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ICM7170
August 1997
Microprocessor-Compatible, Real-Time Clock
Description
The ICM7170 real time clock is a microprocessor bus compatible peripheral, fabricated using Intersil's silicon gate CMOS LSl process. An 8-bit bidirectional bus is used for the data I/O circuitry. The clock is set or read by accessing the 8 internal separately addressable and programmable counters from 1/100 seconds to years. The counters are controlled by a pulse train divided down from a crystal oscillator circuit, and the frequency of the crystal is selectable with the onchip command register. An extremely stable oscillator frequency is achieved through the use of an on-chip regulated power supply. The device access time (tACC) of 300ns eliminates the need for wait states or software overhead with most microprocessors. Furthermore, an ALE (Address Latch Enable) input is provided for interfacing to microprocessors with a multiplexed address/data bus. With these two special features, the ICM7170 can be easily interfaced to any available microprocessor. The ICM7170 generates two types of interrupts, periodic and alarm. The periodic interrupt (100Hz, 10Hz, etc.) can be programmed by the internal interrupt control register to provide 6 different output signals. The alarm interrupt is set by loading an on-chip 51-bit RAM that activates an interrupt output through a comparator. The alarm interrupt occurs when the real time counter and alarm RAM time are equal. A status register is available to indicate the interrupt source. An on-chip Power Down Detector eliminates the need for external components to support the battery back-up function. When a power down or power failure occurs, internal logic switches the on-chip counters to battery backup operation. Read/write functions become disabled and operation is limited to time-keeping and interrupt generation, resulting in low power consumption. Internal latches prevent clock roll-over during a read cycle. Counter data is latched on the chip by reading the 100th-seconds counter and is held indefinitely until the counter is read again, assuring a stable and reliable time value.
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Features
* 8-Bit, P Bus Compatible - Multiplexed or Direct Addressing * Regulated Oscillator Supply Ensures Frequency Stability and Low Power * Time From 1/100 Seconds to 99 Years * Software Selectable 12/24 Hour Format * Latched Time Data Ensures No Roll Over During Read * Full Calendar with Automatic Leap Year Correction * On-Chip Battery Backup Switchover Circuit * Access Time Less than 300ns * 4 Programmable Crystal Oscillator Frequencies Over Industrial Temperature Range * 3 Programmable Crystal Oscillator Frequencies Over Military Temperature Range * On-Chip Alarm Comparator and RAM * Interrupts from Alarm and 6 Selectable Periodic Intervals * Standby Micro-Power Operation: 1.2A Typical at 3.0V and 32kHz Crystal
Applications
* Portable and Personal Computers * Data Logging * Industrial Control Systems * Point Of Sale
Ordering Information
PART NUMBER ICM7170IPG ICM7170IDG ICM7170IBG ICM7170MDG ICM7170AIPG ICM7170AIDG ICM7170AIBG ICM7170AMDG NOTE: TEMP. RANGE (oC) -40 to 85 -40 to 85 -40 to 85 -55 to 125 -40 to 85 -40 to 85 -40 to 85 -55 to 125 PACKAGE 24 Ld PDIP 24 Ld SBDIP 24 Ld SOIC 24 Ld SBDIP 24 Ld PDIP 24 Ld SBDIP 24 Ld SOIC 24 Ld SBDIP PKG. NO. E24.6 D24.6 M24.3 D24.6 E24.6 D24.6 M24.3 D24.6
"A" Parts Screened to <5A ISTBY at 32kHz.
