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| DS1921L-F5X Thermochron iButton www.maxim-ic.com SPECIAL FEATURES* Digital thermometer measures temperature in 0.5C increments (accuracy 1.0C) Built-in real-time clock (RTC) and timer has accuracy of 2 minutes per month from 0C to 45C Automatically wakes up and measures temperature at user-programmable intervals from 1 to 255 minutes Logs up to 2048 consecutive temperature measurements in protected nonvolatile (NV) memory Records a long-term temperature histogram with 2.0C resolution Programmable temperature-high and temperature-low alarm trip points Records up to 24 time stamps and durations when temperature leaves the range specified by the trip points 512 bytes of general-purpose read/write NV memory Typical lifetime more than 9 years Communicates to host with a single digital signal at 14.1kbits or 125kbits per second using 1-Wire(R) protocol 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) F5 MICROCAN 5.89 0.36 0.51 (c) 1993 16.25 RR YYWW REGISTERED xx 21 17.35 15C000FBC52B IO GND All dimensions are shown in millimeters. COMMON iButton FEATURES Digital identification and information by momentary contact Unique, factory-lasered and tested 64-bit registration number (8-bit family code + 48-bit serial number + 8-bit CRC tester) assures absolute traceability because no two parts are alike 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 ORDERING INFORMATION DS1921L-F51 DS1921L-F52 DS1921L-F53 DS1921L-F50 -10C to +85C -20C to +85C -30C to +85C -40C to +85C F5 iButton(R) F5 iButton F5 iButton F5 iButton EXAMPLES OF ACCESSORIES DS9096P DS9101 DS9093RA DS9093A DS9092 Self-Stick Adhesive Pad Multi-Purpose Clip Mounting Lock Ring Snap-In Fob iButton Probe 1-Wire, Microcan, and iButton are registered trademarks of Dallas Semiconductor *See ELECTRICAL CHARACTERISTICS table for details. 1 of 40 121003 DS1921L iButton DESCRIPTION The DS1921L Thermochron iButtons are rugged, self-sufficient systems that measure temperature and record the result in a protected memory section. The recording is done at a user-defined rate, both as a direct storage of temperature values as well as in the form of a histogram. Up to 2048 temperature values taken at equidistant intervals ranging from 1 to 255 minutes can be stored. The histogram provides 63 data bins for a resolution of 2.0C. If the temperature leaves a user-programmable range, the DS1921L will also record when this happened, for how long the temperature stayed outside the permitted range, and if the temperature was too high or too low. An additional 512 bytes of read/write NV memory allow storing information pertaining to the object to which the DS1921L is associated. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. Every DS1921L 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 DS1921L to be mounted on almost any object, including containers, pallets, and bags. APPLICATION The DS1921L Thermochron iButton is an ideal device to monitor the temperature of any object it is attached to or shipped with, such as perishable goods or containers of temperature sensitive chemicals. Using TMEX, the read/write NV memory can store an electronic copy of shipping information, date of manufacture and other important data written as clear as well as encrypted files. OVERVIEW The block diagram in Figure 1 shows the relationships between the major control and memory sections of the DS1921L. The device has seven main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 4096-bit general-purpose SRAM, 4) 256-bit register page of timekeeping, control, and counter registers, 5) 96 bytes of alarm time stamp and duration logging memory, 6) 126 bytes of histogram memory, and 7) 2048 bytes of data-logging memory. Except for the ROM and the scratchpad, all other memory is arranged in a single linear address space. All memory reserved for logging purposes, counter registers and several other registers are read-only for the user. The timekeeping and control registers are write-protected while the device is programmed for a mission. The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one of the seven ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5) Skip ROM, 6) Overdrive-Skip ROM or 7) Overdrive-Match ROM. Upon completion of an Overdrive ROM command byte executed at standard speed, the device will enter Overdrive mode, where all subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is described in Figure 12. After a ROM function command is successfully executed, the memory functions become accessible and the master may provide any one of the seven available commands. The protocol for these memory function commands is described in Figure 10. All data is read and written least significant bit first. 2 of 40 DS1921L DS1921L BLOCK DIAGRAM Figure 1 1-Wire Port IO ROM Function Control 64-Bit Lasered ROM Parasite Powered Circuitry Memory Function Control 256-Bit Scratchpad General-Purpose SRAM 32.768kHz Oscillator Internal Timekeeping & Control Reg. & Counters Register Page Alarm Time Stamp and Duration Logging Memory Temperature Sensor Control Logic Histogram Memory 3V Lithium Datalog Memory PARASITE POWER The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry "steals" power whenever the IO input is high. IO will provide 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, lithium is conserved, and 2) if the lithium is exhausted for any reason, the ROM may still be read normally. 64-BIT LASERED ROM Each DS1921L contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 36 bits are a unique serial number. The next 12 bits, called temperature range code, allow distinguishing the various DS1921L-F5 versions from each other and from the DS1921H and DS1921Z. The last eight bits are a CRC of the first 56 bits. See Figure 3 for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 4. The polynomial is X8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is available in Application Note 27 and in the Book of DS19xx iButton Standards. 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 eighth 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 eight bits of CRC returns the shift register to all 0s. 3 of 40 DS1921L HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL Figure 2 BUS Master 1-Wire net Other Devices DS1921 Command Level: Available Commands: Read ROM Match ROM Search ROM Skip ROM Overdrive Skip Overdrive Match Conditional Search ROM Write Scratchpad Read Scratchpad Copy Scratchpad Read Memory Read Memory w/CRC Clear Memory Cmd. Data Field Codes: Affected: 33h 55h F0h CCh 3Ch 69h ECh 64-bit Reg. # 64-bit Reg. # 64-bit Reg. # N/A OD-Flag 64-bit Reg. #, OD-Flag 64-bit Reg. #, Cond. Search settings, device status 256-bit scratchpad, flags 256-bit scratchpad 4096-bit SRAM, registers, flags All memory All memory Mission Time Stamp, Mission Samples Counter, Start Delay, Sample Rate, Alarm Time Stamps and Durations, Histogram Memory Memory address 211h 1-Wire ROM Function Commands DS1921-specific Memory Function Commands 0Fh AAh 55h F0h A5h 3Ch Convert Temperature 44h 64-BIT LASERED ROM Figure 3 MSB 8-Bit CRC Code MSB DEVICE DS1921L-F51 DS1921L-F52 DS1921L-F53 DS1921L-F50 DS1921H-F5 DS1921Z-F5 LSB 12-Bit Temperature Range Code MSB TEMP. RANGE (C) -10 to +85 -20 to +85 -30 to +85 -40 to +85 +15 to +46 -5 to +26 LSB MSB 36-Bit Serial Number LSB TEMP. RANGE CODE 0011 0010 0001 0000 0100 0011 0100 0101 0101 0110 1111 1011 1100 0100 1100 0100 0010 0010 LSB 8-Bit Family Code (21h) MSB LSB RESOLUTION (C) 0.5 0.5 0.5 0.5 0.125 0.125 HEX. EQUIVALENT 34C 254 15C 064 4F2 3B2 4 of 40 DS1921L 1-Wire CRC GENERATOR Figure 4 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 MEMORY The memory map of the DS1921L is shown in Figure 5. The 4096-bit general-purpose SRAM make up pages 0 through 15. The timekeeping, control, and counter registers fill page 16, called Register Page (see Figure 6). Pages 17 to 19 are assigned to storing the alarm time stamps and durations. The temperature histogram bins begin at page 64 and use up to four pages. The temperature logging memory covers pages 128 to 191. Memory pages 20 to 63, 68 to 127, and 192 to 255 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 memory pages 17 and higher are read-only for the user. They are written to or erased solely under supervision of the on-chip control logic. DS1921L MEMORY MAP Figure 5 32-Byte Intermediate Storage Scratchpad ADDRESS 0000h to 01FFh 0200h to 021Fh 0220h to 027Fh 0280h to 07FFh 0800h to 087Fh 0880h to 0FFFh 1000h to 17FFh 1800h to 1FFFh General-Purpose SRAM (16 Pages) 32-Byte Register Page Alarm Time Stamps and