climatic data during the transport of sensitive objects and critical processes such as curing. A 1.27mm diameter hole in the lid of the device allows for air to reach the humidity sensor. The rest of the electronics inside the DS1923 is sealed so that it is not exposed to ambient humidity. Software for setup and data retrieval through the 1-Wire interface is available for free download from the iButton website (www.ibutton.com). This software also includes drivers for the serial and USB port of a PC, and routines to access the general-purpose memory for storing application- or equipment-specific data files.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of the DS1923. The device has six main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 512-byte general-purpose SRAM, 4) two 256-bit register pages of timekeeping, control, status, and counter registers and passwords, 5) 64 bytes of calibration memory, and 6) 8192 bytes of data-logging memory. Except for the ROM and the scratchpad, all other memory is arranged in a single linear address space. The data logging memory, counter registers and several other registers are read-only for the user. Both register pages are write-protected while the device is programmed for a mission. The password registers, one for a read password and another one for a read/write password can only be written to but never read. The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one of the eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5) Skip ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM, or 8) Resume. Upon completion of an Overdrive ROM command byte executed at standard speed, the device enters Overdrive mode, where all subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is described in Figure 11. After a ROM function command is successfully executed, the memory and control functions become accessible and the master can provide any one of the eight available commands. The protocol for these memory and control function commands is described in Figure 9. All data is read and written least significant bit first.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 1. DS1923 BLOCK DIAGRAM
ROM Function Control 64-Bit Lasered ROM Parasite Powered Circuitry
1-Wire Port
IO
3V Lithium
Memory Function Control
256-Bit Scratchpad
General-Purpose SRAM (512 Bytes)
DS1923
32.768 kHz Oscillator
Internal Timekeeping & Control Reg. & Counters
Register Pages (64 Bytes)
Thermal Sense
ADC1
Calibration Memory (64 Bytes)
Humidity Sensor and ADC2
Control Logic
Datalog Memory 8K Bytes
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry "steals" power whenever the IO input is high. IO provides sufficient power as long as the specified timing and voltage requirements are met. The advantages of parasite power are two-fold: 1) by parasiting off this input, battery power is conserved, and 2) if the battery is exhausted for any reason, the ROM may still be read.
64-BIT LASERED ROM
Each DS1923 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. See Figure 4 for details. The 1Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in 8 5 4 Figure 3. The polynomial is X + X + X + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is available in Dallas Application Note 27. The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, then the serial number followed by the temperature range code is entered. After the range code has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC returns the shift register to all 0s.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 2. HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL
BUS Master 1-Wire net Other Devices
DS1923 Command Level: Available Commands:
Read ROM Match ROM Search ROM Conditional Search ROM Skip ROM Resume Overdrive Skip Overdrive Match Write Scratchpad Read Scratchpad Copy Scratchpad w/PW Read Memory w/PW & w/CRC Clear Memory w/PW Forced Conversion Start Mission w/PW Stop Mission w/PW
Data Field Affected:
64-bit ROM, RC-Flag 64-bit ROM, RC-Flag 64-bit ROM, RC-Flag 64-bit ROM, RC-Flag, Alarm Flags, Search Conditions RC-Flag RC-Flag RC-Flag, OD-Flag 64-bit ROM, RC-Flag, OD-Flag 256-bit Scratchpad, Flags 256-bit Scratchpad 512 byte Data Memory, Registers, Flags, Passwords Memory, Registers, Passwords Mission Time Stamp, Mission Samples Counter, Start Delay, Alarm Flags, Passwords Memory addresses 020C to 020Fh Flags, Timestamp, Memory addresses 020C to 020Fh (when logging) Flags
1-Wire ROM Function Commands
DS1923-specific Memory Function Commands
Figure 3. 1-Wire CRC GENERATOR
Polynomial = X + X + X + 1
8 5 4
1 STAGE
st
2 STAGE
nd
3 STAGE
rd
4 STAGE
th
5 STAGE
th
6 STAGE
th
7 STAGE
th
8 STAGE
th
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
X
8
INPUT DATA
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 4. 64-BIT LASERED ROM
MSB 8-Bit CRC Code MSB LSB MSB 48-Bit Serial Number LSB LSB 8-Bit Family Code (41h) MSB LSB
MEMORY
The memory map of the DS1923 is shown in Figure 5. The 512 bytes general-purpose SRAM are located in pages 0 through 15. The various registers to set up and control the device fill page 16 and 17, called Register Pages 1 and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. The "data log" logging memory starts at address 1000h (page 128) and extends over 256 pages. The memory pages 20 to 127 are reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the SRAM memory or the register page. The data memory can be written at any time. The calibration memory holds data from the device calibration that can be used to further improve the accuracy of temperature and humidity readings. See the Software Correction Algorithm sections for details. The last byte of the calibration memory page stores an 8-bit CRC of the preceding 31 bytes. Page 19 is an exact copy of the data in page 18. While the user can overwrite the calibration memory, this is not recommended. See the Security by Password section for ways to protect the memory. The access type for the register pages is register-specific and depends on whether the device is programmed for a mission. Figure 6 shows the details. The data log memory is read-only for the user. It is written solely under supervision of the on-chip control logic. Due to the special behavior of the write access logic (write scratchpad, copy scratchpad) it is recommended to only write full pages at a time. This also applies to the register pages and the calibration memory. See the Address Register and Transfer Status section for details.
Figure 5. DS1923 MEMORY MAP
32-Byte Intermediate Storage Scratchpad ADDRESS 0000H to 001FH 0020H to 01FFH 0200H to 021FH 0220H to 023FH 0240H to 025FH 0260H to 027FH 0280H to 0FFFH 1000H to 2FFFH
32-Byte General-Purpose SRAM (R/W) General-Purpose SRAM (R/W) 32-Byte Register Page 1 32-Byte Register Page 2 Calibration Memory Page 1 (R/W) Calibration Memory Page 2 (R/W) (Reserved For Future Extensions) Data Log Memory (Read-Only)
Page 0 Pages 1 to 15 Page 16 Page 17 Page 18 Page 19 Pages 20 to 127 Pages 128 to 383
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 6. DS1923 REGISTER PAGES MAP
ADDR 0200h 0201h 0202h 0203h 0204h 0205h 0206h 0207h 0208h 0209h 020Ah 020Bh 020Ch 020Dh 020Eh 020Fh 0210h 0211h 0212h 0213h 0214h 0215h 0216h 0217h 0218h 0219h 021Ah 021Bh 021Ch 021Dh 021Eh 021Fh 0220h 0221h 0222h 0223h 0224h 0225h 0226h 0227h 0228h 3/4 022Fh 0230h 3/4 0237h 0238h 3/4 023Fh b7 0 0 0 0 CENT 0 b6 b5 10 Seconds 10 Minutes
20h. AM/PM
b4
b3
b2 b1 Single Seconds Single Minutes Single Hours
b0
Function RealTime Clock Registers Sample Rate Temp. Alarms Humidity Alarms Latest Temp. Latest Humidity T.Alm.En. H.Alm.En. RTC En. Mis. Cntrl. Alm. Stat. Gen. Stat. Start Delay Counter Mission Time Stamp (N/A) Mission Sample Counter Device Sample Counter Flavor PW. Cntrl. Read Access Password Full Access Password (N/A)
Access*
12/24
10h.
R/W; R
0 1 0 1 BOR 1
0 0 0 0 CENT
0 10 Date Single Date 0 0 10m. Single Months 10 Years Single Years Low Byte 0 High Byte Low Threshold High Threshold Low Threshold High Threshold Low Byte 0 0 0 0 High Byte Low Byte High Byte 0 0 0 0 0 ETHA 1 1 1 1 1 EHHA 0 0 0 0 0 EHSS 1 SUTA RO HLFS TLFS EHL 1 1 1 HHF HLF THF 1 0 WFTA MEMCLR 0 MIP Low Byte Center Byte High Byte 10 Seconds Single Seconds 10 Minutes Single Minutes 12/24
20h. AM/PM
R/W; R R/W; R R/W; R R; R R; R R/W; R R/W; R R/W; R R/W; R R; R R; R R/W; R
0
ETLA EHLA EOSC ETL TLF 0
10h.
Single Hours
R; R
0 10 Date Single Date 0 0 10m. Single Months 10 Years Single Years (No Function; Reads 00h) Low Byte Center Byte High Byte Low Byte Center Byte High Byte Configuration Code EPW First Byte 3/4 Eighth Byte First Byte 3/4 Eighth Byte (No Function; All of These Bytes Read 00h)
R; R R; R R; R R; R R/W; R W; 3/4 W; 3/4 R; R
Note: The first entry in column ACCESS TYPE is valid between missions. The second entry shows the applicable access type while a mission is in progress. 14 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TIMEKEEPING AND CALENDAR
The real-time clock/alarm and calendar information is accessed by reading/writing the appropriate bytes in the register page, address 200h to 205h. For readings to be valid, all RTC registers must be read sequentially starting at address 0200h. Some of the RTC bits are set to 0. These bits always read 0 regardless of how they are written. The number representation of the real-time clock registers is BCD format (Binary-Coded Decimal).
Real-Time Clock and RTC Alarm Register Bitmap
ADDR 0200h 0201h 0202h 0203h 0204h 0205h b7 0 0 0 0 CENT b6 b5 10 Seconds 10 Minutes
20h. AM/PM
b4
b3
b2 b1 Single Seconds Single Minutes Single Hours Single Date Single Months Single Years
b0
12/24
10h.
0 10 Date 0 0 10m. 10 Years
The real-time clock of the DS1923 can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register (address 202h) is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20 to 23 hours). The CENT bit, bit 7 of the Months Register, can be written by the user. This bit changes its state when the years counter transitions from 99 to 00. The calendar logic is designed to automatically compensate for leap years. For every year value that is either 00 or a multiple of 4 the device will add a 29th of February. This will work correctly up to (but not including) the year 2100.
SAMPLE RATE
The content of the Sample Rate Register (addresses 0206h, 0207h) specifies the time elapse (in seconds if EHSS = 1, or minutes if EHSS = 0) between two temperature/humidity logging events. The sample rate can be any value from 1 to 16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging events is 1 second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and the longest time is 273.05 hours (sample rate = 3FFFh). The EHSS bit is located in the RTC Control Register at address 0212h. It is important that the user sets the EHSS bit accordingly while setting the Sample Rate register. A sample rate of 0000h is not valid and must be avoided under all circumstances. This causes the device to enter into an unrecoverable state.
Sample Rate Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0206h Sample Rate Low 0207h 0 0 Sample Rate High During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be written to 1.