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. http://www.intersil.com or 407-727-9207 | Copyright (c) Intersil Corporation 1999
File Number
3019.3
12-5
ICM7170 Pinouts
ICM7170 (PDIP, SBDIP) TOP VIEW
WR 1 ALE 2 CS 3 A4 4 A3 5 A2 6 A1 7 A0 8 OSC OUT 9 OSC IN 10 INT SOURCE 11 INTERRUPT 12 24 RD 23 VDD 22 D7 21 D6 20 D5 19 D4 18 D3 17 D2 16 D1 15 D0 14 VBACKUP 13 VSS (GND)
ICM7170 (SOIC) TOP VIEW
A1 1 A0 2 OSC OUT 3 OSC IN 4 INT SOURCE 5 INT 6 VSS 7 VBACKUP 8 D0 9 D1 10 D2 11 D3 12 24 A2 23 A3 22 A4 21 CS 20 ALE 19 WR 18 RD 17 VDD 16 D7 15 D6 14 D5 13 D4
Functional Block Diagram
OSCILLATOR CRYSTAL OSC OUT 9 OSC IN 10 INTERRUPTS RD WR ALE CS 24 1 2 3 P CONTROL INT 11 SOURCE YEAR LOW POWER OSC PERIODIC COMPARE 12 INT
TIME COUNTERS 0.01 VDD VBACKUP VSS 23 14 13 POWER SUPPLY CONTROL 8 SEC MIN HOUR DAY DATE MON
8-BIT BUS
THREE-STATE I/O DRIVERS
8 15 - 22
DATA I/O D0 - D7
8 ADDRESS INPUTS A0 - A4
5 8-4
ADDRESS LATCHES
0.01
SEC
MIN
HOUR DAY
DATE MON
YEAR
COMPARE RAM
CMD REG
STATUS REG
INTER MASK REG
12-6
ICM7170
Absolute Maximum Ratings
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +8.0V Power Dissipation (Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . 500mW Storage Temperature Range . . . . . . . . . . . . . . . . . . -65oC to 150oC Lead Temperature (Soldering 10s) . . . . . . . . . . . . . . . . . . . . . 300oC Input Voltage (Any Terminal) (Note 2) . . . . VDD +0.3V to VSS -0.3V
Thermal Information
Thermal Resistance (Typical, Note 3) JA (oC/W) JC (oC/W) PDIP Package . . . . . . . . . . . . . . . . . . . 65 N/A SBDIP Package . . . . . . . . . . . . . . . . . . 60 18 SOIC Package . . . . . . . . . . . . . . . . . . . 75 N/A Maximum Junction Temperature Plastic Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150oC SBDIP Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175oC
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES: 1. TA = 25oC. 2. Due to the SCR structure inherent in the CMOS process, connecting any terminal at voltages greater than VDD or less than VSS may cause destructive device latchup. For this reason, it is recommended that no inputs from external sources not operating on the same power supply be applied to the device before its supply is established, and that in multiple supply systems, the supply to the ICM7170 be turned on first. 3. JA is measured with the component mounted on an evaluation PC board in free air.
DC Electrical Specifications
PARAMETER VDD Supply Range, VDD
TA = -40oC to 85oC, VDD +5V 10%, VBACKUP VDD , VSS = 0V Unless Otherwise Specified All IDD specifications include all input and output leakages (ICM7170 and ICM7170A) TEST CONDITIONS fOSC = 32kHz fOSC = 1, 2, 4MHz MIN 1.9 2.6 ICM7170 ICM7170A TYP 1.2 1.2 MAX 5.5 5.5 20.0 5.0 UNITS V V A A
Standby Current, ISTBY(1)
fOSC = 32kHz Pins 1 - 8,15 - 22 and 24 = VDD VDD = VSS ; VBACKUP = VDD - 3.0V For ICM7170A See General Notes 5
Standby Current, ISTBY(2)
fOSC = 4MHz Pins 1 - 8,15 - 22 and 24 = VDD VDD = VSS ; VBACKUP = VDD - 3.0V fOSC = 32kHz Read/Write Operation at 100Hz fOSC = 32kHz Read/Write Operation at 1MHz VDD = 5.0V VDD = 5.0V IOL = 1.6mA IOH = -400A
-
20
150
A