Durations (Reserved for Future Extensions) Temperature Histogram Memory (Reserved for Future Extensions) Datalog Memory (64 Pages) (Reserved for Future Extensions) Pages 0 to 15 Page 16 Pages 17 to 19 Pages 20 to 63 Pages 64 to 67 Pages 68 to 127 Pages 128 to 191 Pages 192 to 255 5 of 40 DS1921L DS1921L REGISTER PAGE MAP Figure 6 ADDRESS RANGE 0200h to 0206h 0207h to 020Ah 020Bh 020Ch 020Dh 020Eh 020Fh to 0210h 0211h 0212h to 0213h 0214h 0215h to 0219h 021Ah to 021Ch 021Dh to 021Fh ACCESS TYPE* R/W; R** R/W; R** R/W; R** R/W; R** R/W; R** R/W; R** R; R** R; R** R/W; R** R/W; R/W R; R R; R R; R DESCRIPTION RTC Registers RTC Alarm Temperature Low Alarm Threshold Temperature High Alarm Threshold Sample Rate Control Register (no function; will read 00h) Forced Temperature Conversion Readout Mission Start Delay Status Register Mission Time Stamp Mission Samples Counter Device Samples Counter *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. **While a mission is in progress, these addresses can be read. The first write-attempt, however, will end the mission, but not overwrite any settings. TIMEKEEPING The RTC/alarm and calendar information is accessed by reading/writing the appropriate bytes in the register page, address 200h to 206h. Note that some bits are set to 0. These bits will always read 0 regardless of how they are written. The contents of the time, calendar, and alarm registers are in the Binary-Coded Decimal (BCD) format. RTC and RTC Alarm Register Bitmap ADDR 0200h 0201h 0202h 0203h 0204h 0205h 0206h 0207h 0208h 0209h 020Ah b7 0 0 0 0 0 CENT MS MM MH MD b5 b4 10 Seconds 10 Minutes 12/24 20h. 10h. AM/PM b6 b3 b2 b1 Single Seconds Single Minutes Single Hours b0 0 0 0 0 10 Date 0 0 10m. 10 Years 10 Seconds Alarm 10 Minutes Alarm 12/24 10ha. 10h. A/P alm. 0 0 0 0 Day of Week Single Date Single Months Single Years Single Seconds Alarm Single Minutes Alarm Single Hours Alarm 0 Day of Week Alarm 6 of 40 DS1921L RTC/Calendar The RTC of the DS1921L 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 20hour bit (20 to 23 hours). To distinguish between the days of the week the DS1921L includes a counter with a range from 1 to 7. The assignment of counter value to the day of week is arbitrary. Typically, the number 1 is assigned to a Sunday (U.S. standard) or to a Monday (European standard). 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. The DS1921L is Y2K-compliant. Bit 7 (CENT) of the Months Register at address 205h serves as a century flag. When the Year Register rolls over from 99 to 00 the century flag will toggle. It is recommended to write the century bit to a 1 when setting the RTC to a time/date between the years 2000 and 2099. RTC Alarms The DS1921L also contains a RTC alarm function. The alarm registers are located in registers 207h to 20Ah. The most significant bit of each of the alarm registers is a mask bit. When all of the mask bits are logic 0, an alarm will occur once per week when the values stored in timekeeping registers 200h to 203h match the values stored in the time of day alarm registers. Any alarm will set the Timer Alarm Flag (TAF) in the device's Status Register (address 214h). The bus master may set the Search Conditions in the Control Register (address 20Eh) to identify devices with timer alarms by means of the Conditional Search function (see ROM Function Commands). RTC Alarm Control ALARM REGISTER MASK BITS (Bit 7 of 207h to 20Ah) MS 1 0 0 0 0 MM 1 1 0 0 0 MH 1 1 1 0 0 MD 1 1 1 1 0 Alarm once per second. Alarm when seconds match (once per minute). Alarm when minutes and seconds match (once every hour). Alarm when hours, minutes and seconds match (once every day). Alarm when day, hours, minutes, and seconds match (once every week). Temperature Conversion The DS1921L measures temperatures with a resolution of 0.5 Celsius. Temperature values are represented in a single byte as an unsigned binary number, which translates into a theoretical range of 128C. The range, however, has been limited to values from 0000 0000 (00h) through 1111 1010 (FAh). The codes 01h to F9h are considered valid temperature readings. 7 of 40 DS1921L If a temperature conversion yields a temperature that is out-of-range, it will be recorded as 00h (if too low) or FAh (if too high). Since out-of-range results are accumulated in histogram bins 0 and 62 (see section Temperature Logging and Histogram) the data in these bins is of limited value. For this reason the specified temperature range of the DS1921L is considered to begin at code 04h and end at code F7h, which corresponds to histogram bins 1 to 61. With T[7..0] representing the decimal equivalent of a temperature reading, the temperature value is calculated as J (C) = T[7...0] / 2 - 40.0 This equation is valid for converting temperature readings stored in the datalog memory as well as for data read from the forced temperature conversion readout Register (address 211h). To specify the high or low temperature alarm thresholds, this equation needs to be resolved to T[7...0] = 2 * J (C) + 80.0 A value of 23C, for example, thus translates into 126 decimal or 7Eh. This corresponds to the binary patterns 0111 1110, which could be written to a Temperature Alarm Register (address 020Bh and 020Ch, respectively). Temperature Alarm Register Map ADDR 020Bh 020Ch b7 b6 b5 b4 b3 b2 Temperature Low Alarm Threshold Temperature High Alarm Threshold b1 b0 Sample Rate The content of the Sample Rate Register (address 020Dh) determines how many minutes the temperature conversions are apart from each other during a mission. The sample rate may be any value from 1 to 255, coded as an unsigned 8-bit binary number. If the memory has been cleared (Status Register bit MEMCLR = 1) and a mission is enabled (Status Register bit EM = 0), writing a non-zero value to the Sample Rate Register will start a mission. For a full description of the correct sequence of steps to start a temperaturelogging mission see sections Missioning or Missioning Example. Sample Rate Register Map ADDR 020Dh b7 b6 b5 b4 b3 Sample Rate b2 b1 b0 Control Register The DS1921L is set up for its operation by writing appropriate data to its special function registers that are located in the register page. Several functions that are controlled by a single bit only are combined into a single byte called Control Register (address 20Eh). This register can be read and written. If the device is programmed for a mission, writing to the Control Register will at the first attempt end the mission, but not overwrite any settings. Every subsequent write attempt, however, will change the register contents. 8 of 40 DS1921L Control Register Bitmap ADDR 020Eh b7 EOSC b6 EMCLR b5 0 b4 EM b3 RO b2 TLS b1 THS b0 TAS The functional assignments of the individual bits are explained in the table below. Bit 5 has no function. It always reads 0 and cannot be written to 1. Control Register Details BIT DESCRIPTION EOSC: Enable Oscillator BIT(S) b7 DEFINITION This bit controls the crystal oscillator of the RTC. When set to logic 0, the oscillator will start operation. When written to logic 1, the oscillator will stop and the device is in a low-power data retention mode. This bit must be 0 for normal operation. This bit needs to be set to logic 1 to enable the Clear Memory function, which is invoked as a memory function command. The Time-Stamp, Histogram Memory as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay and Sample Rate will be cleared only if the Clear Memory command is issued with the next access to the device. The EMCLR bit will return to 0 as the next memory function command is executed. This bit controls whether the DS1921L will begin a mission as soon as the sample rate is written. To enable the device for a mission, this bit must be 0. This bit controls whether the temperature logging memory is overwritten with new data or whether data logging is stopped once the memory is filled with data during a mission. Setting this bit to a 1 enables the rollover and data logging continues at the beginning overwriting previously collected data. Clearing this bit to 0 disables the rollover and no further temperature values will be stored in the temperature logging memory once it is filled with data. This will not stop the mission. The device will continue measuring temperatures and updating the histogram. If this bit is 1, the device will respond to a Conditional Search command if during a mission the temperature has reached or is lower than the Low Temperature Threshold stored at address 020Bh. If this bit is 1, the device will respond to a Conditional Search command if during a mission the