TEMPERATURE CONVERSION
The DS1923 measures temperatures in the range of -20C to +85C. Temperature values are represented as a 8or 16-bit unsigned binary number with a resolution of 0.5C in the 8-bit mode and 0.0625C in the 16-bit mode. The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte TRL are valid. The five lower bits all read zero. TRL is undefined if the device is in 8-bit temperature mode. An outof-range temperature reading is indicated as 00h or 0000h when too cold and FFh or FFE0h when too hot.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Temperature Conversion Result Register Bitmap
ADDR 020Ch 020Dh b7 T2 T10 b6 T1 T9 b5 T0 T8 b4 0 T7 b3 0 T6 b2 0 T5 b1 0 T4 b0 0 T3 TRL TRH
With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is calculated as J(C) = TRH/2 - 41 + TRL/512 J(C) = TRH/2 - 41 (16-bit mode, TLFS = 1, see address 0213h) (8-bit mode, TLFS = 0, see address 0213h)
This equation is valid for converting temperature readings stored in the data log memory as well as for data read from the Latest Temperature Conversion Result Register. To specify the temperature alarm thresholds, the equation above needs to be resolved to TALM = 2 * J (C) + 82 Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5C. The TALM value needs to be converted into hexadecimal format before it can be written to one of the temperature alarm threshold registers (Low Alarm address 0208h; High Alarm address 0209h). Independent of the conversion mode (8- or 16-bit) only the most significant byte of a temperature conversion is used to determine whether an alarm is generated.
Temperature Conversion Examples
Mode 8-bit 8-bit 16-bit 16-bit hex 54h 17h 54h 17h TRH decimal 84 23 84 23 hex 3/4 3/4 00h 60h TRL decimal 3/4 3/4 0 96 J(C) 1.0 -29.5 1.000 -29.3125
Temperature Alarm Threshold Examples
J(C) 25.5 -10.0 TALM hex decimal 85h 133 3Eh 62
HUMIDITY CONVERSION
In addition to temperature, the DS1923 can log humidity data in 8-bit or 16-bit format. Humidity values are represented as 8- or 16-bit unsigned binary numbers with a resolution of 0.64%RH in the 8-bit mode and 0.04 %RH in the 16-bit mode. The DS1923 reads data from its humidity sensor whenever a Forced Conversion command is executed (see Memory/Control Function Commands) or during a mission, if the device is set up to log humidity data. Regardless of its setup, the DS1923 always reads 16 bits from the humidity sensor. The result of the latest humidity reading is found at address 020Eh (low byte) and 020Fh (high byte). The most significant bit read from the humidity sensor will always be found as H11 at address 020Fh. Due to the 12-bit digital output of the humidity sensor, the lower 4 bits in 16-bit format are undefined.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Humidity Conversion Result Register Bitmap
ADDR 020Eh 020Fh b7 H3 H11 b6 H2 H10 b5 H1 H9 b4 H0 H8 b3 X H7 b2 X H6 b1 X H5 b0 X H4 HRL HRH
During a mission, if humidity logging is enabled, the HRH byte (H11 to H4) is always recorded. The HRL byte is only recorded if the DS1923 is set up for 16-bit humidity logging. The logging mode (8-bit or 16-bit) is selected through the HLFS bit at the Mission Control Register, address 0213h. With HRH and HRL representing the decimal equivalent of a humidity reading the actual humidity is calculated according to the algorithms shown in the table below. 16-Bit Mode, HLFS = 1 IVAL = (HRH * 256 + HRL)/16 Round IVAL down to the nearest integer; this eliminates the undefined 4 bits of HRL. ADVAL = IVAL*5.02/4096 HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307 The result is a raw humidity reading that needs to be corrected to achieve the specified accuracy. See the Software Correction Algorithm for Humidity section for further details. To specify the humidity alarm thresholds, the equation needs to be resolved to: ADVAL = HUMIDITY(%RH) * 0.0307 + 0.958 HALM = ADVAL * 256/5.02 Round HALM to the nearest integer. The HALM value needs to be converted into hexadecimal before it can be written to one of the humidity alarm threshold registers (Low Alarm address 020Ah; High Alarm address 020B). Independent of the conversion mode (8-or 16-bit) only the most significant byte of a humidity conversion is used to determine whether an alarm will be generated. The alarm thresholds are applied to the raw humidity readings. Therefore, if software correction is used, the effect of the software correction is to be reversed before calculating a humidity alarm threshold. Example: let the desired alarm threshold be 60%RH. The 60% threshold may correspond to a raw reading of 65%RH (i.e., before correction). To set a 60%RH (after correction) threshold, the HALM value then needs to be calculated for 65%RH. (N/A) ADVAL = HRH*5.02/256 8-Bit Mode, HLFS = 0
Humidity Conversion Examples
Mode 8-bit 8-bit 16-bit 16-bit hex B5h 67h B5h 67h HRH decimal 181 103 181 103 hex 3/4 3/4 C0h 30h HRL decimal 3/4 3/4 12 48 Humidity(%RH) 84.41 34.59 84.89 34.70
Humidity Alarm Threshold Examples
Humidity(%RH) 65 25 HALM hex decimal 97h 151 58h 88
These examples do not include the effects of software correction.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TEMPERATURE SENSOR ALARM
The DS1923 has two Temperature Alarm Threshold registers (address 0208h, 0209h) to store values, which determine whether a critical temperature has been reached. A temperature alarm is generated if the device measures an alarming temperature AND the alarm signaling is enabled. The bits ETLA and ETHA that enable the temperature alarm are located in the Temperature Sensor Control Register. The temperature alarm flags TLF and THF are found in the Alarm Status Register at address 0214h.
Temperature Sensor Control Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0210h 0 0 0 0 0 0 ETHA ETLA During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.
Register Details
Bit Description ETLA: Enable Temperature Low Alarm Bit(s) Definition This bit controls whether, during a mission, the Temperature Low Alarm Flag TLF can be set, if a temperature conversion results in a value equal to or lower than the value in the Temperature Low Alarm Threshold Register. If ETLA is 1, temperature low alarms are enabled. If ETLA is 0, temperature low alarms are not generated. This bit controls whether, during a mission, the Temperature High Alarm Flag THF can be set, if a temperature conversion results in a value equal to or higher than the value in the Temperature High Alarm Threshold Register. If ETHA is 1, temperature high alarms are enabled. If ETHA is 0, temperature high alarms are not generated.
b0
ETHA: Enable Temperature High Alarm
b1
HUMIDITY ALARM
The DS1923 has two Humidity Alarm Threshold registers (address 020Ah, 020Bh) to store values, which determine whether humidity readings can generate an alarm. Such an alarm is generated if the humidity data read from the sensor qualifies for an alarm AND the alarm signaling is enabled. The bits EHLA and EHHA that enable the humidity alarm are located in the Humidity Sensor Control Register. The corresponding alarm flags HLF and HHF are found in the Alarm Status Register at address 0214h.
Humidity Sensor Control Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0211h 1 1 1 1 1 1 EHHA EHLA During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 1 and cannot be written to 0.
Register Details
Bit Description EHLA: Enable Humidity Low Alarm Bit(s) b0 Definition This bit controls whether, during a mission, the Humidity Low Alarm Flag HLF can be set, if a value from the humidity sensor is equal to or lower than the value in the Humidity Low Alarm Threshold Register. If EHLA is 1, humidity low alarms are enabled. If EHLA is 0, humidity low alarms are not generated. This bit controls whether, during a mission, the Humidity High Alarm Flag HHF can be set, if a value from the humidity sensor is equal to or higher than the value in the Humidity High Alarm Threshold Register. If EHHA is 1, humidity high alarms are enabled. If EHHA is 0, humidity high alarms are not generated.
EHHA: Enable Humidity High Alarm
b1
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
REAL-TIME CLOCK CONTROL
To minimize the power consumption of a DS1923, the real-time clock oscillator should be turned off when device is not in use. The oscillator on/off bit is located in the RTC control register. This register also includes the EHSS bit, which determines whether the sample rate is specified in seconds or minutes.
RTC Control Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0212h 0 0 0 0 0 0 EHSS EOSC During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.
Register Details
Bit Description Bit(s) Definition This bit controls the crystal oscillator of the real-time clock. When set to logic 1, the oscillator starts operation. When written to logic 0, the oscillator stops and the device is in a low-power data retention mode. This bit must be 1 for normal operation. A temperature or humidity conversion must not be attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state. This bit controls the speed of the Sample Rate counter. When set to logic 0, the sample rate is specified in minutes. When set to logic 1, the sample rate is specified in seconds.
EOSC: Enable Oscillator
b0
EHSS: Enable High Speed Sample
b1
MISSION CONTROL
The DS1923 is set up for its operation by writing appropriate data to its special function registers, which are located in the two register pages. The settings in the Mission Control Register determine whether temperature and/or humidity is logged, which format (8 or 16 bits) is to be used and whether old data can be overwritten by new data, once the data log memory is full. An additional control bit can be set to tell the DS1923 to wait with logging data until a temperature alarm is encountered.
Mission Control Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0213h 1 1 SUTA RO HLFS TLFS EHL ETL During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and cannot be written to 0.
Register Details
Bit Description ETL: Enable Temperature Logging Bit(s) b0 Definition To set up the device for a temperature-logging mission, this bit must be set to logic 1. To successfully start a mission, ETL or EHL must be 1. If temperature logging is enabled, the recorded temperature values are always stored starting at address 1000h. To set up the DS1923 for a humidity-logging mission, this bit must be set to logic 1. If temperature and humidity logging are enabled, the recorded humidity values will begin at address 2000h (TLFS = HLFS) or 1A00h (TLFS = 0; HLFS = 1) or 2400h (TLFS = 1; HLFS = 0). If only humidity logging is enabled, the recorded values are stored starting at address 1000h. Since humidity data has little scientific value without knowing the temperature, typically both, humidity and temperature logging are enabled, i. e., ETL and EHL are set to 1. This bit specifies the format used to store temperature readings in the data log memory. If this bit is 0, the data will be stored in 8-bit format. If this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit format, the most-significant byte is stored at the lower address. 19 of 52
EHL: Enable Humidity Logging
b1
TLFS: Temperature Logging Format Selection
b2
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory Bit(s) Definition This bit specifies the format used to store humidity readings in the data HLFS: Humidity Logging log memory. If this bit is 0, the data will be stored in 8-bit format. If this b3 Format Selection bit is 1, the 16-bit format is used (higher resolution). With 16-bit format, the most-significant byte is stored at the lower address. This bit controls whether, during a mission, the data log memory is overwritten with new data or whether data logging is stopped once the data log memory is full. Setting this bit to 1 enables the rollover and data RO: Rollover Control b4 logging continues at the beginning, overwriting previously collected data. If this bit is 0, the logging and conversions will stop once the data log memory is full. However, the RTC will continue to run and the MIP bit will remain set until the Stop Mission command is performed. This bit specifies whether a mission begins immediately (includes delayed start) or if a temperature alarm will be required to start the mission. If this bit is 1, the device will perform a temperature conversion at the selected sample rate and begin with data logging only if an SUTA: Start Mission upon alarming temperature (high alarm or low alarm) was found. The first b5 Temperature Alarm logged temperature will be when the alarm occurred. However, the Mission Sample Counter will not increment. The Start Upon Temperature Alarm function is only available if temperature logging is enabled (ETL = 1). Bit Description
ALARM STATUS
The fastest way to determine whether a programmed temperature or humidity threshold was exceeded during a mission is through reading the Alarm Status Register. In a networked environment that contains multiple DS1923 iButtons the devices that encountered an alarm can quickly be identified by means of the Conditional Search command (see ROM Function Commands). The humidity and temperature alarm only occurs if enabled (see Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled.