Operating Supply Current, IDD(1) Operating Supply Current, IDD(2) Input Low Voltage (Except Osc.), VIL Input High Voltage (Except Osc.), VIH Output Low Voltage (Except Osc.), VOL Output High Voltage Except INTERRUPT (Except Osc.), VOH Input Leakage Current, IIL Three-State Leakage Current (D0 - D7), IOL(1) Backup Battery Voltage, VBATTERY Backup Battery Voltage, VBATTERY
2.4 2.4
0.3 1.0 -
1.2 2.0 0.8 0.4 -
mA mA V V V V
VIN = VDD or VSS VO = VDD or VSS fOSC = 1, 2, 4MHz fOSC = 32kHz
-10 -10 2.6 1.9
0.5 0.5 -
+10 +10 VDD - 1.3 VDD - 1.3
A A V V
12-7
ICM7170
DC Electrical Specifications
PARAMETER Leakage Current INTERRUPT, IOL(2) Capacitance D0 - D7, CI/O Capacitance A0 - A4, CADDRESS VO = VDD TA = -40oC to 85oC, VDD +5V 10%, VBACKUP VDD , VSS = 0V Unless Otherwise Specified All IDD specifications include all input and output leakages (ICM7170 and ICM7170A) (ContinTEST CONDITIONS INT SOURCE Connected to VSS MIN TYP 0.5 8 6 MAX 10 UNITS A pF pF
AC Electrical Specifications
TA = -40oC to 85oC, VDD = +5V 10%, VBACKUP = VDD , D0 - D7 Load Capacitance = 150pF, VIL = 0.4V, VlH = 2.8V, Unless Otherwise Specified MIN MAX UNITS
PARAMETER READ CYCLE TIMING READ to DATA Valid, tRD ADDRESS Valid to DATA Valid, tACC READ Cycle Time, tCYC Read High Time, tRH RD High to Bus Three-State, tRH ADDRESS to READ Set Up Time, tAS ADDRESS HOLD Time After READ, tAR WRITE CYCLE TIMING ADDRESS Valid to WRITE Strobe, tAD ADDRESS Hold Time for WRITE, tWA WRITE Pulse Width, Low, tWL WRITE High Time, tWH DATA IN to WRITE Set Up Time, tDW DATA IN Hold Time After WRITE, tWD WRITE Cycle Time, tCYC MULTIPLEXED MODE TIMING ALE Pulse Width, High, tLL ADDRESS to ALE Set Up Time, tAL ADDRESS Hold Time After ALE, tLA
400 150 50 0
250 300 25 -
ns ns ns ns ns ns ns
50 0 100 300 100 30 400
-
ns ns ns ns ns ns ns
50 30 30
-
ns ns ns
12-8
ICM7170 Timing Diagrams
A0 - A4, CS tAS tCYC RD tRD ADDRESS VALID, CS LOW tAR
D0 - D7 tACC
OUTPUT DATA VALID tRX
FIGURE 1. READ CYCLE TIMING FOR NON-MULTIPLEXED BUS (ALE = VIH , WR = VIH)
A0 - A4, CS tAD
ADDRESS VALID, CS LOW tWA tCYC tWL
WR
tDW
tWD
D0 - D7
INPUT DATA VALID
FIGURE 2. WRITE CYCLE TIMING FOR NON-MULTIPLEXED BUS (ALE = VIH , RD = VIH)
A0 - A4, D0 - D7, CS
ADDRESS VALID, CS LOW
OUTPUT DATA VALID
tLA tLL tACC ALE tAR
tAL
tCYC
RD
tAS tRD
FIGURE 3. READ CYCLE TIMING FOR MULTIPLEXED BUS (WR = VIH)
12-9
ICM7170 Timing Diagrams
A0 - A4, D0 - D7, CS
(Continued)
ADDRESS VALID, CS LOW tLA tLL
INPUT DATA VALID tDW tWD tWA
ALE tAL tAD WR tWL tCYC
FIGURE 4. WRITE CYCLE TIMING FOR MULTIPLEXED BUS (RD = VIH)
Pin Descriptions
SIGNAL WR ALE CS A4-A0 OSC OUT OSC IN INT SOURCE INTERRUPT VSS (GND) VBACKUP D0 - D7 VDD RD PIN NUMBER 1 2 3 4-8 9 10 11 12 13 14 15 - 22 23 24 SOIC PIN NUMBER 19 20 21 22 - 2 3 4 5 6 7 8 9 - 16 17 18 Write Input Address Latch Enable Input Chip Select Input Address Inputs Oscillator Output Oscillator Input Interrupt Source Interrupt Output Digital Common Battery Negative Side Data I/O Positive Digital Supply Read Input DESCRIPTION
TABLE 1. COMMAND REGISTER FORMAT COMMAND REGISTER ADDRESS (10001b, 11h) WRITE-ONLY D7 n/a D6 n/a D5 Normal/Test Mode D4 Interrupt Enable D3 Run/Stop D2 12/24 Hour Format D1 Crystal Frequency D0 Crystal Frequency