temperature has reached or is higher than the High Temperature Threshold stored at address 020Ch. If this bit is 1, the device will respond to a Conditional Search command if during a mission a timer alarm has occurred. Since a timer alarm cannot be disabled, the TAF flag usually reads 1 during a mission. Therefore it may be advisable to set the TAS bit to a 0, in most cases. EMCLR: Memory Clear Enable b6 EM: Enable Mission RO: Rollover Enable/Disable b4 b3 TLS: Temperature Low Alarm Search THS: Temperature High Alarm Search TAS: Timer Alarm Search b2 b1 b0 Mission Start Delay The content of the Mission Start Delay register determines how many minutes will have to expire after the beginning of a mission until the first temperature measurement of the mission occurs. The delay value is stored as unsigned 16-bit integer number at addresses 212h (low byte) and 213h (high byte). The maximum delay is 65535 minutes, equivalent to 45 days, 12 hours, and 15 minutes. For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1921L to store all temperature 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. The RO bit in the control register (address 020Eh) must be set to 0 to prevent overwriting of the recorded temperature log after the datalog memory is full. 9 of 40 DS1921L Status Register The Status Register holds device status information and alarm flags. The register is located at address 214h. Writing to this register will not necessarily end a mission. Status Register Bitmap ADDR 0214h b7 TCB b6 MEMCLR b5 MIP b4 SIP b3 0 b2 TLF b1 THF b0 TAF The functional assignments of the individual bits are explained in the table below. The bits MIP, TLF, THF and THF can only be written to 0. All other bits are read-only. Bit 3 has no function. Status Register Details BIT DESCRIPTION TCB: Temperature Core Busy BIT(S) b7 DEFINITION If this bit reads 0 the DS1921L is currently performing a temperature conversion, either self-initiated because of a mission being in progress or initiated by a command when a mission is not in progress. The TCB bit goes low just before a conversion starts and returns to high just after the result is latched into the readout register at address 0211h. If this bit reads 1, the memory pages 17 and higher (alarm time stamps/durations, temperature histogram, excluding datalog memory), as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay and Sample Rate have been cleared to 0 from executing a Clear Memory function command. The MEMCLR bit will return to 0 as soon as writing a non-0 value to the Sample Rate Register starts a new mission, provided that the EM bit is also 0. The memory has to be cleared in order for a mission to start. If this bit reads 1 the DS1921L has been set up for a mission and this mission is still in progress. A mission is started if the EM bit of the Control Register (address 20Eh) is 0 and a non-zero value is written to the Sample Rate Register, address 20Dh. The MIP bit returns from logic 1 to logic 0 when a mission is ended. A mission will end with the first write attempt (Copy Scratchpad command) to any register in the address range of 200h to 213h. Alternatively, a mission can be ended by directly writing to the Status Register and setting the MIP bit to 0. The MIP bit cannot be set to 1 by writing to the status register. If this bit reads 1 the DS1921L is currently performing a temperature conversion as part of a mission in progress. The SIP bit will change from 0 to 1 approximately 250ms before the actual temperature conversion begins allowing the circuitry of the chip to wake-up. A temperature conversion including a wake-up phase takes maximum 875ms. During this time read accesses to the memory pages 17 and higher are permissible but may reveal invalid data. Logic 1 in the Temperature Low Flag bit indicates that a temperature measurement during a mission revealed a temperature equal to or lower than the value in the Temperature Low Threshold Register. The Temperature Low Flag can be cleared at any time by writing this bit to 0. Logic 1 in the Temperature High Flag bit indicates that a temperature measurement during a mission revealed a temperature equal to or higher than the value in the Temperature High Threshold Register. The Temperature High Flag can be cleared at any time by writing this bit to 0. If this bit reads 1, a RTC alarm has occurred (see section TIMEKEEPING for details). The Timer Alarm Flag can be cleared at any time by writing this bit to logic 0. Since the timer alarm cannot be disabled, the TAF flag usually reads 1 during a mission. 10 of 40 MEMCLR: Memory Cleared b6 MIP: Mission in Progress b5 SIP: Sample in Progress b4 TLF: Temperature Low Flag b2 THF: Temperature High Flag b1 TAF: Timer Alarm Flag b0 DS1921L Mission Time Stamp When a mission is started, a copy of the RTC Registers addresses 0201h, 0202h, and 0204h to 0206h is saved as the Mission Time Stamp. The Mission Time Stamp does not indicate the time of the first temperature conversion of a mission. To calculate the time of the first conversion, add to the Mission Time Stamp as many minutes as specified in the Sample Rate Register plus the value of the Mission Start Delay. Subsequent temperature conversions will take place as many minutes apart from each other as specified by the value in the Sample Rate Register. Mission samples occur on minute boundaries. Mission Time Stamp Register Bitmap ADDR 0215h 0216h 0217h 0218h 0219h b7 0 0 0 0 b6 12/24 b5 10 Minutes 20h. AM/PM b4 10h. b3 b2 b1 Single Minutes Single Hours Single Date Single Months Single Years b0 0 10 Date 0 0 10m. 10 Years Mission Samples Counter The Mission Samples Counter indicates how many temperature measurements have taken place during the current mission in progress (if MIP = 1) or during the latest mission (if MIP = 0). The value is stored as an unsigned 24-bit integer number. This counter is reset through the Clear Memory command. Mission Samples Counter Register Map ADDR 021Ah 021Bh 021Ch b7 b6 b5 b4 b3 Low Byte Center Byte High Byte b2 b1 b0 Device Samples Counter The Device Samples Counter indicates how many temperature measurements have taken place since the device was assembled at the factory. The value is stored as an unsigned 24-bit integer number. The maximum number that can be represented in this format is 16777215, which is higher than the expected lifetime of the DS1921L iButton. This counter cannot be reset under software control. Device Samples Counter Register Map ADDR 021Dh 021Eh 021Fh b7 b6 b5 b4 b3 Low Byte Center Byte High Byte b2 b1 b0 Temperature Logging and Histogram Once setup for a mission, the DS1921L logs the temperature measurements simultaneously byte after byte in the datalog memory as well as in histogram form in the histogram memory. The datalog memory is able to store 2048 temperature values measured at equidistant time points. The first temperature value of a mission is written to address location 1000h of the datalog memory, the second value to address location 1001h and so on. Knowing the starting time point (Mission Time Stamp), the interval between temperature measurements and the Mission Start Delay, one can reconstruct the time and date of each measurement. 11 of 40 DS1921L There are two alternatives to the way the DS1921L will behave after the 2048 bytes of datalog 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 byte at a time, starting again at address 1000h for the 2049th temperature value. The contents of the Mission Samples Counter (addresses 21Ah to 21Ch) in conjunction with the sample rate and the Mission Time Stamp will then allow reconstructing the time points of all values stored in the datalog memory. This gives the exact temperature history over time for the latest 2048 measurements taken. All earlier measurements cannot be reconstructed. Regardless of enabling the rollover, these values are included in the mission's temperature histogram. For the temperature histogram, the DS1921L provides 63 bins that begin at memory address 0800h. Each bin consists of a 16-bit, non-rolling-over binary counter that is incremented each time a temperature value acquired during a mission falls into the range of the bin. The least significant byte of each bin is stored at the lower address. Bin 0 begins at memory address 0800h, bin 1 at 0802h, and so on up to 087Ch for bin 62, as shown in Figure 7. The number of the bin to be updated after a temperature conversion is determined by cutting off the two least significant bits of the binary temperature value. Out of range values are range locked and counted as 00h or FAh. Histogram Bin and Temperature