Alarm Status Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0214h BOR 1 1 1 HHF HLF THF TLF There is only read access to this register. Bits 4 to 6 have no function. They always read 1. All five alarm status bits are cleared simultaneously when the Clear Memory function is invoked. See Memory and Control Functions for details.
Register Details
Bit Description TLF: Temperature Low Alarm Flag Bit(s) b0 Definition If this bit reads 1, there was at least one temperature conversion during a mission revealing a temperature equal to or lower than the value in the Temperature Low Alarm Register. A forced conversion can affect the TLF bit. This bit can also be set with the initial alarm in the SUTA = 1 mode. If this bit reads 1, there was at least one temperature conversion during a mission revealing a temperature equal to or higher than the value in the Temperature High Alarm Register. A forced conversion can affect the THF bit. This bit can also be set with the initial alarm in the SUTA = 1 mode. If this bit reads 1, there was at least one humidity reading during a mission revealing a value equal to or lower than the value in the Humidity Low Alarm Register. A forced conversion can affect the HLF bit. If this bit reads 1, there was at least one humidity reading during a mission revealing a value equal to or higher than the value in the Humidity High Alarm Register. A forced conversion can affect the HHF bit. If this bit reads 1, the device has performed a power-on reset. This indicates that the device has experienced a shock big enough to interrupt the internal battery power supply. The device can still appear functional, but it has lost its factory calibration. Any data found in the data log memory should be disregarded. 20 of 52
THF: Temperature High Alarm Flag HLF: Humidity Low Alarm Flag HHF: Humidity High Alarm Flag BOR: Battery On Reset Alarm
b1
b2 b3
b7
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
GENERAL STATUS
The information in the general status register tells the host computer whether a mission-related command was executed successfully. Individual status bits indicate whether the DS1923 is performing a mission, waiting for a temperature alarm to trigger the logging of data or whether the data from the latest mission has been cleared.
General Status Register Bitmap
ADDR b7 b6 b5 b4 b3 b2 b1 0215h 1 1 0 WFTA MEMCLR 0 MIP There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function. b0 0
Register Details
Bit Description MIP: Mission In Progress Bit(s) b1 Definition If this bit reads 1 the device has been set up for a mission and this mission is still in progress. The MIP bit returns from logic 1 to logic 0 when a mission is ended. See function commands Start Mission and Stop Mission. If this bit reads 1, the Mission Time Stamp, Mission Sample Counter, as well as all the alarm flags of the Alarm Status Register have been cleared in preparation of a new mission. Executing the Clear Memory command clears these memory sections. The MEMCLR bit returns to 0 as soon as a new mission is started by using the Start Mission command. The memory has to be cleared in order for a mission to start. If this bit reads 1, the Mission Start upon Temperature Alarm was selected and the Start Mission command was successfully executed, but the device has not yet experienced the temperature alarm. This bit is cleared after a temperature alarm event, but is not affected by the Clear Memory command. Once set, WFTA remains set if a mission is stopped before a temperature alarm occurs. To clear WFTA manually before starting a new mission, set the high temperature alarm (address 0209h) to -40C and perform a forced conversion.
MEMCLR: Memory Cleared
b3
WFTA: Waiting for Temperature Alarm
b4
MISSION START DELAY
The content of the Mission Start Delay Counter tells how many minutes have to expire from the time a mission was started until the first measurement of the mission will take place (SUTA = 0) or until the device will start testing the temperature for a temperature alarm (SUTA = 1). The Mission Start Delay is stored as an unsigned 24-bit integer number. The maximum delay is 16777215 minutes, equivalent to 11650 days or roughly 31 years. If the start delay is non-zero and the SUTA bit is set to 1, first the delay has to expire before the device starts testing for temperature alarms to begin logging data.
Mission Start Delay Counter
ADDR b7 b6 b5 b4 b3 b2 0216h Delay Low Byte 0217h Delay Center Byte 0218h Delay High Byte During a mission, there is only read access to these registers. b1 b0
For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1923 to store all readings at the selected sample rate, one can use several devices and set the Mission Start Delay for the second device to start recording as soon as the memory of the first device is full, and so on. The RO bit in the Mission Control Register (address 0213h) must be set to 0 to prevent overwriting of collected data once the data log memory is full.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
MISSION TIME STAMP
The Mission Time Stamp indicates the date and time of the first temperature and/or humidity sample of the mission. There is only read access to the Mission Time Stamp Register.
Mission Time Stamp Registers Bitmap
ADDR 0219h 021Ah 021Bh 021Ch 021Dh 021Eh b7 0 0 0 0 CENT b6 12/24 0 0 0 10 Years b5 10 Seconds 10 Minutes
20h. AM/PM
b4 10h.
b3
b2 b1 Single Seconds Single Minutes Single Hours Single Date Single Months Single Years
b0
10 Date 10m.
MISSION PROGRESS INDICATOR
Depending on settings in the Mission Control Register (address 0213h) the DS1923 logs temperature and/or humidity in 8-bit or 16-bit format. The description of the ETL and EHL bit explains where the device stores data in its data log memory. The Mission Sample Counter together with the starting address and the logging format (8 or 16 bits) provides the information to identify valid blocks of data that have been gathered during the current (MIP = 1) or latest mission (MIP = 0). See section Data log Memory Usage for an illustration. Note that when SUTA = 1, the Mission Sample Counter does not increment when the first sample is logged.
Mission Sample Counter Register Map
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0220h Low Byte 0221h Center Byte 0222h High Byte There is only read access to this register. Note that when both the internal temperature and humidity logging are enabled, the two log readings are counted as one event in the Mission Sample Counter and Device Sample Counter. The number read from the Mission Sample Counter indicates how often the DS1923 woke up during a mission to measure temperature and/or humidity. The number format is 24-bit unsigned integer. The Mission Sample Counter is reset through the Clear Memory command.
OTHER INDICATORS
The Device Sample Counter is similar to the Mission Sample Counter. During a mission this counter increments whenever the DS1923 wakes up to measure and log data and when the device is testing for a temperature alarm in SUTA mode. Between missions the counter increments whenever the Forced Conversion command is executed. This way the Device Sample Counter functions like a gas gauge for the battery that powers the iButton.
Device Sample Counter Register Map
ADDR b7 b6 b5 0223h 0224h 0225h There is only read access to this register. b4 b3 Low Byte Center Byte High Byte b2 b1 b0
The Device Sample Counter is reset to zero when the iButton is assembled. The counter increments a couple of times during final test. The number format is 24-bit unsigned integer. The maximum number that can be represented in this format is 16777215. The Device Configuration Byte is used to allow the master to distinguish between the DS2422 chip, and the DS1923, DS1922L, and DS1922T iButtons. The table below shows the codes assigned to the various devices. 22 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Device Configuration Byte
ADDR b7 b6 b5 b4 b3 0226h 0 0 0 0 0 0226h 0 0 1 0 0 0226h 0 1 0 0 0 0226h 0 1 1 0 0 There is only read access to this register. b2 0 0 0 0 b1 0 0 0 0 b0 0 0 0 0 DS2422 DS1923 DS1922L DS1922T
SECURITY BY PASSWORD
The DS1923 is designed to use two passwords that control read access and full access. Reading from or writing to the scratchpad as well as the forced conversion command does not require a password. The password needs to be transmitted right after the command code of the memory or control function. If password checking is enabled the password transmitted is compared to the passwords stored in the device. The data pattern stored in the Password Control register determines whether password checking is enabled.
Password Control Register
ADDR b7 b6 b5 b4 b3 0227h EPW During a mission, there is only read access to this register. b2 b1 b0
To enable password checking, the EPW bits need to form a binary pattern of 10101010 (AAh). The default pattern of EPW is different from AAh. If the EPW pattern is different from AAh, any pattern will be accepted, as long as it has a length of exactly 64 bits. Once enabled, changing the passwords and disabling password checking requires the knowledge of the current full-access password. Before enabling password checking, passwords for read-only access as well as for full access (read/write/control) need to be written to the password registers. Setting up a password or enabling/disabling the password checking is done in the same way as writing data to a memory location, only the address is different. Since they are located in the same memory page, both passwords can be redefined at the same time.
Read Access Password Register
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0228h RP7 RP6 RP5 RP4 RP3 RP2 RP1 RP0 0229h RP15 RP14 RP13 RP12 RP11 RP10 RP9 RP8 3/4 3/4 3/4 022Eh RP55 RP54 RP53 RP52 RP51 RP50 RP49 RP48 022Fh RP63 RP62 RP61 RP60 RP59 RP58 RP57 RP56 There is only write access to this register. Attempting to read the password will report all zeros. The password cannot be changed while a mission is in progress. The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1... RP62, RP63. This password only applies to the function "Read Memory with CRC". The DS1923 delivers the requested data only if the password transmitted by the master was correct or if password checking is not enabled.
Full-Access Password Register
ADDR b7 b6 b5 b4 b3 b2 b1 b0 0230h FP7 FP6 FP5 FP4 FP3 FP2 FP1 FP0 0231h FP15 FP14 FP13 FP12 FP11 FP10 FP9 FP8 3/4 3/4 3/4 0236h FP55 FP54 FP53 FP52 FP51 FP50 FP49 FP48 0237h FP63 FP62 FP61 FP60 FP59 FP58 FP57 FP56 There is only write access to this register. Attempting to read the password will report all zeros. The password cannot be changed while a mission is in progress.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1... FP62, FP63. It affects the functions "Read Memory with CRC", "Copy Scratchpad", "Clear Memory", "Start Mission", and "Stop Mission". The DS1923 executes the command only if the password transmitted by the master was correct or if password checking is not enabled Due to the special behavior of the write access logic, the Password Control Register and both passwords must be written at the same time. When setting up new passwords, always verify (read back) the scratchpad before sending the copy scratchpad command. After a new password is successfully copied from the scratchpad to its memory location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the passwords will remain in the scratchpad for public read access.
DATA LOG MEMORY USAGE
Once setup for a mission, the DS1923 logs the temperature measurements and/or humidity at equidistant time points entry after entry in its data log memory. The data log memory is able to store 8192 entries in 8-bit format or 4096 entries in 16-bit format (Figure 7A). If temperature as well as humidity is logged, both in the same format, the memory is split into two equal sections that can store 4096 8-bit entries or 2048 16-bit entries (Figure 7B). If the device is set up to log data in different formats, e. g., temperature in 8-bit and humidity in 16-bit format, the memory is split into blocks of different size, accommodating 2560 entries for either data source (Figure 7C). In this case, the upper 256 bytes are not used. In 16-bit format, the higher 8 bits of an entry are stored at the lower address. Knowing the starting time point (Mission Time Stamp) and the interval between temperature measurements one can reconstruct the time and date of each measurement. There are two alternatives to the way the DS1923 behaves after the data log memory is filled with data. The user can program the device to either stop any further recording (disable "rollover") or overwrite the previously recorded data (enable "rollover"), one entry at a time, starting again at the beginning of the respective memory section. The contents of the Mission Sample Counter in conjunction with the sample rate and the Mission Time Stamp then allows reconstructing the time points of all values stored in the data log memory. This gives the exact history over time for the most recent measurements taken. Earlier measurements cannot be reconstructed.