TABLE 2. COMMAND REGISTER BIT ASSIGNMENTS INTERRUPT ENABLE Interrupt disabled Interrupt enable 24/12 HOUR FORMAT 12-Hour Mode 24-Hour Mode CRYSTAL FREQUENCY 32.768kHz 1.048576MHZ 2.097152MHz 4.194304MHz
D5 0 1
TEST BIT Normal Mode Test Mode
D4 0 1
D3 0 1
RUN/STOP Stop Run
D2 0 1
D1 0 0 1 1
D0 0 1 0 1
12-10
ICM7170
TABLE 3. ADDRESS CODES AND FUNCTIONS ADDRESS A4 0 0 A3 0 0 A2 0 0 Al 0 0 A0 0 1 HEX 00 01 FUNCTION Counter-1/100 seconds Counter-hours 12 Hour Mode 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 0 1 02 03 04 05 06 07 08 09 Counter-minutes Counter-seconds Counter-month Counter-date Counter-year Counter-day of week RAM-1/100 seconds RAM-hours 12 Hour Mode 0 0 0 0 0 0 1 1 NOTES: Addresses 10010 to 11111 (12h to 1Fh) are unused. `+' Unused bit for interrupt Mask Register, MSB bit for interrupt Status Register. `-' Indicates unused bits. `' AM/PM indicator bit in 12 hour format Logic "0" indicates AM, logic "1" indicates PM. `M' Alarm compare for particular counter will be enabled if bit is set to logic "0". 1 1 1 1 1 1 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 1 0 1 0A 0B 0C 0D 0E 0F 10 11 RAM-minutes RAM-seconds RAM-month RAM-date RAM-year RAM-day of week Interrupt Status and Mask Register Command register D7 D6 D5 DATA D4 D3 D2 D1 D0 VALUE 0 - 99 0 - 23 1 - 12 0 - 59 0 - 59 1 - 12 1 - 31 0 - 99 0-6 0 - 99 M M . . . . 0 - 23 1 - 12 0 - 59 0 - 59 1 - 12 1 - 31 0 - 99 0-6
M -
M M M M M M + -
-
TABLE 4. INTERRUPT AND STATUS REGISTERS FORMAT INTERRUPT MASK REGISTER ADDRESS (10000b, 10h) WRITE-ONLY D7 NOT USED D6 DAY D5 HOUR D4 MIN D3 SEC D2 1/10 SEC D1 1/100 SEC D0 ALARM Alarm/Compare Mask Bit
Periodic Interrupt Mask Bits
INTERRUPT STATUS REGISTER ADDRESS (10000b, 10h) READ-ONLY D7 GLOBAL INTERRUPT Periodic and Alarm Flags D6 DAY D5 HOUR D4 MIN D3 SEC D2 1/10 SEC D1 1/100 SEC D0 ALARM Alarm Compare Flag
Periodic Interrupt Flags
12-11
ICM7170 Detailed Description
Oscillator The ICM7170 has an onboard CMOS Pierce oscillator with an internally regulated voltage supply for maximum accuracy, stability, and low power consumption. It operates at any of four popular crystal frequencies: 32.768kHz, 1.046576MHz, 2.097152MHz, and 4.194304MHz (Note 1). The crystal should be designed for the parallel resonant mode of oscillation. In addition to the crystal, 2 or 3 load capacitors are required, depending on the circuit topology used. The oscillator output is divided down to 4000Hz by one of four divider ratios, determined by the two frequency selection bits in the Command Register (D0 and D1 at address 11H). This 4000Hz is then divided down to 100Hz, which is used as the clock for the counters. Time and calendar information is provided by 8 consecutive, programmable counters: 100ths of, seconds, minutes, hours, day of week, date, month, and year. The data is in binary format with 8 bits per digit. See Table 3 for address information. Any unused bits are held to a logic "0" during a read and ignored during a write operation.
NOTE: 1. 4.94304MHz is not available over military temperature range.