Cross-Reference Figure 7 TEMPERATURE READING 00h 01h 02h 03h 04h 05h 06h 07h 08h TEMP. EQUIV. IN C -40.0 or lower -39.5 -39.0 -38.5 -38.0 -37.5 -37.0 -36.5 -36.0 HISTOGRAM BIN NUMBER 0 0 0 0 1 1 1 1 2 HISTOGRAM BIN ADDRESS 800h to 801h 800h to 801h 800h to 801h 800h to 801h 802h to 803h 802h to 803h 802h to 803h 802h to 803h 804h to 805h F3h F4h F5h F6h F7h F8h F9h FAh +81.5 +82.0 +82.5 +83.0 +83.5 +84.0 +84.5 +85.0 or higher 60 61 61 61 61 62 62 62 878h to 879h 87Ah to 87Bh 87Ah to 87Bh 87Ah to 87Bh 87Ah to 87Bh 87Ch to 87Dh 87Ch to 87Dh 87Ch to 87Dh Since each data bin is 2 bytes it can increment up to 65535 times. Additional measurements for a bin that has already reached its maximum value will not be counted; the bin counter will remain at its maximum value. With the fastest sample rate of one sample every minute, a 2-byte bin is sufficient for up to 45 days if all temperature readings fall into the same bin. 12 of 40 DS1921L Temperature Alarm Logging For some applications it may be essential to not only record temperature over time and the temperature histogram, but also record when exactly the temperature has exceeded a predefined tolerance band and for how long the temperature stayed outside the desirable range. The DS1921L can log high and low durations. The tolerance band is specified by means of the Temperature Alarm Threshold Registers, addresses 20Bh and 20Ch in the register page. One can set a high and a low temperature threshold. See section Temperature Conversion for the data format the temperature has to be written in. As long as the temperature values stay within the tolerance band (i.e., are higher than the low threshold and lower than the high threshold), the DS1921L will not record any temperature alarm. If the temperature during a mission reaches or exceeds either threshold, the DS1921L will generate an alarm and set either the Temperature High Flag (THF) or the Temperature Low Flag (TLF) in the Status Register (address 214h). This way, if the search conditions (address 20Eh) are set accordingly, the master can quickly identify devices with temperature alarms by means of the Conditional Search function (see ROM Function Commands). The device also generates a time stamp of when the alarm occurred and begins recording the duration of the alarming temperature. Time stamps and durations where the temperature leaves the tolerance band are stored in the address range 0220h to 027Fh, as shown in Figure 8. This allocation allows recording 24 individual alarm events and periods (12 periods for too hot and 12 for too cold). The date and time of each of these periods can be determined from the Mission Time Stamp and the time distance between each temperature reading. Alarm Time Stamps and Durations Address Map Figure 8 ADDRESS 0220h 0221h 0222h 0223h 0224h to 0227h 0228h to 024Fh 0250h 0251h 0252h 0253h 0254h to 0257h 0258h to 027Fh DESCRIPTION Mission Samples Counter Low Byte Mission Samples Counter Center Byte Mission Samples Counter High Byte Alarm Duration Counter Alarm Time Stamp and Duration Alarm Time Stamp and Durations Mission Samples Counter Low Byte Mission Samples Counter Center Byte Mission Samples Counter High Byte Alarm Duration Counter Alarm Time Stamp and Duration Alarm Time Stamp and Durations High Alarm 2 High Alarms 3 to 12 High Alarm 1 Low Alarm 2 Low Alarms 3 to 12 Low Alarm 1 ALARM EVENT The alarm time stamp is a copy of the Mission Samples Counter when the alarm occurred. The least significant byte is stored at the lower address. One address higher than a time stamp the DS1921L maintains a 1-byte duration counter that stores the number of samples the temperature was found to be beyond the threshold. If this counter has reached its limit after 255 consecutive temperature readings and the temperature has not yet returned to within the tolerance band, the device will issue another time stamp at the next higher address and open another counter to record the duration. If the temperature returns to normal before the counter has reached its limit, the duration counter of the particular time stamp will not increment any further. Should the temperature again cross this threshold, another time stamp will be recorded and its associated counter will increment with each temperature reading outside the tolerance band. This algorithm is implemented for the low as well as for the high temperature threshold. 13 of 40 DS1921L MISSIONING The typical task of the DS1921L is recording the temperature of a temperature-sensitive object. Before the device can perform this function, it needs to be configured. This procedure is called missioning. First of all, DS1921L needs to have its RTC set to valid time and date. This reference time may be UTC (also called GMT, Greenwich Mean Time) or any other time standard that was chosen for the application. The clock must be running (EOSC = 0). Setting a RTC alarm is optional. The memory assigned to storing alarm time stamps and durations, temperature histogram, as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay and Sample Rate must be cleared using the Memory Clear command. To enable the device for a mission, the EM flag must be set to 0. These are general settings that have to be made regardless of the type of object to be monitored and the duration of the mission. Next, the low temperature and high temperature thresholds to specify the temperature tolerance band 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. The state of the Search Condition bits in the Control Register does not affect the mission. If multiple devices are connected to form a 1-Wire net, the setting of the search condition will enable devices to participate in the conditional search if certain events such as timer or temperature alarm have occurred. Details on the search conditions are found in the section ROM Function Commands later in this document and in the Control Register description. 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 recent temperature history 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 2048 to calculate the value of the sample rate (number of minutes between temperature conversions). If the estimated duration of a mission is 10 days (= 14400 minutes) for example, then the 2048-byte capacity of the datalog memory would be sufficient to store a new value every 7 minutes. If the datalog memory of the DS1921L is not large enough to store all temperature readings, one can use several devices and set the Mission Start Delay to values that make the second device start recording 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 recorded temperature log. After the RO bit and the Mission Start Delay are set, the Sample Rate Register is the last element of data that is written. The sample rate may be any value from 1 to 255, coded as an unsigned 8-bit binary number. As soon as the sample rate is written, the DS1921L will copy the current time and date into the Mission Time Stamp Register, set the MIP flag, and clear the MEMCLR flag. After as many minutes as specified by the Mission Start Delay are over, the device takes the first temperature conversion of the mission. This increments both the Mission Samples Counter and Device Samples Counter. All subsequent temperature measurements are taken on minute boundaries specified by the value in the Sample Rate Register. One may read the memory of the DS1921L to watch the mission as it progresses at any time. After the mission is started, one can read the complete register page and store the contents of the Temperature Alarm Registers up to the Device Samples Counter in encrypted form as data file in the 4096-bit SRAM section of the device. This general-purpose memory operates independently of the memory used for recording during a mission. However, do not write any of the mission-ending registers on the register page. 14 of 40 DS1921L ADDRESS REGISTERS AND TRANSFER STATUS Because of the serial data transfer, the DS1921L employs three address registers, called TA1, TA2 and E/S (Figure 9). 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. 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 will begin. This address is called byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad will store incoming data beginning at the byte offset 1Ch and will be full after only 4 bytes. The corresponding ending offset in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point to the beginning of a new page, (i.e., the byte offset will be 0). Thus, the full 32-byte capacity of the scratchpad is available, resulting also in the ending offset of 1Fh. However, it is possible to write 1 or several contiguous bytes somewhere within a page. 