Figure 7A. ONE CHANNEL LOGGING
ETL = 1; EHL = 0 or ETL = 0; EHL = 1 TLFS = HLFS = 0 1000h ETL = 1; EHL = 0 or ETL = 0; EHL = 1 TLFS = HLFS = 1 1000h
8192 8-bit entries Temperature or Humidity data
4096 16-bit entries Temperature or Humidity data
With 16-bit format, the most-significant byte is stored at the lower address.
2FFFh
2FFFh
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 7B. TWO CHANNEL LOGGING, EQUAL RESOLUTION
ETL = EHL = 1 TLFS = HLFS = 0 1000h Temperature 4096 8-bit entries 1FFFh 2000h Humidity Data 4096 8-bit entries 2FFFh Humidity Data 2048 16-bit entries 2FFFh Temperature 2048 16-bit entries 1FFFh 2000h ETL = EHL = 1 TLFS = HLFS = 1 1000h
With 16-bit format, the most-significant byte is stored at the lower address.
Figure 7C. TWO CHANNEL LOGGING, DIFFERENT RESOLUTION
ETL = EHL = 1 TLFS = 0; HLFS = 1 Temperature 2560 8-bit entries 1000h 19FFh 1A00h Temperature 2560 16-bit entries 23FFh Humidity Data 2560 8-bit entries (not used) 2400h 2DFFh
2E00h 2FFFh
ETL = EHL = 1 TLFS = 1; HLFS = 0 1000h
Humidity Data 2560 16-bit entries 2DFFh (not used)
2E00h 2FFFh
With 16-bit format, the most-significant byte is stored at the lower address.
MISSIONING
The typical task of the DS1923 iButton is recording temperature and/or humidity. Before the device can perform this function, it needs to be set up properly. This procedure is called missioning. First of all, DS1923 needs to have its real-time clock set to valid time and date. This reference time may be the local time, or, when used inside of a mobile unit, UTC (also called GMT, Greenwich Mean Time) or any other time standard that was agreed upon. The real-time clock oscillator must be running (EOSC = 1). The memory assigned to store the Mission Time Stamp, Mission Sample Counter, and Alarm Flags must be cleared using the Memory Clear command. To enable the device for a mission, at least one of the enable logging bits (ETL, EHL) must be set to 1. These are general settings that have to be made in any case, regardless of the type of object to be monitored and the duration of the mission. If alarm signaling is desired, the temperature alarm and/or humidity alarm low and high thresholds must be defined. How to convert a temperature value into the binary code to be written to the threshold registers is described under "Temperature Conversion" earlier in this document. Determining the thresholds for the humidity alarm is described in section "Humidity Conversion". In addition, the temperature and/or humidity alarm must be enabled for the low25 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory and/or high-threshold. This will make the device respond to a Conditional Search command (see ROM Function Commands), provided that an alarming condition has been encountered. The setting of the RO bit (rollover enable) and sample rate depends on the duration of the mission and the monitoring requirements. If the most recently logged data is important, the rollover should be enabled (RO = 1). Otherwise one should estimate the duration of the mission in minutes and divide the number by 8192 (single channel 8-bit format) or 4096 (single channel 16-bit format, two channels 8-bit format) or 2048 (two channels 16-bit format) or 2560 (two channels, one 8-bit and one 16-bit format) to calculate the value of the sample rate (number of minutes between conversions). If the estimated duration of a mission is 10 days (= 14400 minutes), for example, then the 8192-byte capacity of the data log memory would be sufficient to store a new 8-bit value every 1.8 minutes (110 seconds). If the data log memory of the DS1923 is not large enough to store all readings, one can use several devices and set the Mission Start Delay to values that make the second device start logging as soon as the memory of the first device is full, and so on. The RO-bit needs to be set to 0 to disable rollover that would otherwise overwrite the logged data. After the RO bit and the Mission Start Delay are set, the sample rate needs to be written to the Sample Rate Register. The sample rate may be any value from 1 to 16383, coded as an unsigned 14-bit binary number. A sample rate of all zeros is not valid and must be avoided under all circumstances. This causes the device to enter into an unrecoverable state. The fastest sample rate is one sample per second (EHSS = 1, Sample Rate = 0001h) and the slowest is one sample every 273.05 hours (EHSS = 0, Sample Rate = 3FFFh). To get one sample every 6 minutes, for example, the sample rate value needs to be set to 6 (EHSS = 0) or 360 decimal (equivalent to 0168h at EHSS = 1). If there is a risk of unauthorized access to the DS1923 or manipulation of data, one should define passwords for read access and full access. Before the passwords become effective, their use needs to be enabled. See Security by Password for more details. The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command, the DS1923 sets the MIP flag and clear the MEMCLR flag. With the immediate/delayed start mode (SUTA = 0), after as many minutes as specified by the Mission Start Delay are over, the device wakes up, copies the current date and time to the mission time stamp register, and logs the first entry of the mission. This increments both the Mission Sample Counter and Device Sample Counter. All subsequent log entries are made as specified by the value in the Sample Rate Register and the EHSS bit. If the Start Upon Temperature Alarm mode is chosen (SUTA = 1) and temperature logging is enabled (ETL = 1) the DS1923 first waist until the start delay is over. Then the device wakes up in intervals as specified by the sample rate and EHSS bit and measure the temperature. This increments the Device Sample Counter only. The first sample of the mission is logged when the temperature alarm occurred. However, the Mission Sample Counter will not increment. One sample period later the Mission Time Stamp is set. From then on, both the Mission Sample Counter and Device Sample Counter increment at the same time. All subsequent log entries will be made as specified by the value in the Sample Rate Register and the EHSS bit. The general-purpose memory operates independently of the other memory sections and is not write-protected during a mission. All memory of the DS1923 can be read at any time, e. g., to watch the progress of a mission. Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.
ADDRESS REGISTERS AND TRANSFER STATUS
Because of the serial data transfer, the DS1923 employs three address registers, called TA1, TA2, and E/S (Figure 8). Registers TA1 and TA2 must be loaded with the target address to which the data will be written or from which data will be sent to the master upon a Read command. Register E/S acts like a byte counter and transfer status register. It is used to verify data integrity with Write commands. Therefore, the master only has read access to this register. The lower 5 bits of the E/S Register indicate the address of the last byte that has been written to the scratchpad. This address is called Ending Offset. The DS1923 requires that the Ending Offset is always 1Fh for a Copy Scratchpad to function. Bit 5 of the E/S Register, called PF or "partial byte flag," is set if the number of data bits sent by the master is not an integer multiple of 8. Bit 6 is always a 0. Note that the lowest 5 bits of the target address also determine the address within the scratchpad, where intermediate storage of data begins. This address is called byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad stores incoming data beginning at the byte offset 1Ch and is full after only 4 bytes. The corresponding ending offset 26 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point to the beginning of a page, i.e., the byte offset is 0. Thus the full 32-byte capacity of the scratchpad is available, resulting also in the ending offset of 1Fh. The ending offset together with the Partial and Overflow Flag is mainly a means to support the master checking the data integrity after a Write command. The highest valued bit of the E/S Register, called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been received and executed. Writing data to the scratchpad clears this flag.
Figure 8. ADDRESS REGISTERS
Bit # Target Address (TA1) 7 T7 6 T6 5 T5 4 T4 3 T3 2 T2 1 T1 0 T0
Target Address (TA2) Ending Address with Data Status (E/S) (Read Only)
T15
T14
T13
T12
T11
T10
T9
T8
AA
0
PF
E4
E3
E2
E1
E0
WRITING WITH VERIFICATION
To write data to the DS1923, the scratchpad has to be used as intermediate storage. First the master issues the Write Scratchpad command to specify the desired target address, followed by the data to be written to the scratchpad. In the next step, the master sends the Read Scratchpad command to read the scratchpad and to verify data integrity. As preamble to the scratchpad data, the DS1923 sends the requested target address TA1 and TA2 and the contents of the E/S Register. If the PF flag is set, data did not arrive correctly in the scratchpad. The master does not need to continue reading; it can start a new trial to write data to the scratchpad. Similarly, a set AA flag indicates that the Write command was not recognized by the device. If everything went correctly, both flags are cleared and the ending offset indicates the address of the last byte written to the scratchpad. Now the master can continue verifying every data bit. After the master has verified the data, it has to send the Copy Scratchpad command. This command must be followed exactly by the data of the three address registers TA1, TA2, and E/S as the master has read them verifying the scratchpad. As soon as the DS1923 has received these bytes, it copies the data to the requested location beginning at the target address.
MEMORY- AND CONTROL-FUNCTION COMMANDS
The "Memory/Control Function Flow Chart" (Figure 9) describes the protocols necessary for accessing the memory and the special function registers of the DS1923. An example on how to use these and other functions to set up the DS1923 for a mission is included at the end of this document, preceding the Electrical Characteristics section. The communication between master and DS1923 takes place either at regular speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive Mode the DS1923 assumes regular speed. Internal memory access during a mission has priority over external access through the 1-Wire interface. This affects several of the commands described below. See Memory Access Conflicts for details and remedies.
Write Scratchpad Command [0Fh]
After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by the data to be written to the scratchpad. The data will be written to the scratchpad starting at the byte offset (T4:T0). The master has to send as many bytes as are needed to reach the Ending Offset of 1Fh. If a data byte is incomplete, its content is ignored and the partial byte flag PF is set. When executing the Write Scratchpad command the CRC generator inside the DS1923 (see Figure 15) calculates a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by the master. 27 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory This CRC is generated using the CRC16 polynomial by first clearing the CRC generator and then shifting in the command code (0Fh) of the Write Scratchpad command, the Target Addresses TA1 and TA2 as supplied by the master and all the data bytes. If the ending offset is 11111b, the master may send 16 read time slots and will receive the inverted CRC16 generated by the DS1923. Note that both register pages are write-protected during a mission. Although the Write Scratchpad command will work normally at any time, the subsequent copy scratchpad to a register page will fail during a mission.
Read Scratchpad Command [AAh]
This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad command, the master begins reading. The first 2 bytes will be the target address. The next byte will be the ending offset/data status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0), as shown in Figure 8. The master may continue reading data until the end of the scratchpad after which it will receive an inverted CRC16 of the command code, Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target address. After the CRC is read, the bus master will read logical 1s from the DS1923 until a reset pulse is issued.