Periodic Interrupts The interrupt output can be programmed for 6 periodic signals: 100Hz, 10Hz, once per second, once per minute, once per hour, or once per day. The 100Hz and 10Hz interrupts have instantaneous errors of 2.5% and 0.15% respectively. This is because non-integer divider circuitry is used to generate these signals from the crystal frequency, which is a power of 2. The time average of these errors over a 1 second period, however, is zero. Consequently, the 100Hz or 10Hz interrupts are not suitable as an aid in tuning the oscillator; the 1 second interrupt must be used instead. See General Notes, Note 6. The periodic interrupts can occur concurrently and in addition to alarm interrupts. The periodic interrupts are controlled by bits in the interrupt mask register, and are enabled by setting the appropriate bit to a "1" as shown in Table 4. Bits D1 through D6 in the mask register, in conjunction with bits D1 through D6 of the status register, control the generation of interrupts according to Figure 5. The interrupt status register, when read, indicates the cause of the interrupt and resets itself on the rising edge of the RD signal. When any of the counters having a corresponding bit in the status register increments, that bit is set to a "1" regardless of whether the corresponding bit in the interrupt mask register is set or not. Consequently, when the status register is read it will always indicate which counters have increments and if an alarm compare occurred, since the last time it was read. This requires some special software considerations. If a slow interrupt is enabled (i.e. hourly or daily), the program must always check the slowest interrupt that has been enabled first, because all the other lower order bits in the status register will be set to "1" as well. Bit D7 is the global interrupt bit, and when set to a "1", indicates that the ICM7170 did indeed generate a hardware interrupt. This is useful when other interrupting devices in addition to the ICM7170 are attached to the system microprocessor, and all devices must be polled to determine which one generated the interrupt. See General Notes, Note 6.
Alarm Compare RAM On the chip are 51 bits of Alarm Compare RAM grouped into words of different lengths. These are used to store the time, ranging from 10ths of seconds to years, for comparison to the real-time counters. Each counter has a corresponding RAM word. In the Alarm Mode an interrupt is generated when the current time is equal to the alarm time. The RAM contents are compared to the counters on a word by word basis. If a comparison to a particular counter is unnecessary, then the appropriate `M' bit in Compare RAM should be set to logic "1". The `M' bit, referring to Mask bit, causes a particular RAM word to be masked off or ignored during a compare. Table 3 shows addresses and Mask bit information.
12-12
ICM7170
PERIODIC INT' MASK BITS INTERRUPT MASK REGISTER D7 D6 D5 D4 D3 D2 D1 D0 ALARM MASK BIT
NOT USED
PIN 12 INT
VIG INT SOURCE PIN 11
INTERRUPT STATUS REGISTER
D7
D6
D5
D4
D3
D2
D1
D0
RD OF ADD HEX 10 = >RESET
PERIODIC INT' FLAGS GLOBAL INTERRUPT FLAG BIT
ALARM FLAG BIT
INTERRUPT ENABLE COMMAND REGISTER BIT D4
FIGURE 5. INTERRUPT OUTPUT CIRCUIT
Interrupt Operation The Interrupt Output N-channel MOSFET (Figure 4) is enabled whenever both the Interrupt Enable bit (D4 of the Command Register) and a mask bit (D0 - D6 of the Interrupt Mask Register) are set. The transistor is turned ON when a flag bit is set that corresponds to one of the set mask bits. This also sets the Global Interrupt Flag Bit (D7 of the Interrupt Status Register). It is turned OFF when the Interrupt Status Register is read. An interrupt can occur in both the operational and standby modes of operation. Since system power is usually applied between VDD and VSS , the user can connect the Interrupt Source (pin 11) to VSS . This allows the Interrupt Output to turn on only while system powers applied and will not be pulled to VSS during standby operation. If interrupts are required only during standby operation, then the interrupt source pin should be connected to the battery's negative side (VBACKUP). In this configuration, for example, the interrupt could be used to turn on power for a cold boot. Power Down Detector The ICM7170 contains an on-chip power down detector that eliminates the need for external components to support the battery-backup switchover function, as shown in Figure 6. Whenever the voltage from the VSS pin to the VBACKUP pin is less than approximately 1.0V (the VTH of the N-channel MOSFET), the data bus I/O buffers in the ICM7170 are automatically disabled and the chip cannot be read or written to. This prevents random data from the microprocessor being written to the clock registers as the power supply is going down. Actual switchover to battery operation occurs when the voltage on the VBACKUP pin is within 50mV of VSS . This switchover uncertainty is due to the offset voltage of the CMOS comparator that is used to sense the battery voltage. During