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. ADDRESS REGISTERS Figure 9 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 DS1921L, 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 DS1921L 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 iButton. 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 DS1921L has received these bytes, it will copy the data to the requested location beginning at the target address. 15 of 40 DS1921L MEMORY FUNCTION COMMANDS The Memory Function Flow Chart (Figure 10) describes the protocols necessary for accessing the memory and the special function registers of the DS1921L. An example on how to use these and other functions to set up the DS1921L for a mission is included at the end of this document, preceding the Electrical Characteristics section. The communication between master and DS1921L takes place either at regular speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive Mode, the DS1921L assumes regular speed. 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 ending offset (E4:E0) will be the byte offset at which the master stops writing data. Only full data bytes are accepted. If the last data byte is incomplete, its content will be ignored and the partial byte flag (PF) will be set. When executing the Write Scratchpad command, the CRC generator inside the DS1921L (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. 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. The master may end the Write Scratchpad command at any time. However, if the ending offset is 11111b, the master may send 16 read time slots and will receive the CRC generated by the DS1921L. The range 200h to 213h of the register page is write-protected during a mission. See Figure 6, Register Page Map, for the access type of the individual registers between and during missions. 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 9. Regardless of the actual ending offset, the master may read data until the end of the scratchpad after which it will receive a 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 DS1921L until a reset pulse is issued. 16 of 40 DS1921L MEMORY FUNCTION FLOW CHART Figure 10-1 Master TX Memory or Control Fkt. Command 0FH Write Scratchpad Y DS1921 sets EMCLR = 0 Master TX TA1 (T7:T0), TA2 (T15:T8) DS1921 sets Scratchpad Offset = (T4:T0) and Clears (PF, AA) Master TX Data Byte to Scratchpad Offset DS1921 sets (E4:E0) = Scratchpad Offset Y DS1921 Increments Scratchpad Offset N N From ROM Functions Flow Chart (Figure 12) AAH Read Scratchpad Y DS1921 sets EMCLR = 0 Master RX TA1 (T7:T0), TA2 (T15:T8) Master RX Ending Offset with Data Status (E/S) DS1921 sets Scratchpad Offset = (T4:T0) Master RX Data Byte from Scratchpad Offset Y To Figure 10 nd 2 Part N Master TX Reset? DS1921 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 12) From Figure 10 nd 2 Part 17 of 40 DS1921L MEMORY FUNCTION FLOW CHART Figure 10-2 From Figure 10 st 1 Part 55H Copy Scratchpad Y DS1921 sets EMCLR = 0 Master TX TA1 (T7:T0), TA2 (T15:T8) Master TX E/S Byte N F0H Read Memory Y DS1921 sets EMCLR = 0 To Figure 10 rd 3 Part N Master TX TA1 (T7:T0), TA2 (T15:T8) DS1921 sets Memory Address = (T15:T0) N DS1921 Increments Address Counter Y Master TX Reset? N Master RX Data Byte from Memory Address Authorization Code Match? Y AA = 1 DS1921 Copies Scratchpad Data to Memory N Master RX "1"s N Copying Finished Y DS1921 TX "0" Y Master RX "1"s N End of Memory? Y Master TX Reset? Y Master RX "0"s Master TX Reset? N DS1921 TX "1" N Master TX Reset? Y To Figure 10 st 1 Part From Figure 10 rd 3 Part 18 of 40 DS1921L MEMORY FUNCTION FLOW CHART Figure 10-3 From Figure 10 nd 2 Part A5H Read Mem. w/CRC Y DS1921 sets EMCLR = 0 Master TX TA1 (T7:T0), TA2 (T15:T8) DS1921 sets Memory Address = (T15:T0) N To Figure 10 th 4 Part Decision made by DS1921 Y Decision made by Master Master RX 00 Byte End of Memory? N Master RX Data Byte from Memory Address DS1921 Increments Address Counter Y Master TX Reset? N End of Page? Y Master RX CRC16 of Command, Address, Data st (1 Pass); CRC16 of Data (Subsequent Passes) CRC OK? N Master TX Reset Y N To Figure 10 nd 2 Part From Figure 10 th 4 Part 19 of 40 DS1921L MEMORY FUNCTION FLOW CHART Figure 10-4 From Figure 10 rd 3 Part 3CH Clear Memory Y N 44H Convert Temp. Y DS1921 sets EMCLR = 0 N N EMCLR = 1? Y DS1921 clears Mission Time Stamp, Mission Samples Counter, Mission Start Delay, Sample Rate Register DS1921 clears Alarm Time Stamps and Durations DS1921 clears Histogram Memory DS1921 sets MEMCLR = 1 DS1921 sets EMCLR = 0 Mission in Progress? N DS1921 sets TCB\ = 0 DS1921 Performs a Temp. Conversion DS1921 copies Result to Address 0211h DS1921 sets TCB\ = 1 Y N Master TX Reset? Y N Master TX Reset? Y N Master TX Reset? Y To Figure 10 rd 3 Part 20 of 40 DS1921L Copy Scratchpad [55h] 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). If the pattern matches, the AA (Authorization Accepted) flag will be set and the copy will begin. A pattern of alternating 1s and 0s will be 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 will be 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. Anywhere from 1 to 32 bytes may be copied to memory with this command. The AA flag will remain at logic 1 until it is cleared by the next Write Scratchpad command. Read Memory [F0h] The Read Memory command may be used to read the entire memory. After issuing the command, the master must provide the 2-byte target address. After the 2 bytes, the master reads data beginning from the target address and may continue until the end of memory, at which point logic 0s will be read. It is important to realize that the target address registers will contain the address provided. The ending offset/data status byte is unaffected. The hardware of the DS1921L provides a means to accomplish error-free writing to the memory section. To safeguard data in the 1-Wire environment when reading and to simultaneously speed up data transfers, it is recommended to packetize data into data packets of the size of one memory page each. Such a packet would typically store a 16-bit CRC with each page of data to ensure rapid, error-free data transfers that eliminate having to read a page multiple times to verify whether if the received data is correct. (See Chapter 7 of the Book of DS19xx iButton Standards or Application Note 114 for the recommended file structure.) Read Memory with CRC [A5h] The Read Memory with CRC command is used to read memory data that cannot be packetized, such as the register page and the data recorded by the device during a mission. The command works essentially the same way as the simple Read Memory, except for the 16-bit CRC that the DS1921L generates and transmits 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 2byte address (TA1 = T7:T0, TA2 = T15:T8) that indicates a starting byte location. With the subsequent read data time slots the master receives data from the DS1921L starting at the initial address and continuing until the end of a 32-byte page is reached. At that point the bus master will send 16 additional read data time slots and receive the 16-bit CRC. With subsequent read data time slots the master will receive data starting at the beginning of the next page followed again by the CRC for that page. This sequence will continue until the bus master resets the device. 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 will receive logical 0s from 21 of 40 DS1921L the DS1921L and CRC16s at page boundaries until a reset pulse is issued. The Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse. Clear Memory [3Ch] The Clear Memory command is used to clear the Sample Rate, Mission Start Delay, Mission Time Stamp, and Mission Samples Counter in the register page and the Temperature Alarm Memory and the Temperature Histogram Memory. The memory must be cleared for the device to be set up for another mission. For the Clear Memory command to function the EMCLR bit in Control Register must be set to 1. The Clear Memory command must be issued with the very next access to the device's memory functions (timed access). Issuing any other valid memory function command will reset the EMCLR bit. The Clear Memory command takes approximately 500s to complete and cannot be interrupted. However, it is possible to issue a reset/presence sequence, execute any ROM command, and access the 4096 bits of user-RAM or read the RTC or Status Register while the Clear Memory command is in progress. When the Clear Memory command is completed the MEMCLR bit in the Status Register will read 1 and the EMCLR bit will be 0. Convert Temperature [44h] If a mission is not in progress the Convert Temperature command can be issued to measure the current temperature of the device. The result of the temperature conversion will be found at memory address 211h in the register page. This command takes approximately 300ms to complete and cannot be interrupted. Memory access to any location of the device is possible while the temperature conversion takes place. 