Copy Scratchpad with Password [99h]
This command is used to copy data from the scratchpad to the writable memory sections. After issuing the Copy Scratchpad command, the master must provide a 3-byte authorization pattern, which can be obtained by reading the scratchpad for verification. This pattern must exactly match the data contained in the three address registers (TA1, TA2, E/S, in that order). Next the master must transmit the 64-bit full-access password. If passwords are enabled and the transmitted password is different from the stored full-access password, the Copy Scratchpad with Password command will fail. Then the device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device tests the 3-byte authorization code. If the authorization code pattern matches, the AA (Authorization Accepted) flag is set and the copy begins. A pattern of alternating 1s and 0s are transmitted after the data has been copied until the master issues a reset pulse. While the copy is in progress any attempt to reset the part is ignored. Copy typically takes 2s per byte. The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset through the ending offset will be copied, starting at the target address. The AA flag remains at logic 1 until it is cleared by the next Write Scratchpad command. With suitable password, the copy scratchpad always functions for the 16 pages of data memory and the 2 pages of calibration memory. While a mission is in progress, write attempts to the register pages will not be successful. The AA bit (Authorization Accepted) remaining at 0 will indicate this.
Read Memory with Password and CRC [69h]
The Read Memory with CRC command is the general function to read from the device. This command generates and transmits a 16-bit CRC following the last data byte of a memory page. After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte address that indicates a starting byte location. Next the master must transmit one of the 64-bit passwords. If passwords are enabled and the transmitted password does not match one of the stored passwords, the Read Memory with Password and CRC command fails. The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the master reads data from the DS1923 beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus master sends 16 additional read data time slots and receive the inverted 16-bit CRC. With subsequent read-data time slots the master will receive data starting at the beginning of the next memory page followed again by the CRC for that page. This sequence continues until the bus master resets the device. When trying to read the passwords or memory areas that are marked as "reserved", the DS1923 transmits 00h or FFh bytes, respectively. The CRC at the end of a 32-byte memory page is based on the data as it was transmitted. With the initial pass through the Read Memory with CRC flow, the 16-bit CRC value is the result of shifting the command byte into the cleared CRC generator followed by the 2 address bytes and the contents of the data memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of the last page is read, the bus master receives logical 1s from the DS1923 until a reset pulse is issued. The Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-1. MEMORY/CONTROL FUNCTION FLOW CHART
Master TX Memory or Control Fkt. Command 0FH Write Scratchpad Y Master TX TA1 (T7:T0) Master TX TA2 (T15:T8) DS1923 sets Scratchpad Offset = (T4:T0) and Clears (PF, AA) Master TX Data Byte to Scratchpad Offset DS1923 sets (E4:E0) = Scratchpad Offset Y DS1923 Increments Scratchpad Offset N N From ROM Functions Flow Chart (Figure 11) AAH Read Scratchpad Y Master RX TA1 (T7:T0) Master RX TA2 (T15:T8) Master RX Ending Offset with Data Status (E/S) DS1923 sets Scratchpad Offset = (T4:T0) Master RX Data Byte from Scratchpad Offset Y N
Master TX Reset? DS1923 Increments Scratchpad Offset N N Scratchpad Offset = 11111b? Y Y Master TX Reset? N
Master TX Reset? N Scratchpad Offset = 11111b? Y
Partial Byte Written? N
Y
PF = 1
Master RX CRC16 of Command, Address Data, E/S Byte, and Data Starting at the Target Address
Master RX CRC16 of Command, Address Data
Y
Master TX Reset? N Master RX "1"s
Y
Master TX Reset? N Master RX "1"s
To ROM Functions Flow Chart (Figure 11)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-2. MEMORY/CONTROL FUNCTION FLOW CHART
99H Copy Scrpd. [w/PW] Y Master TX TA1 (T7:T0), TA2 (T15:T8) Master TX E/S Byte Master TX 64-Bits [Password]
N
Authorization Code
Password Accepted? Y Authorization Code Match? Y AA = 1
N
N
DS1923 Copies Scratchpad Data to Memory
Master RX "1"s N Copying Finished Y DS1923 TX "0" Y
Master RX "1"s N
Master TX Reset? Y
Master TX Reset? N DS1923 TX "1"
N
Master TX Reset? Y
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-3. MEMORY/CONTROL FUNCTION FLOW CHART
69H Read Mem. [w/PW]&CRC Y Master TX TA1 (T7:T0), TA2 (T15:T8) Master TX 64-Bits [Password] N
N
Decision made by DS1923
Password Accepted? Y Decision made by Master DS1923 sets Memory Address = (T15:T0) Master RX Data Byte from Memory Address
Y
Master TX Reset? N End of Page? Y Master RX CRC16 of Command, Address, Data st (1 Pass); CRC16 of Data (Subsequent Passes) N
DS1923 Increments Address Counter
Master TX Reset
N
CRC OK? Y End of Memory? Y Master TX Reset? Y Master RX "1"s N N
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-4. MEMORY/CONTROL FUNCTION FLOW CHART
96H Clear Mem. [w/PW] Y Master TX 64-Bits [Password] Master TX FFh dummy byte
N
55H Forced Conversion? Y Master TX FFh dummy byte
N
Mission in Progress? N N DS1923 Performs a Temp. Conversion Y DS1923 copies Result to Address 020C/Dh DS1923 Performs a Humidity Conversion DS1923 copies Result to Address 020E/Fh
Y
Password Accepted? Y Mission in Progress? N DS1923 clears Mission Time Stamp, Mission Samples Counter, Alarm Flags
N DS1923 sets MEMCLR = 1
Master TX Reset? Y
N
Master TX Reset? Y
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-5. MEMORY/CONTROL FUNCTION FLOW CHART
CCH Start Mission [w/PW] Y Master TX 64-Bits [Password] Master TX FFh dummy byte N Password Accepted? Y Y Mission in Progress? N N MEMCLR = 1? Y DS1923 sets MIP = 1 MEMCLR = 0 DS1923 Initiates Mission Start Delay Process
N Mission Start Delay Process Y
33H Stop Mission [w/PW] Y Master TX 64-Bits [Password] Master TX FFh dummy byte
N
Start Delay Counter = 0? N
DS1923 Waits for 1 Minute DS1923 decrements Start Delay Counter Password Accepted? Y SUTA = 1? Y DS1923 Sets WFTA=1 DS1923 Waits One Sample Period Y MIP = 0? N DS1923 Performs 8-bit Temp. Conversion Temp. Alarm? Y DS1923 sets WFTA=0 and logs first sample DS1923 Waits One Sample Period DS1923 copies RTC Data to Mission Time Stamp Register N Master TX Reset? Y N Mission in Progress? Y DS1923 sets MIP = 0 WFTA = 0
N
N
N
The Mission Sample Counter will not increment.
N
Master TX Reset? Y
DS1923 Starts Logging Taking 1st Sample End Of Process
If SUTA = 1, this is the 2nd sample.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Clear Memory with Password [96h]
The Clear Memory with Password command is used to prepare the device for another mission. This command is only executed if no mission is in progress. After the command code the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is in progress, the Clear Memory with Password command will fail. The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the device will clear the Mission Time Stamp, Mission Sample Counter, and all alarm flags of the Alarm Status Register. After these cells are cleared, the MEMCLR bit of the General Status Register reads 1 to indicate the successful execution of the Clear Memory with Password command. Clearing of the data log memory is not necessary because the Mission Sample Counter indicates how many entries in the data log memory are valid.
Forced Conversion [55h]
The Forced Conversion command can be used to measure the temperature and humidity without starting a mission. After the command code the master has to send one FFh byte to get the conversion started. The conversion result is found as 16-bit value in the Latest Temperature Conversion Result and Latest Humidity Conversion Result registers. This command is only executed if no mission is in progress (MIP = 0). It cannot be interrupted and takes maximum 666ms to complete. During this time memory access through the 1-Wire interface is blocked. The device behaves the same way as during a mission when the sampling interferes with a memory/control function command. See Memory Access Conflicts for details. A forced conversion must not be attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state.
Start Mission with Password [CCh]
The DS1923 uses a control function command to start a mission. A new mission can only be started if the previous mission has been ended and the memory has been cleared. After the command code, the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is in progress, the Start Mission with Password command will fail. The device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device starts a mission. If SUTA = 0, the sampling begins as soon as the mission start delay is over. If SUTA = 1, the first sample is written to the data log memory at the time the temperature alarm occurred. However, the Mission Sample Counter does not increment. One sample period later, the Mission Time Stamp will be set and the regular sampling and logging begins. While the device is waiting for a temperature alarm to occur, the WFTA flag in the general status register will read 1. During a mission there is only read access to the Register Pages.
Stop Mission with Password [33h]
The DS1923 uses a control function command to stop a mission. Only a mission that is in progress can be stopped. After the command code, the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is not in progress, the Stop Mission with Password command will fail. The device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device clears the MIP bit in the General Status Register and restore write access to the Register Pages. The WFTA bit is not cleared. See the description of the General Status Register for a method to clear the WFTA bit.
MEMORY ACCESS CONFLICTS
While a mission is in progress or while the device is waiting for a temperature alarm to start a mission, periodically a temperature and/or humidity sample is taken and logged. This "internal activity" has priority over 1-Wire communication. As a consequence, device-specific commands (excluding ROM function commands and 1-Wire reset) will not perform properly when internal and "external" activities interfere with each other. Not affected are the commands Start Mission, Forced Conversion, and Clear Memory because they are not applicable while a mission is in progress or while the device is waiting for a temperature alarm. The table below explains how the remaining five commands are affected by internal activity, how to detect this interference and how to work around it.
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Command Write Scratchpad
Read Scratchpad
Copy Scratchpad
Read Memory with CRC
Stop Mission
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory Indication of Interference Remedy Wait 0.5 seconds, 1-Wire reset, address the device, repeat Write Scratchpad with the same data, and The CRC16 at the end of the check the validity of the CRC16 at the end of the command flow reads FFFFh. command flow. Alternatively, use Read Scratchpad to verify data integrity. The data read changes to FFh Wait 0.5 seconds, 1-Wire reset, address the device, bytes or all bytes received are repeat Read Scratchpad, and check the validity of the FFh, including the CRC at the CRC16 at the end of the command flow. end of the command flow. Wait 0.5 seconds, 1-Wire reset, address the device, The device behaves as if authorization code or password issue Read Scratchpad and check the AA-bit of the E/S byte. If the AA-bit is set, Copy Scratchpad was was not valid or as if the copy successful. function would not end. The data read changes to all FFh bytes or all bytes received Wait 0.5 seconds, 1-Wire reset, address the device, are FFh, including the CRC at repeat Read Memory with CRC, and check the validity the end of the command flow, of the CRC16 at the end of the memory page. despite a valid password. Wait 0.5 seconds, 1-Wire reset, address the device, The general Status register at and repeat Stop Mission. Perform a 1-Wire reset, address 215h reads FFh or the address the device, read the general Status register at MIP bit is 1 while bits 0, 2, and address 215h and check the MIP-bit. If the MIP-bit is 0, 5 are 0. Stop Mission was successful.
The interference is more likely to be seen with a high sample rate (1 sample every second) and with high-resolution logging, which can last up to 666ms when both temperature and humidity are recorded. With lower sample rates interference may hardly be visible at all. In any case, when writing driver software, it is important to know about the possibility of interference and to take measures to work around it.
1-WIRE BUS SYSTEM
The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1923 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The 1-Wire protocol defines bus transactions in terms of the bus state during specific time slots that are initiated on the falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of the Book of DS19xx iButton Standards.
HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open drain or tri-state outputs. The 1-Wire port of the DS1923 is open-drain with an internal circuit equivalent to that shown in Figure 10. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus has a maximum data rate of 16.3kbps. The speed can be boosted to 142kbps by activating the Overdrive mode. The DS1923 is not guaranteed to be fully compliant to the iButton Standard. Its maximum data rate in standard speed mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the network size and load conditions. The DS1923 requires a pullup resistor of maximum 2.2kW at any speed. The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16s (Overdrive speed) or more than 120s (standard speed), one or more devices on the bus may be reset. Note that the DS19233 does not quite meet the full 16s maximum low time of the normal 1-Wire bus Overdrive timing. With the DS1923 the bus must be left low for no longer than 12s at Overdrive to ensure that no DS1923 on the 1-Wire bus performs a reset. The DS1923 communicates properly when used in conjunction with a DS2480B or DS2490 1-Wire driver and adapters that are based on these driver chips.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 10. HARDWARE CONFIGURATION
BUS MASTER VPUP RPUP RX DATA 5 A Typ. 100 W MOSFET RX TX DS1923 1-Wire PORT
TX Open Drain Port Pin
RX = RECEIVE TX = TRANSMIT
TRANSACTION SEQUENCE
The protocol for accessing the DS1923 through the 1-Wire port is as follows: Initialization ROM Function Command Memory/Control Function Command Transaction/Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS1923 is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section.
1-Wire ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the eight ROM function commands that the DS1923 supports. All ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure 11).
Read ROM [33h]
This command allows the bus master to read the DS1923's 8-bit family code, unique 48-bit serial number, and 8-bit CRC. This command can only be used if there is a single slave on the bus. If more than one slave is present on the bus, a data collision occurs when all slaves try to transmit at the same time (open-drain produces a wired-AND result). The resultant family code and 48-bit serial number results in a mismatch of the CRC.
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a specific DS1923 on a multidrop bus. Only the DS1923 that exactly matches the 64-bit ROM sequence responds to the following memory function command. All other slaves will wait for a reset pulse. This command can be used with a single or multiple devices on the bus.
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-Wire bus or their registration numbers. By taking advantage of the wired-AND property of the bus, the master can use a process of elimination to identify the registration numbers of all slave devices. For each bit of the registration number, starting with the least significant bit, the bus master issues a triplet of time slots. On the first slot, each slave device participating in the search outputs the true value of its registration number bit. On the second slot, each slave device participating in the search outputs the complemented value of its registration number bit. On the third slot, the master writes the true value of the bit to be selected. All slave devices that do not match the bit written by the master stop participating in the search. If both of the read bits are zero, the master knows that slave 36 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory devices exist with both states of the bit. By choosing which state to write, the bus master branches in the romcode tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify the registration numbers of the remaining devices. Refer to App Note 187: 1-Wire Search Algorithm for a detailed discussion, including an example.
Conditional Search [ECh]
The Conditional Search ROM command operates similarly to the Search ROM command except that only those devices, which fulfill certain conditions, participate in the search. This function provides an efficient means for the bus master to identify devices on a multidrop system that have to signal an important event. After each pass of the conditional search that successfully determined the 64-bit ROM code for a specific device on the multidrop bus, that particular device can be individually accessed as if a Match ROM had been issued, since all other devices have dropped out of the search process and will be waiting for a reset pulse. The DS1923 responds to the conditional search if one of the five alarm flags of the Alarm Status Register (address 0214h) reads 1. The humidity and temperature alarm only occurs if enabled (see Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled. The first alarm that occurs makes the device respond to the Conditional Search command.
Skip ROM [CCh]
This command can save time in a single-drop bus system by allowing the bus master to access the memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a Read command is issued following the Skip ROM command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wired-AND result).
Resume Command [A5h]
The DS1923 needs to be accessed several times before a mission starts. In a multidrop environment this means that the 64-bit ROM code after a Match ROM command has to be repeated for every access. To maximize the data throughput in a multidrop environment, the Resume function was implemented. This function checks the status of the RC bit and, if it is set, directly transfers control to the Memory/Control functions, similar to a Skip ROM command. The only way to set the RC bit is through successfully executing the Match ROM, Search ROM or Overdrive Match ROM command. Once the RC bit is set, the device can repeatedly be accessed through the Resume Command function. Accessing another device on the bus will clear the RC bit, preventing two or more devices from simultaneously responding to the Resume Command function.
Overdrive Skip ROM [3Ch]
On a single-drop bus this command can save time by allowing the bus master to access the memory/control functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets the DS1923 in the Overdrive mode (OD = 1). All communication following this command has to occur at Overdrive speed until a reset pulse of minimum 690s duration resets all devices on the bus to standard speed (OD = 0). When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive mode. To subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed has to be issued followed by a Match ROM or Search ROM command sequence. This speeds up the time for the search process. If more than one slave supporting Overdrive is present on the bus and the Overdrive Skip ROM command is followed by a Read command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns will produce a wired-AND result).
Overdrive Match ROM [69h]
The Overdrive Match ROM command followed by a 64-bit ROM sequence transmitted at Overdrive Speed allows the bus master to address a specific DS1923 on a multidrop bus and to simultaneously set it in Overdrive mode. Only the DS1923 that exactly matches the 64-bit ROM sequence will respond to the subsequent memory/control function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive Match command remains in Overdrive mode. All overdrive-capable slaves return to standard speed at the next Reset Pulse of minimum 690s duration. The Overdrive Match ROM command can be used with a single or multiple devices on the bus.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 11-1. ROM FUNCTIONS FLOW CHART
From Memory Functions Flow Chart (Figure 9) Bus Master TX Reset Pulse OD Reset Pulse? Y Bus Master TX ROM Function Command 33h Read ROM Command? Y RC = 0 N DS1923 TX Presence Pulse 55h Match ROM Command? Y RC = 0 N F0h Search ROM Command? Y RC = 0 N Condition Met? Y DS1923 TX Family Code (1 Byte) Master TX Bit 0 N Y DS1923 TX Serial Number (6 Bytes) Master TX Bit 1 N Y DS1923 TX CRC Byte Master TX Bit 63 N N DS1923 TX Bit 0 DS1923 TX Bit 0 Master TX Bit 0 Bit 0 Match? Y DS1923 TX Bit 1 DS1923 TX Bit 1 Master TX Bit 1 Bit 1 Match? Y DS1923 TX Bit 63 DS1923 TX Bit 63 Master TX Bit 63 N Y RC = 1 RC = 1 N Bit 63 Match? Y RC = 1 N N N DS1923 TX Bit 0 DS1923 TX Bit 0 Master TX Bit 0 Bit 0 Match? Y DS1923 TX Bit 1 DS1923 TX Bit 1 Master TX Bit 1 Bit 1 Match? Y DS1923 TX Bit 63 DS1923 TX Bit 63 Master TX Bit 63 Bit 63 Match? Y To Figure 11 nd 2 Part From Figure 11 nd 2 Part N To Figure 11 nd 2 Part N N From Figure 11, 2
nd
Part
OD = 0
ECh Cond. Search Command? Y RC = 0
Bit 0 Match?
Bit 1 Match?
Bit 63 Match?
To Memory Functions Flow Chart (Figure 9)
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 11-2. ROM FUNCTIONS FLOW CHART
To Figure 11, 1 Part
st
From Figure 11 st 1 Part CCh Skip ROM Command? Y N A5h Resume Command? Y N 3Ch Overdrive Skip ROM? Y N 69h N Overdrive Match ROM? Y
RC = 0 N
RC = 0 ; OD = 1
RC = 0 ; OD = 1
RC = 1 ? Y
Master TX Bit 0 Y N Y Master TX Bit 1 Y N Y Master TX Bit 63
Master TX Reset ? N
Bit 0 Match?
Master TX Reset ? N
Bit 1 Match?
Bit 63 Match? From Figure 11 st 1 Part To Figure 11 st 1 Part Y RC = 1
N
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
1-WIRE SIGNALING
The DS1923 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One and Read-Data. Except for the presence pulse the bus master initiates all these signals. The DS1923 can communicate at two different speeds, standard speed and Overdrive Speed. If not explicitly set into the Overdrive mode, the DS1923 communicates at standard speed. While in Overdrive Mode the fast timing applies to all waveforms. To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP below the threshold VTL. To get from active to idle, the voltage needs to rise from VILMAX past the threshold VTH. The time it takes for the voltage to make this rise is seen in Figure 12 as 'e' and its duration depends on the pullup resistor (RPUP) used and the capacitance of the 1-Wire network attached. The voltage VILMAX is relevant for the DS1923 when determining a logical level, not triggering any events. The initialization sequence required to begin any communication with the DS1923 is shown in Figure 12. A Reset Pulse followed by a Presence Pulse indicates the DS1923 is ready to receive data, given the correct ROM and memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line for tRSTL + tF to compensate for the edge. A tRSTL duration of 690s or longer will exit the Overdrive Mode returning the device to standard speed. If the DS1923 is in Overdrive Mode and tRSTL is no longer than 80s the devices remain in Overdrive Mode.
Figure 12. INITIALIZATION PROCEDURE "RESET AND PRESENCE PULSES"
MASTER TX "RESET PULSE" MASTER RX "PRESENCE PULSE" VPUP VIHMASTER VTH VTL VILMAX 0V e tMSP
tF
tRSTL
tPDH MASTER
tPDL tRSTH
tREC DS1923
RESISTOR
After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to VPUP through the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold VTH is crossed, the DS1923 waits for tPDH and then transmits a Presence Pulse by pulling the line low for tPDL. To detect a presence pulse, the master must test the logical state of the 1-Wire line at tMSP. The tRSTH window must be at least the sum of tPDHMAX, tPDLMAX, and tRECMIN. Immediately after tRSTH is expired, the DS1923 is ready for data communication. In a mixed population network tRSTH should be extended to minimum 480s at standard speed and 48s at Overdrive speed to accommodate other 1-Wire devices.
Read/Write Time Slots
Data communication with the DS1923 takes place in time slots, which carry a single bit each. Write time slots transport data from bus master to slave. Read time slots transfer data from slave to master. The definitions of the write and read time slots are illustrated in Figure 13. All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the threshold VTL, the DS1923 starts its internal timing generator that determines when the data line is sampled during a write time slot and how long data will be valid during a read-time slot.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Master-to-Slave
For a write-one time slot, the voltage on the data line must have crossed the VTH threshold before the write-one low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below the VTH threshold until the write-zero low time tW0LMIN is expired. The voltage on the data line should not exceed VILMAX during the entire tW0L or tW1L window. After the VTH threshold has been crossed, the DS1923 needs a recovery time tREC before it is ready for the next time slot.