battery backup, device operation is limited to timekeeping and interrupt generation only, thus achieving micro- power current drain. If an external battery-backup switch-over circuit is being used with the ICM7170, or if standby battery operation is not required, the VBACKUP pin should be pulled up to VDD through a 2K resistor. Time Synchronization Time synchronization is achieved through bit D3 of the Command Register, which is used to enable or disable the 100Hz clock from the counters. A logic "1" allows the counters to function and a logic "0" disables the counters. To accurately set the time, a logic "0" should be written into D3 and then the desired times entered into the appropriate counters. The clock is then started at the proper time by writing a logic "1" into D3 of the Command Register. Latched Data To prevent ambiguity while the processor is gathering data from the registers, the ICM7170 incorporates data latches and a transparent transition delay circuit. By accessing the 100ths of seconds counter an internal store signal is generated and data from all the counters is transferred into a 36-bit latch. A transition delay circuit will delay a 100Hz transition during a READ cycle. The data stored by the latches is then available for further processing until the 100ths of seconds counter is read again. If a RD signal is wider than 0.01s, 100Hz counts will be ignored. Control Lines The RD, WR, and CS signals are active low inputs. Data is placed on the bus from counters or registers when RD is a logic "0". Data is transferred to counters or registers when WR is a logic "0". RD and WR must be accompanied by a
12-13
ICM7170
POSITIVE SUPPLY RAIL (+5V)
VDD BATTERY PIN 23 VTH R2 2K VBACK PIN 14 VDD + CMOS COMPARATOR
VDD
1.0V
I/O DISABLE
VIG INTERNAL GROUND
VIG VSS PIN 13 DIGITAL GROUND
FIGURE 6. SIMPLIFIED ICM7170 BATTERY BACKUP CIRCUIT
logical "0" CS as shown in Figures 2 and 3. The ICM7170 will also work satisfactorily with CS grounded. In this mode, access to the ICM7170 is controlled by RD and WR only. With the ALE (Address Latch Enable) input, the ICM7170 can be interfaced directly to microprocessors that use a multiplexed address/data bus by connecting the address lines A0 - A4 to the data lines D0 - D4. To address the chip, the address is placed on the bus and ALE is strobed. On the falling edge, the address and CS information is read into the address latch and buffer. RD and WR are used in the same way as on a non-multiplexed bus. If a non-multiplexed bus is used, ALE should be connected to VDD . Test Mode The test mode is entered by setting D5 of the Command Register to a logic "1". This connects the 100Hz counter directly to the oscillator's output. Oscillator Considerations Load Design: A new oscillator load configuration, shown in Figure 7, has been found that eliminates start-up problems sometimes encountered with 32kHz tuning fork crystals.
VDD C1
VDD
C2
X1 OSC IN 10 OSC OUT 9 VDD ICM7170 23
C2 5pF - 35pF
C1 2 x LOAD
FIGURE 8. ORIGINAL OSCILLATOR CONFIGURATION
Two conditions must be met for best oscillator performance: the capacitive load must be matched to both the inverter and crystal to provide the ideal conditions for oscillation, and the resonant frequency of the oscillator must be adjustable to the desired frequency. In the original design (Figure 8), these two goals were often at odds with each other; either the oscillator was trimmed to frequency by detuning the load circuit, or stability was increased at the expense of absolute frequency accuracy. The new load configuration (Figure 6) allows these two conditions to be met independently. The two load capacitors, C1 and C2, provide a fixed load to the oscillator and crystal. C3 adjusts the frequency that the circuit resonates at by reducing the effective value of the crystal's motional capacitance, C0. This minute adjustment does not appreciably change the load of the overall system, therefore, stability is no longer affected by tuning. Typical values for these capacitors are shown in Table 5. C1 and C2 must always be greater than twice the crystal's recommended load capacitance in order for C3 to be able to trim the frequency. Some experimentation may be necessary to determine the ideal values of C1 and C2 for a particular crystal.
C1
C2
X1 OSC IN 10
C3 OSC OUT 9 VDD 23
ICM7170
FIGURE 7. NEW OSCILLATOR CONFIGURATION
12-14
ICM7170
TABLE 5. TYPICAL LOAD CAPACITOR VALUES CRYSTAL FREQUENCY 32kHz 1MHz 2MHz 4MHz LOAD CAPS (C1, C2) 33pF 33pF 25pF 22pF TRIMMER CAP (C3) 5 - 50pF 5 - 50pF 5 - 50pF 5 - 100pF Register several times each second will accomplish this also. 5. Connect a precision period counter capable of measuring 1s within the accuracy desired to the interrupt output. If the interrupt is configured as active low, trigger on the falling edge. If the interrupt is active high, trigger on the rising edge. Be sure to measure the period between when the transistor turns ON, and when the transistor turns ON a second later. 6. Adjust C3 (C2 for the two-capacitor load configuration) for an interrupt period of exactly 1.000000 seconds.