1-WIRE BUS SYSTEM The 1-Wire bus is a system that has a single bus master and one or more slaves. In all instances the DS1921L is a slave device. The bus master is typically a microcontroller or PC. For small configurations the 1-Wire communication signals can be generated under software control using a single port pin. For multi-sensor networks, the DS2480B 1-Wire line driver chip or serial port adapters based on this chip (DS9097U series) are recommended. This simplifies the hardware design and frees the microprocessor from responding in real-time. 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 DS1921L is open-drain with an internal circuit equivalent to that shown in Figure 11. 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 16.3kbits per second. The speed can be boosted to 142kbits per second by activating the Overdrive mode. The DS1921L is not guaranteed to be fully compliant to the iButton Standard. Its maximum data rate in standard speed mode is 14.1kbits per second and 125kbits per second 22 of 40 DS1921L in Overdrive. The value of the pull-up resistor primarily depends on the network size and load conditions. For most applications the optimal value of the pull-up resistor will be approximately 2.2kW. 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. With the DS1921L the bus must be left low for no longer than 15.2s at Overdrive speed to ensure that none of the slave devices on the 1-Wire bus performs a reset. Despite of its limited compliance, the DS1921L will communicate properly when used in conjunction with a DS2480B 1-Wire driver and serial port adapters that are based on this driver chip. HARDWARE CONFIGURATION Figure 11 BUS MASTER VPUP SEE TEXT DS1921 1-Wire PORT RX DATA 5 A Typ. 100 W MOSFET RX TX TX Open Drain Port Pin RX = RECEIVE TX = TRANSMIT TRANSACTION SEQUENCE The protocol for accessing the DS1921L via the 1-Wire port is as follows: Initialization ROM Function Command Memory 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 DS1921L is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section. ROM FUNCTION COMMANDS Once the bus master has detected a presence, it can issue one of the seven ROM function commands. All ROM function commands are eight bits long. A list of these commands follows (refer to flowchart in Figure 12). 23 of 40 DS1921L Read ROM [33h] This command allows the bus master to read the DS1921L's 8-bit family code, temperature range code, plus unique 36-bit serial number and 8-bit CRC. This command can only be used if there is a single DS1921L on the bus. If more than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same time (open drain will produce a wired-AND result). The resultant family code and temperature range code plus 36-bit serial number will result 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 DS1921L on a multidrop bus. Only the DS1921L that exactly matches the 64-bit ROM sequence will respond to the following memory function command. All slaves that do not match the 64-bit ROM sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the bus. 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 a Read command is issued following the Skip ROM command, data collision will occur on the bus as multiple slaves transmit simultaneously (open drain pull-downs will produce a wired-AND result). Search ROM [F0h] When a system is initially brought up, the bus master might not know the number of devices on the 1Wire bus or their 64-bit ROM codes. The Search ROM command allows the bus master to use a process of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The search ROM process is the repetition of a simple three-step routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM. After one complete pass, the bus master knows the contents of the ROM in one device. The remaining number of devices and their ROM codes may be identified by additional passes. See Chapter 5 of the Book of DS19xx iButton Standards for a comprehensive discussion of a search ROM, including an actual example. Conditional Search [ECh] The Conditional Search ROM command operates similarly to the Search ROM command except that only devices fulfilling the specified condition will participate in the search. The condition is specified by the bit functions TAS, THS, and TLS in the Control Register, address 20Eh. The Conditional Search ROM provides an efficient means for the bus master to determine devices on a multidrop system that have to signal an important event, such as a temperature leaving the tolerance band. After each pass of the conditional search that successfully determined the 64-bit ROM 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 will have dropped out of the search process and will be waiting for a reset pulse. For the conditional search, one can select any combination of the three search conditions by writing the associated bit to a logical 1. These bits correspond directly to the flags in the Status Register of the device. If the flag in the status register reads 1 and the corresponding bit in the Control Register is a logical 1 too, the device will respond to the Conditional Search command. If more than one bit search condition is selected, the first event occurring will make the device respond to the Conditional Search command. 24 of 40 DS1921L ROM FUNCTIONS FLOW CHART Figure 12-1 From Memory Functions Flow Chart (Figure 10) Master TX Reset Pulse From Figure 12 nd 2 Part OD = 0 Short Reset Pulse? Y DS1921 TX Presence Pulse Master TX ROM Function Command N 2) 1) 33H Read ROM? Y N 55H Match ROM? Y N F0H Search ROM? Y N ECH Cond. Search ROM? Y N Cond. Met? Y DS1921 TX Bit 0 DS1921 TX Bit 0 Master TX Bit 0 N Bit 0 Match? Y DS1921 TX Bit 1 DS1921 TX Bit 1 Master TX Bit 1 N Bit 1 Match? Y DS1921 TX Bit 63 1) DS1921 TX Bit 63 1) Master TX Bit 63 N Bit 63 Match? Y 1) 1) 1) 1) 1) 1) 1) To Figure 12 nd 2 Part N DS1921 TX Family Code 1 Byte 1) Master TX Bit 0 1) DS1921 TX Bit 0 DS1921 TX Bit 0 Master TX Bit 0 Bit 0 Match? Y N N Bit 0 Match? Y DS1921 TX Bit 1 Master TX Bit 1 1) DS1921 TX Bit 1 Master TX Bit 1 Bit 1 Match? Y N N Bit 1 Match? Y 1) 1) 1) DS1921 TX Temp. Range Pattern and Serial Number 6 Bytes 1) 1) 1) 1) DS1921 TX CRC Byte 1) Master TX Bit 63 1) DS1921 TX Bit 63 1) DS1921 TX Bit 63 1) Master TX Bit 63 Bit 63 Match? Y N N Bit 63 Match? Y 1) To Figure 12 nd 2 Part 1) 2) To be transmitted or received at Overdrive speed if OD = 1. The Presence Pulse will be short if OD = 1. To Memory Functions Flow Chart (Figure 10) From Figure 12 nd 2 Part 25 of 40 DS1921L ROM FUNCTIONS FLOW CHART Figure 12-2 To Figure 12 st 1 Part From Figure 12 st 1 Part CCH Skip ROM? Y N 3CH Overdrive Skip ROM? Y OD = 1 N 69H Overdrive Match? Y OD = 1 N Master TX Bit 0 3) Bit 0 Match? Y Master TX Bit 1 Y Master TX Reset Pulse? N Bit 1 Match? Y N 3) N Master TX Bit 63 3) From Figure 12 st 1 Part Bit 63 Match? Y N To Figure 12 st 1 Part 3) Always to be transmitted at Overdrive speed. 26 of 40 DS1921L Overdrive Skip ROM [3Ch] On a single-drop bus this command can save time by allowing the bus master to access the memory functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets the DS1921L in the Overdrive mode (OD = 1). All communication following this command has to occur at Overdrive speed until a reset pulse of minimum 480s 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 will speed 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 will occur on the bus as multiple slaves transmit simultaneously (open drain pull-downs 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 DS1921L on a multidrop bus and to simultaneously set it in Overdrive mode. Only the DS1921L that exactly matches the 64-bit ROM sequence will respond to the subsequent memory function command. Slaves already in Overdrive mode from a previous Overdrive Skip or Match command will remain in Overdrive mode. All overdrive-capable slaves will return to standard speed at the next Reset Pulse of minimum 480s duration. The Overdrive Match ROM command can be used with a single or multiple devices on the bus. 1-WIRE SIGNALING The DS1921L 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 0, Write 1, and Read Data. Except for the presence pulse the bus master initiates all these signals. The DS1921L can communicate at two different speeds: standard speed and Overdrive speed. If not explicitly set into the Overdrive mode, the DS1921L will communicate 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 voltage VILMAX is relevant for the DS1921L when determining a logical level, but not for triggering any events. The initialization sequence required to begin any communication with the DS1921L is shown in Figure 13. A Reset Pulse followed by a Presence Pulse indicates the DS1921L is ready to receive data, given the correct ROM and memory function command. In a mixed population network, the reset low time tRSTL needs to be long enough for the slowest 1-Wire slave device to recognize it as a reset pulse. With the DS1921L this duration is 480s at standard speed and 62s at Overdrive speed. 