Figure 13. READ/WRITE TIMING DIAGRAM
Write-One Time Slot
VPUP tW1L
VIHMASTER VTH
VTL VILMAX 0V
tF RESISTOR
e
tSLOT MASTER
Write-Zero Time Slot
VPUP tW0L
VIHMASTER VTH
VTL VILMAX 0V
tF RESISTOR
tSLOT MASTER
tREC
Read-Data Time Slot
VPUP VIHMASTER VTH VTL VILMAX 0V tF RESISTOR d tRL tMSR Master Sampling Window tREC tSLOT MASTER DS1923
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Slave-to-Master
A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below VTL until the read-low time tRL is expired. During the tRL window, when responding with a 0, the DS1923 starts pulling the data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again. When responding with a 1, the DS1923 does not hold the data line low at all, and the voltage starts rising as soon as tRL is over. The sum of tRL + d (rise rime) on one side and the internal timing generator of the DS1923 on the other side define the master sampling window (tMSRMIN to tMSRMAX) in which the master must perform a read from the data line. For most reliable communication, tRL should be as short as permissible and the master should read close to but no later than tMSRMAX. After reading from the data line, the master must wait until tSLOT is expired. This guarantees sufficient recovery time tREC for the DS1923 to get ready for the next time slot.
Improved Network Behavior
In a 1-Wire environment line termination is possible only during transients controlled by the bus master (1-Wire driver). 1-Wire networks, therefore are susceptible to noise of various origins. Depending on the physical size and topology of the network, reflections from end points and branch points can add up or cancel each other to some extent. Such reflections are visible as glitches or ringing on the 1-Wire communication line. Noise coupled onto the 1-Wire line from external sources can also result in signal glitching. A glitch during the rising edge of a time slot can cause a slave device to lose synchronization with the master and, as a consequence, result in a search ROM command coming to a dead end or cause a device-specific function command to abort. For better performance in network applications, the DS1923 uses a new 1-Wire front end, which makes it less sensitive to noise and also reduces the magnitude of noise injected by the slave device itself. The 1-Wire front end of the DS1923 differs from traditional slave devices in four characteristics. 1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to the line impedance than a digitally switched transistor, converting the high-frequency ringing known from traditional devices into a smoother low-bandwidth transition. The slew-rate control is specified by the parameter tFPD, which has different values for standard and Overdrive speed. 2) There is additional low-pass filtering in the circuit that detects the falling edge at the beginning of a time slot. This reduces the sensitivity to high-frequency noise. This additional filtering does not apply at Overdrive speed. 3) There is a hysteresis at the low-to-high switching threshold VTH. If a negative glitch crosses VTH but does not go below VTH - VHY, it will not be recognized (Figure 14, Case A). The hysteresis is effective at any 1-Wire speed. 4) There is a time window specified by the rising edge hold-off time tREH during which glitches are ignored, even if they extend below VTH - VHY threshold (Figure 14, Case B, tGL < tREH). Deep-voltage droops or glitches that appear late after crossing the VTH threshold and extend beyond the tREH window cannot be filtered out and are taken as beginning of a new time slot (Figure 14, Case C, tGL tREH). Only devices that have the parameters tFPD, VHY, and tREH specified in their electrical characteristics use the improved 1-Wire front end.
Figure 14. NOISE SUPPRESSION SCHEME
VPUP VTH VHY Case A 0V Case B tGL Case C tGL tREH tREH
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
CRC GENERATION
With the DS1923 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an 8-bit type and is stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC value from the first 56 bits of the 64-bit ROM and compare it to the value stored within the DS1923 to determine if the ROM data 8 5 4 has been received error-free. The equivalent polynomial function of this CRC is: X + X + X + 1. This 8-bit CRC is received in the true (noninverted) form. It is computed at the factory and lasered into the ROM. The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x + x + x + 1. This CRC is used for error detection when reading register pages or the data log memory using the Read Memory with CRC command and for fast verification of a data transfer when writing to or reading from the scratchpad. In contrast to the 8-bit CRC, the 16-bit CRC is always communicated in the inverted form. A CRC generator inside the DS1923 (Figure 15) calculates a new 16-bit CRC as shown in the command flow chart of Figure 9. The bus master compares the CRC value read from the device to the one it calculates from the data and decides whether to continue with an operation or to reread the portion of the data with the CRC error. With the initial pass through the Read Memory with CRC flow chart, the 16-bit CRC value is the result of shifting the command byte into the cleared CRC generator, followed by the 2 address bytes and the data bytes. The password is excluded from the CRC calculation. Subsequent passes through the Read Memory with CRC flow chart generate a 16-bit CRC that is the result of clearing the CRC generator and then shifting in the data bytes. With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in the command code, the Target Addresses, TA1 and TA2, and all the data bytes. The DS1923 transmits this CRC only if the data bytes written to the scratchpad include scratchpad ending offset 11111b. The data can start at any location within the scratchpad. With the Read Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in the command code, the Target Addresses, TA1 and TA2, the E/S byte, and the scratchpad data starting at the target address. The DS1923 transmits this CRC only if the reading continues through the end of the scratchpad, regardless of the actual ending offset. For more information on generating CRC values see the Dallas Application Note 27.
16 15 2
Figure 15. CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL
Polynomial = X
1 STAGE
st
16
+X
15
+X +1
6 STAGE
th
2
2 STAGE
nd
3 STAGE
rd
4 STAGE
th
5 STAGE
th
7 STAGE
th
8 STAGE
th
X
0
X
1
X
2
X
3
X
4
X
5
X
6
X
7
9 STAGE
th
10 STAGE
th
11 STAGE
10
th
12 STAGE
th
13 STAGE
th
14 STAGE
th
15 STAGE
14
th
16 STAGE
th
X
8
X
9
X
X
11
X
12
X
13
X
X
15
X
16
INPUT DATA
CRC OUTPUT
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Command-Specific 1-Wire Communication Protocol--Legend
Symbol RST PD Select WS RS CPS RMC CM FC SM STP TA TA-E/S <32 bytes> FFh CRC16\ FF loop AA loop Description 1-Wire Reset Pulse generated by master 1-Wire Presence Pulse generated by slave Command and data to satisfy the ROM function protocol Command "Write Scratchpad" Command "Read Scratchpad" Command "Copy Scratchpad with Password" Command "Read Memory with Password & CRC" Command "Clear Memory with Password " Command "Forced Conversion" Command "Start Mission with Password" Command "Stop Mission with Password" Target Address TA1, TA2 Target Address TA1, TA2 with E/S byte Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh Transfer of as many data bytes as are needed to reach the end of a memory page Transfer of as many data bytes as are needed to reach the end of the data log memory Transfer of 8 bytes that either represent a valid password or acceptable dummy data Transfer of 32 bytes Transfer of an undetermined amount of data Transmission of one byte FFh Transfer of an inverted CRC16 Indefinite loop where the master reads FF bytes Indefinite loop where the master reads AA bytes
Command-Specific 1-Wire Communication Protocol--Color Codes
Master to slave Slave to master
Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)
RST PD Select WS TA CRC16\ FF loop
Read Scratchpad (Cannot Fail)
RST PD Select RS TA-E/S CRC16\ FF loop
Copy Scratchpad with Password (Success)
RST PD Select CPS TA-E/S AA loop
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Copy Scratchpad with Password (Fail TA-E/S or Password)
RST PD Select CPS TA-E/S FF loop
Read Memory with Password and CRC (Success)
RST PD Select RMC TA CRC16\
<32 bytes>
CRC16\
FF loop Loop
Read Memory with Password and CRC (Fail Password or Address)
RST PD Select RMC TA FF loop
Clear Memory with Password
RST PD Select CM FFh FF loop
To verify success, read the General Status Register at address 0215h. If MEMCLR is 1, the command was executed successfully.
Forced Conversion
RST PD Select FC FFh FF loop
To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Sample Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully.
Start Mission with Password
RST PD Select SM FFh FF loop
To verify success, read the General Status Register at address 0215h. If MIP is 1 and MEMCLR is 0, the command was executed successfully.
Stop Mission with Password
RST PD Select STP FFh FF loop
To verify success, read the General Status Register at address 0215h. If MIP is 0, the command was executed successfully.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
MISSION EXAMPLE: PREPARE AND START A NEW MISSION
Assumption: The previous mission has been ended by using the Stop Mission command. Passwords are not enabled. The device is a DS1923. Starting a mission requires three steps: Step 1: clear the data of the previous mission Step 2: write the setup data to register page 1 Step 3: start the mission
STEP 1
Clear the previous mission. With only a single device connected to the bus master, the communication of step 1 looks like this: MASTER MODE TX RX TX TX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 96h <8 FFh bytes> FFh (Reset) (Presence) COMMENTS Reset pulse Presence pulse Issue "skip ROM" command Issue "clear memory" command Send dummy password Send dummy byte Reset pulse Presence pulse
STEP 2
During the setup, the device needs to learn the following information: Time and Date Sample Rate Alarm Thresholds Alarm Controls (Response to Conditional Search) General Mission Parameters (e.g., Channels to Log and Logging Format, Rollover, Start Mode) Mission Start Delay The following data will setup the DS1923 for a mission that logs temperature and humidity using 8-bit format for both. Such a mission could last up to 28 days until the 8192-byte data log memory is full. ADDRESS 0200h 0201h 0202h 0203h 0204h 0205h 0206h 0207h 0208h 0209h 020Ah 020Bh 020Ch 020Dh 020Eh 020Fh DATA 00h 30h 15h 15h 05h 04h 0Ah 00h 66h 7Ah 6Fh 9Eh FFh FFh FFh FFh EXAMPLE VALUES 15:30:00 hours Time FUNCTION
15 of May in 2004 Every 10 minutes (EHSS = 0) 10C low 20C high 40%RH low 70%RH high (don't care)
th
Date Sample rate Temperature alarm Threshold Humidity alarm threshold, No software correction used Clock through Read-only registers
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ADDRESS 0210h 0211h 0212h 0213h 0214h 0215h 0216h 0217h 0218h
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory DATA EXAMPLE VALUES FUNCTION 03h Enable high and low alarm Temperature Alarm Control FFh Enable high and low alarm Humidity Alarm Control 01h On (enabled), EHSS = 0 (low sample rate) RTC oscillator control, sample rate selection C3h Normal start; no rollover; 8-bit logging General mission control FFh (don't care) Clock through FFh Read-only registers 5Ah 00h 90 minutes Mission start delay 00h
With only a single device connected to the bus master, the communication of step 2 looks like this: MASTER MODE TX RX TX TX TX TX TX TX TX RX TX TX RX RX RX RX TX RX TX TX TX TX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 0Fh 00h 02h <25 data bytes> <7 FFh bytes> (Reset) (Presence) CCh AAh 00h 02h 1Fh <32 data bytes> (Reset) (Presence) CCh 99h 00h 02h 1Fh <8 FFh bytes> (Reset) (Presence) COMMENTS Reset pulse Presence pulse Issue "skip ROM" command Issue "write scratchpad" command TA1, beginning offset=00h TA2, address=0200h Write 25 bytes of data to scratchpad Write through the end of the scratchpad Reset pulse Presence pulse Issue "skip ROM" command Issue "read scratchpad" command Read TA1, beginning offset=00h Read TA2, address=0200h Read E/S, ending offset=1Fh, flags=0h Read scratchpad data and verify Reset pulse Presence pulse Issue "skip ROM" command Issue "copy scratchpad" command TA1 TA2 (AUTHORIZATION CODE) E/S Send dummy password Reset pulse Presence pulse
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
STEP 3
Start the new mission. With only a single device connected to the bus master, the communication of step 3 looks like this: MASTER MODE DATA (LSB FIRST) COMMENTS TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue "skip ROM" command TX CCh Issue "start mission" command TX <8 FFh bytes> Send dummy password TX FFh Send dummy byte TX (Reset) Reset pulse RX (Presence) Presence pulse If step 3 was successful, the MIP bit in the General Status Register will be 1, the MEMCLR bit will be 0 and the mission start delay will count down.