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 480s or longer will exit the Overdrive Mode returning the device to standard speed. If the DS1921L is in Overdrive Mode and tRSTL is no longer than 80s, the device will remain in Overdrive Mode. 27 of 40 DS1921L INITIALIZATION PROCEDURE (RESET AND PRESENCE PULSES) Figure 13 MASTER TX RESET PULSE VPUP VIHMASTER VTH VTL VILMAX 0V MASTER RX PRESENCE PULSE e tMSP tF tRSTL tPDH MASTER tPDL tRSTH tREC DS1921L RESISTOR After the bus master has released the line it goes into receive mode (RX). Now, the 1-Wire bus is pulled to VPUP via the pull-up resistor or, in case of a DS2480B driver, by active circuitry. When the threshold VTH is crossed, the DS1921L 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 DS1921L 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 1Wire devices. Read/Write Time Slots Data communication with the DS1921L takes place in time slots that 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 14. 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 DS1921L starts its internal time base. The tolerance of the slave time base creates a slave-sampling window that stretches from tSLSMIN to tSLSMAX. The voltage on the data line at the sampling point determines whether the DS1921L decodes the time slot as 1 or 0. For reliable communication the voltage has to be either below the VILMAX or above the maximum VTH value during the entire sampling window. Master to Slave For a write-one time slot, the master pull-down time (tMPD1 = tW1L -e + tF) must be short enough to allow the voltage on the 1-Wire line to reach VTH at tSLSMIN, the earliest sampling point of a DS1921L. After the latest sampling point (tSLSMAX)there needs to be a recovery time (tREC) before the next time slot can start. For a write-zero time slot, the master pull-down time (tMPD0 = tW0L + tF) must be long enough to keep the voltage on the data line below VILMAX at the sampling point of a slow DS1921L, which is tSLSMAX. Before the next time slot can start, the voltage on the data line first needs to rise above VTH and remain there until the recovery time tREC is expired. 28 of 40 DS1921L READ/WRITE TIMING DIAGRAM Figure 14 Write-One Time Slot VPUP VIHMASTER VTH VTL VILMAX 0V tF tW1L DS1921L Sampling Window e tSLSMIN tSLSMAX tSLOT RESISTOR MASTER DS1921L tREC Write-Zero Time Slot VPUP VIHMASTER VTH VTL VILMAX 0V tF tSLSMIN tSLSMAX tW0L DS1921L Sampling Window tREC tSLOT DS1921L RESISTOR MASTER Read-Data Time Slot VPUP VIHMASTER VTH VTL VILMAX 0V tF d tRL tMSR Master Sampling Window tREC tSPDMIN tSPDMAX tSLOT RESISTOR MASTER DS1921L Slave to Master A read-data time slot is very similar to a write-one time slot. The master begins a read-data time slot with pulling the data line low. As the voltage on the 1-Wire line falls below the threshold VTL, the DS1921L starts its internal time base. The master pull-down time (tMPDR = tRL + tF) must be long enough to cover the setup time tSU, after which the DS1921L delivers a bit to its 1-Wire port. When transmitting a 0, the DS1921L will hold the data line low for tSPD. If the data bit is a 1, the DS1921L will not hold the data line low at all. 29 of 40 DS1921L The master samples the data line at tMSR, inside a window that is determined by the sum of tRL and the rise time (d) on one side and tSPDMIN on the other side. The optimum sample point for a read-zero case is no later than tSPDMIN. In case of a read-one, the voltage on the 1-Wire line must be able to reach VIHMASTER at tMSR. This condition determines the maximum duration of the master pull-down time. For reliable communication, the master pull-down time should be as short as possible, maximizing the time for the data line to reach VIHMIN. Before the next time slot can start, tSPDMAX needs to be over and the voltage on the data line must have risen above VTH and remained there until the recovery time tREC is expired. CRC GENERATION With the DS1921L there are two different types of Cyclic Redundancy Checks (CRCs). One CRC is an 8bit 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 DS1921L to determine if the ROM data has been received error-free. The equivalent polynomial function of this CRC is X8 + X5 + X4 + 1. This 8-bit CRC is received in the true (non-inverted) 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 X16 + X15 + X2 + 1. This CRC is used for error detection when reading data memory using the Read Memory with CRC command and for fast verification of a data transfer when writing to or reading from the scratchpad. It is the same type of CRC as is used with NV RAM-based iButtons for error detection within the iButton Extended File Structure. In contrast to the 8-bit CRC, the 16-bit CRC is always communicated in the inverted form. A CRC-generator inside the DS1921L chip (Figure 15) will calculate a new 16-bit CRC as shown in the command flow chart of Figure 10. 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. Subsequent passes through the Read Memory with CRC flow chart will 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 DS1921L will transmit this CRC only if the data bytes written to the scratchpad include scratchpad ending offset 11111b. The data may 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 DS1921L will transmit 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 Application Note 27 or the Book of DS19xx iButton Standards. 30 of 40 DS1921L CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL Figure 15 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 31 of 40 DS1921L MISSION EXAMPLE: PREPARE AND START A NEW MISSION Assumption: The previous mission has come to an end. To end an ongoing mission one may, for example, perform a sequence as in step 1 or write the MIP bit in the Status Register to 0. The preparation of a DS1921L for a mission including the start of the mission requires up to four steps: Step 1: set the RTC (if it needs to be adjusted) Step 2: clear the data of the previous mission Step 3: set the search condition and mission start delay Step 4: set the temperature alarms and write the sample rate to start the mission Let the actual time be 15:30:00 hours on Monday, the 1st of April in 2002. This results in the following data to be written to the RTC registers: Address: Data: 200h 00h 201h 30h 202h 15h 203h 01h 204h 81h 205h 04h 206h 02h STEP 1 With only a single DS1921L connected to the bus master, the communication of step 1 is as follows: MASTER MODE TX RX TX TX TX TX TX TX RX TX TX RX RX RX RX TX RX TX TX TX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 0Fh 00h 02h <7 data bytes> (Reset) (Presence) CCh AAh 00h 02h 06h <7 data bytes> (Reset) (Presence) CCh 55h 00h 02h 06h (Reset) (Presence) COMMENTS Reset pulse (480s to 960s) Presence pulse Issue Skip ROM command Issue Write Scratchpad command TA1, beginning offset = 00h TA2, address = 0200h Write 7 bytes of data to 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 = 6h, 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 Reset pulse Presence pulse 32 of 40 DS1921L STEP 2 Set the EMCLR bit to 1, enable the RTC and then execute the Clear Memory command. This results in the following data to be written to the Status Register: Address: Data: 20Eh 40h With only a single DS1921L connected to the bus master, the communication of step 2 is as follows: MASTER MODE TX RX TX TX TX TX TX TX RX TX TX RX RX RX RX TX RX TX TX TX TX TX TX RX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 0Fh 0Eh 02h 40h (Reset) (Presence) CCh AAh 0Eh 02h 0Eh 40h (Reset) (Presence) CCh 55h 0Eh 02h 0Eh (Reset) (Presence) CCh 3Ch (Reset) (Presence) COMMENTS Reset pulse (480s to 960s) Presence pulse Issue Skip ROM command Issue Write Scratchpad command TA1, beginning offset = 0Eh TA2, address = 020Eh Write status byte to scratchpad Reset pulse Presence pulse Issue Skip ROM command Issue Read Scratchpad command Read TA1, beginning offset = 0Eh Read TA2, address = 020Eh Read E/S, ending offset = 0Eh, 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 Reset pulse Presence pulse Issue Skip ROM command Issue Clear Memory command Reset pulse Presence pulse 33 of 40 DS1921L STEP 3 In this example, the rollover is disabled and the search condition is set for a high temperature only. The mission is to start with a delay of 90 (5Ah) minutes. This results in the following data to be written to the special function registers: Address: Data: 20Eh 02h 20Fh 00h* 210h 00h* 211h 00h* 212h 5Ah 213h 00h * Writing through address locations 20Fh to 211h is faster than accessing the Mission Start Delay Register in a separate cycle. The write attempt has no effect on the contents of these registers. With only a single DS1921L connected to the bus master, the communication of step 3 is as follows: MASTER MODE TX RX TX TX TX TX TX TX RX TX TX RX RX RX RX TX RX TX TX TX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 0Fh 0Eh 02h <6 data bytes> (Reset) (Presence) CCh AAh 0Eh 02h 13h <6 data bytes> (Reset) (Presence) CCh 55h 0Eh 02h 13h (Reset) (Presence) COMMENTS Reset Pulse (480s to 960s) Presence pulse Issue Skip ROM command Issue Write Scratchpad command TA1, beginning offset = 0Eh TA2, address = 020Eh Write 6 bytes of data to scratchpad Reset pulse Presence pulse Issue Skip ROM command Issue Read Scratchpad command Read TA1, beginning offset = 0Eh Read TA2, address = 020Eh Read E/S, ending offset = 13h, 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 Reset pulse Presence pulse 34 of 40 DS1921L STEP 4 In this example, the temperature alarms are set to -5C for the low temperature threshold and 0C for the high temperature threshold. The sample rate is once every 10 minutes, allowing the mission to last up to 14 days. This results in the following data to be written to the special function registers: Address: Data: 20Bh 46h 20Ch 50h 20Dh 0Ah With only a single DS1921L connected to the bus master, the communication of step 4 is as follows: MASTER MODE TX RX TX TX TX TX TX TX RX TX TX RX RX RX RX TX RX TX TX TX TX TX TX RX DATA (LSB FIRST) (Reset) (Presence) CCh 0Fh 0Bh 02h <3 data bytes> (Reset) (Presence) CCh AAh 0Bh 02h 0Dh <3 data bytes> (Reset) (Presence) CCh 55h 0Bh 02h 0Dh (Reset) (Presence) COMMENTS Reset pulse (480s to 960s) Presence pulse Issue Skip ROM command Issue Write Scratchpad command TA1, beginning offset = 0Bh TA2, address = 020Bh Write 3 bytes of data to scratchpad Reset pulse Presence pulse Issue Skip ROM command Issue Read Scratchpad command Read TA1, beginning offset = 0Bh Read TA2, address = 020Bh Read E/S, ending offset = 0Dh, 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 Reset pulse Presence pulse If step 4 was successful, the Mission Time Stamp Register will contain the date and time of the RTC, the MIP bit in the Status Register will be 1 and the MEMCLR bit will be 0. 35 of 40 DS1921L PHYSICAL SPECIFICATION Size Weight Humidity Altitude Safety See mechanical drawing 3.3g 90% RH at 50C 10,000ft Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus, approval under Entity Concept for use in Class I, Division 1, Group A, B, C and D Locations (application pending) ABSOLUTE MAXIMUM RATINGS* IO Voltage to GND IO sink current Temperature Range Junction Temperature Storage Temperature Range * -0.5V, +6V 20mA -40C to +85C +150C -25C to +50C 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. These devices must not be exposed to temperatures over 70C for extended time periods. ELECTRICAL CHARACTERISTICS (VPUP = 2.8V to 5.25V, TA = -40C to +85C) MIN TYP MAX UNITS NOTES 2.2 100 1.14 0.71 1.00 0.66 5 2 5 65 8 s 1, 15 800 10 2.70 2.70 0.30 2.70 2.70 0.4 kW pF A V V V V s 1, 2 3, 16 4 5, 6, 7, 16 1, 5, 8 5, 6, 9, 16 5, 10 1, 16 PARAMETER SYMBOL CONDITIONS IO pin general data 1-Wire Pull-up RPUP Resistance Input Capacitance CIO Input Load Current IL IO pin at VPUP High-to-Low VTL VPUP > 4.5V Switching Threshold Input Low Voltage VIL Low-to-High VTH VPUP > 4.5V Switching Threshold Output low voltage at VOL 4mA Recovery Time tREC Standard Speed, RPUP = 2.2kW Overdrive Speed, RPUP = 2.2kW Overdrive Speed, directly prior to reset pulse; RPUP = 2.2kW Timeslot Duration tSLOT Standard Speed Overdrive Speed 36 of 40 DS1921L PARAMETER SYMBOL CONDITIONS IO pin, 1-Wire Reset, Presence detect cycle Reset Low Time tRSTL Standard Speed, VPUP > 4.5V Standard Speed Overdrive Speed Presence Detect High tPDH Standard Speed Time Overdrive Speed Presence Detect Low tPDL Standard Speed Time Overdrive Speed Presence Detect tMSP Standard Speed Sample Time Overdrive Speed IO pin, 1-Wire Write Write-0 Low Time tW0L Standard Speed Overdrive Speed Write-1 Low Time tW1L Standard Speed Overdrive Speed Write Sample Time tSLS Standard Speed (slave sampling) Overdrive Speed IO pin, 1-Wire Read Read Low Time tRL Standard Speed Overdrive Speed Read-0 Low tSPD Standard Speed (data from slave) Overdrive Speed Read Sample Time tMSR Standard Speed Overdrive Speed Real Time Clock Frequency Deviation -5C to +46C DF Temperature Converter Tempcore Operating TTC DS1921L-F50 Range DS1921L-F51 DS1921L-F52 DS1921L-F53 Conversion Time tCONV Thermal Response tRESP Time Constant Conversion Error DJ Number of NCONV Conversions MIN 480 540 48 15 1.1 60 7.5 60 6 60 6 5 1 15 2 5 1 15 2 tRL + d tRL + d -48 -40 -10 -20 -30 19 TYP MAX UNITS NOTES 640 640 80 60 6 270 24 75 8.6 120 15 15 - e 2-e 60 6 15 - d 2-d 60 6 15 2 +46 +85 +85 +85 +85 90 s 1, 15 s s s s s s s s s 15 15 1, 16 1, 15 1, 11 15 1, 12 15 1, 12 PPM C 130 -1 (see graphs) +1 ms s C --- 13, 16 14, 16 37 of 40 DS1921L NOTES 1) System Requirement. 2) Maximum allowable pull-up 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 pull-up such as that found in the DS2480 may be required. 3) Capacitance on the data pin could be 800pF when power is first applied. If a 5kW resistor is used to pull up the data line to VPUP; the parasite capacitance will not affect normal communications 5s after power has been applied. 4) Input load is to ground. 5) All voltages are referenced to ground. 6) VTL, VTH are a function of the internal supply voltage. 7) Voltage below which, during a falling edge on IO, a logic 0 is detected. 8) The voltage on IO needs to be less or equal to VILMAX whenever the master drives the line low. 9) Voltage above which, during a rising edge on IO, a logic 1 is detected. 10) The I-V characteristic is linear for voltages less than 1V. 11) e represents the time required for the pull-up circuitry to pull the voltage on IO up from VIL to VTH. 12) d represents the time required for the pull-up circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus master. 13) 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 14) The number of temperature conversions (= Samples) possible with the built-in energy source depends on the operating and storage temperature of the device. When not in use for a mission, the RTC oscillator should be turned off and device should be stored at a temperature not exceeding 25C. Under this condition the shelf life time is 10 years minimum. 15) Highlighted numbers are not in compliance with the published iButton standards. See comparison table below. 16) These values are derived from simulation across process, voltage, and temperature and are not production tested. Parameter Name tSLOT (incl. tREC) tRSTL tPDH tPDL tW0L tSLS, tSPD Standard Standard Speed min max 61s (undef.) 480s (undef.) 15s 60s 60s 240s 60s 120s 15s 60s Values Overdrive Speed min max 7s (undef.) 48s 80s 2s 6s 8s 24s 6s 16s 2s 6s DS1921L Standard Speed min max 65s (undef.) 540s 640s 15s 60s 60s 270s 60s 120s 15s 60s Values Overdrive Speed min max 8s (undef.) 48s 80s 1.1s 6s 7.5s 24s 6s 15s 2s 6s 38 of 40 DS1921L RTC Frequency Deviation vs Temperature Lower Limit 50 Upper Limit Frequency Deviation (PPM) 25 0 -25 -50 -75 -100 -125 -150 -175 -200 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 Temperature (C) Minimum Product Lifetime vs Temperature at Different Sample Rates Every Minute No Samples 11.00 Every 3 Min. Osc. Off Every 10 Min. Min. Product Lifetime (years) 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 Temperature (C) 39 of 40 DS1921L Minimum Product Lifetime vs Sample Rate at Different Temperatures -40C 50C 11.00 -20 C 55C 15C 60C 40C 70C 45C 85C Minimum Product Lifetime (years) 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 1 10 100 1000 Minutes between Samples 40 of 40 |
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