SOFTWARE CORRECTION ALGORITHM FOR TEMPERATURE
The accuracy of high-resolution temperature conversion results (forced conversion as well as temperature logs) can be improved through a correction algorithm. The data needed for this software correction is stored in the calibration memory (memory page 18). It consists of reference temperature (Tr) and conversion result (Tc) for two different temperatures, as shown below. See section Temperature Conversion for the binary number format. ADDRESS 0240h 0241h 0242h 0243h 0244h 0245h 0246h 0247h DESIGNATOR Tr2H Tr2L Tc2H Tc2L Tr3H Tr3L Tc3H Tc3L DESCRIPTION Cold reference temperature, high-byte Cold reference temperature, low-byte Conversion result at cold reference temperature, high-byte Conversion result at cold reference temperature, low-byte Hot reference temperature, high-byte Hot reference temperature, low-byte Conversion result at hot reference temperature, high-byte Conversion result at hot reference temperature, low-byte
The software correction algorithm requires two additional values, which are not stored in the device. For the DS1923 these values are Tr1 = 60C and Offset = 41. The correction algorithm consists of two steps, preparation and execution. The preparation step first converts temperature data from binary to decimal C format. Next three coefficients A, B, and C are computed. In the execution step the temperature reading as delivered by the DS1923 is first converted from the low/high-byte format (TcL, TcH) to C (Tc) and then corrected to Tcorr. Once step 1 is performed, the three coefficients can be used repeatedly to correct any temperature reading and temperature log of the same device.
Step 1. Preparation
Tr1 = 60 Offset = 41 Tr2 = Tr2H/2 + Tr2L/512 - Offset (convert from binary to C) Tr3 = Tr3H/2 + Tr3L/512 - Offset (convert from binary to C) Tc2 = Tc2H/2 + Tc2L/512 - Offset (convert from binary to C) Tc3 = Tc3H/2 + Tc3L/512 - Offset (convert from binary to C) Err2 = Tc2 - Tr2 Err3 = Tc3 - Tr3 Err1 = Err2 2 2 2 2 2 2 B = (Tr2 - Tr1 ) * (Err3 - Err1)/[(Tr2 - Tr1 ) * (Tr3 - Tr1) + (Tr3 - Tr1 ) * (Tr1 - Tr2)] 2 2 A = B * (Tr1 - Tr2) / (Tr2 - Tr1 ) 2 C = Err1 - A * Tr1 - B * Tr1 48 of 52
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Step 2. Execution
Tc = TcH/2 + TcL/512 - Offset 2 Tcorr = Tc - (A * Tc + B * Tc + C) (convert from binary to C) (the actual correction)
Numerical Correction Example
Converted Data from Calibration Memory Tr2 = -10.1297C Tr3 = 24.6483C Tc2 = -10.0625C Tc3 = 24.5C Resulting Correction Coefficients B = -0.008741 A = 0.000175/C C = -0.039332C Error Values Err2 = 0.0672C Err3 = -0.1483C Err1 = Err2 Application of Correction Coefficients to Sample Reading Tc = 22.500000C Tcorr = 22.647275C
NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are found on various websites and are included in cross-compilers.
SOFTWARE CORRECTION ALGORITHM FOR HUMIDITY
The accuracy of humidity conversion results (forced conversion as well as logged data) can be improved through a correction algorithm. The data needed for this software correction is stored in the calibration memory (memory page 18). It consists of reference humidity (Hr) and conversion result (Hc) for three different humidity levels, as shown below. The data is taken at 25C. Address 0248h 0249h 024Ah 024Bh 024Ch 024Dh 024Eh 024Fh 0250h 0251h 0252h 0253h Designator Hr1H Hr1L Hc1H Hc1L Hr2H Hr2L Hc2H Hc2L Hr3H Hr3L Hc3H Hc3L Description Low reference humidity, high-byte Low reference humidity, low-byte Conversion result at low reference humidity, high-byte Conversion result at low reference humidity, low-byte Medium reference humidity, high-byte Medium reference humidity, low-byte Conversion result at medium reference humidity, high-byte Conversion result at medium reference humidity, low-byte High reference humidity, high-byte High reference humidity, low-byte Conversion result at high reference humidity, high-byte Conversion result at high reference humidity, low-byte
The correction algorithm consists of two steps: preparation and execution. The preparation step first converts humidity data from binary to decimal %RH format. Next three coefficients A, B, and C are computed. In the execution step the humidity reading as delivered by the DS1923 (raw data) is first converted from the low/high-byte format (HcL, HcH) to %RH (Hc) and then corrected to Hcorr. Once step 1 is performed, the three coefficients can be used repeatedly to correct any humidity reading and humidity log of the same device.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Step 1. Preparation
For the humidity data in the calibration memory, the lower four bits of each low byte are set to 0. This simplifies the conversion from the binary data format to raw %RH values to a one-line equation. Hr1 = ((Hr1H * 256 + Hr1L) * 5.02/65536 - 0.958)/0.0307 Hr2 = ((Hr2H * 256 + Hr2L) * 5.02/65536 - 0.958)/0.0307 Hr3 = ((Hr3H * 256 + Hr3L) * 5.02/65536 - 0.958)/0.0307 Hc1 = ((Hc1H * 256 + Hc1L) * 5.02/65536 - 0.958)/0.0307 Hc2 = ((Hc2H * 256 + Hc2L) * 5.02/65536 - 0.958)/0.0307 Hc3 = ((Hc3H * 256 + Hc3L) * 5.02/65536 - 0.958)/0.0307 Err1 = Hc1 - Hr1 Err2 = Hc2 - Hr2 Err3 = Hc3 - Hr3 B= A= C= [(Hr2 - Hr1 ) * (Err3 - Err1) + Hr3*(Err1 - Err2) + Hr1 * (Err2 - Err1)]/[(Hr2 - Hr1 ) * (Hr3 - Hr1) + (Hr3 2 Hr1 ) * (Hr1 - Hr2)] 2 2 [Err2 - Err1 + B * (Hr1 - Hr2)] / (Hr2 - Hr1 ) 2 Err1 - A * Hr1 - B * Hr1
2 2 2 2 2
(convert from binary to %RH)
Step 2. Execution
Hc = ((HcH * 256 + HcL) * 5.02/65536 - 0.958)/0.0307 2 Hcorr = Hc - (A * Hc + B * Hc + C) (convert from binary to %RH) (the actual correction)
Numerical Correction Example
Converted Data from Calibration Memory Hr1 = 20%RH Hr2 = 60%RH Hr3 = 90%RH Hc1 = 17.65%RH Hc2 = 56.41%RH Hc3 = 89.57%RH Resulting Correction Coefficients B = -0.186810 A = 0.001948/%RH C = 0.607143%RH Error Values Err1 = -2.35%RH Err2 = -3.59%RH Err3 = -0.43%RH
Application of Correction Coefficients to Sample Reading Hc = 8.9%RH Hcorr = 9.8%RH
NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are found on various websites and are included in cross-compilers.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
RH TEMPERATURE COMPENSATION
The data for the software correction of humidity is taken at 25C. Since the temperature characteristics of the humidity sensor are known, humidity readings taken at other temperatures can be corrected, provided the temperature at the time of the humidity conversion is also known. Therefore, to obtain the most accurate humidity results, both temperature and humidity should be logged. Temperature compensation uses the following equation: HTcorr = (Hcorr * K + a*(T-25C) - b*(T-25C))/(K + g*(T-25C)- d*(T-25C)) Hcorr is the humidity reading with the software correction algorithm for humidity already applied, as explained in the previous section. The function and values of the other parameters are explained in the table below. Name T K a b g d Function Temperature at the time of humidity conversion Humidity sensor conversion constant Linear compensation, enumerator Quadratic compensation, enumerator Linear compensation, denominator Quadratic compensation, denominator Value (in C) 0.0307 0.0035/C 0.000043/C >15C: 0.00001/C 15C: -0.00005/C 0.000002/C
Numerical Temperature Compensation Example
Sample Input Data T = 70C Hcorr = 24.445%RH Application of Correction Coefficients to Sample Reading g = 0.00001/C HTcorr = (24.445 * 0.0307 + 0.0035 * 45 - 0.000043 * 45)/ (0.0307 + 0.00001 * 45 - 0.000002 * 45) HTcorr = 30.291 %
SOFTWARE SATURATION DRIFT COMPENSATION
Capacitive humidity sensors read higher humidity values than the actual humidity level when they are exposed to a high-humidity environment for an extended time period. The DS1923's humidity sensor produces readings that are higher than the actual humidity when exposed to humidity levels of about 70%RH and higher. This shift continues to increase while the device remains at 70%RH and above. This effect is called saturation drift, or sometimes referred to as hyteresis. This drift is reversible. Readings return to their regular level when the DS1923 is removed from a high-humidity environment. It is possible to compensate for most of the error introduced by the saturation drift by post-processing temperature and humidity logs using the equation below, which is based on laboratory tests and curve-fitting techniques.
HScorr = HTcorr -
k=1 th ARHk The average software corrected and temperature compensated humidity reading of the k hour that the device is continuously exposed to 70%RH or higher. th Tk The average software corrected temperature reading of the k hour that the device is continuously exposed to 70%RH or higher. N The number of hours that the device is continuously exposed to 70%RH or higher. th HTcorr The humidity reading at the end of the N hour with the software correction algorithm for humidity and temperature compensation already applied. See previous sections for details. The numbers in the equation are derived from curve fitting. They apply to a time scale in hours.
S
N
0.0156 * ARHk * 2.54 1 + (Tk - 25) / 100
-0.3502*k
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Numerical Saturation Drift Compensation Example
Sample Input Data (N = 8) k (hour) Tk (C) ARHk (%RH) 1 25.1 91.1 2 25.0 92.5 3 24.9 92.9 4 25.0 93.1 5 25.1 93.2 6 25.1 93.3 7 25.0 93.6 8 24.9 93.7 HTcorr = 93.70207 %RH HScorr HScorr = = = Application of Correction Algorithm Partial Corrections (individual addends) 1.024321 0.751140 0.544824 0.393535 0.283950 0.205086 0.148591 0.107428 Sum of partial corrections: 3.458875
HTcorr - Sum of partial corrections 93.70207 %RH - 3.458875%RH 90.24319%RH
The data in this example was taken from devices that were exposed for several hours to 90%RH at 25C in a test chamber. The drift per hour decreases the longer the device is exposed to high humidity. The correction algorithm compensates for the drift reasonably well. Since the error introduced by the saturation is relatively small, for some applications compensation may not be necessary.
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