Application Notes
Digital Input Termination During Backup To ensure low current drain during battery backup operation, none of the digital inputs to the ICM7170 should be allowed to float. This keeps the input logic gates out of their transition region, and prevents crossover current from flowing which will shorten battery life. The address, data, CS, and ALE pins should be pulled to either VDD or VSS , and the RD and WR inputs should be pulled to VDD . This is necessary whether the internal battery switchover circuit is used or not. IBM/PC Evaluation Circuit Figure 9 shows the schematic of a board that has been designed to plug into an IBM PC/XT (Note 1) or compatible computer. In this example CS is permanently tied low and access to the chip is controlled by the RD and WR pins. These signals are generated by U1, which gates the IBM's lOR and lOW with a device select signal from U3, which is functioning as an I/O block address decoder. DS1 selects the interrupt priority. U5 is used to isolate the ICM7170 from the PC databus for test purposes. It is only required on heavily-loaded TTL databuses - the ICM7170 can drive most TTL and CMOS databuses directly. Since the IBM PC/XT (Note 1) requires a positive interrupt transition, the ICM7170s interrupt output transistor has been configured as a source follower. As a source follower, the interrupt output signal will swing between 0V and 2.5V. When trimming the oscillator, the frequency counter must be triggered on the rising edge of the interrupt signal.
TABLE 6. BATTERIES Panasonic Rayovac Saronix Statek Seiko NOTE: 1. IBM, IBM PC, and IBM XT are trademarks of IBM Corp. CRYSTALS 32kHz 32kHz 2MHz NTF3238 CX - 1V GT - 38
This three capacitor tuning method will be more stable than the original design and is mandatory for 32kHz tuning fork crystals: without it they may leap into an overtone mode when power is initially applied. The original two-capacitor circuit (Figure 8) will continue to work as well as it always has, and may continue to be used in applications where cost or space is a critical consideration. It is also easier to tune to frequency since one end of the trimmer capacitor is fixed at the AC ground of the circuit (VDD), minimizing the disturbance cause by contact between the adjustment tool and the trimmer capacitor. Note that in both configurations the load capacitors are connected between the oscillator pins and VDD - do not use VSS as an AC ground. Layout: Due to the extremely low current (and therefore high impedance) design of the ICM7170s oscillator, special attention must be given to the layout of this section. Stray capacitance should be minimized. Keep the oscillator traces on a single layer of the PCB. Avoid putting a ground plane above or below this layer. The traces between the crystal, the capacitors, and the ICM7170 OSC pins should be as short as possible. Completely surround the oscillator components with a thick trace of VDD to minimize coupling with any digital signals. The final assembly must be free from contaminants such as solder flux, moisture, or any other potential sources of leakage. A good solder mask will help keep the traces free of moisture and contamination over time. Oscillator Tuning Trimming the oscillator should be done indirectly. Direct monitoring of the oscillator frequency by probing OSC IN or OSC OUT is not accurate due to the capacitive loading of most probes. One way to accurately trim the ICM7170 is by turning on the 1 second periodic interrupt and trimming the oscillator until the interrupt period is exactly one second. This can be done as follows:
1. Turn on the system. Write a 00H to the Interrupt Mask Register (location 10H) to clear all interrupts. 2. Set the Command Register (location 11H) for the appropriate crystal frequency, set the Interrupt Enable and Run/Stop bits to 1, and set the Test bit to 0. 3. Write a 08H to the Interrupt Mask Register to turn on the 1s interrupt. 4. Write an interrupt handler to read the Interrupt Status Register after every interrupt. This resets the interrupt and allows it to be set again. A software loop that reads the Interrupt Status
12-15
ICM7170
C5 A11 AEN S1 S2 S3 S4 1 2 3 4 5 6 7 8 A26 A5 A25 A6 A24 A7 A23 A8 A22 A9 9 10 U3 74LS688 20 19 18 17 16 15 14 13 12 11 7 8 10 9 1 2 3 4 5 6 U1 74LS139 16 15 14 13 12 11 C6 IOR B14 IOW B13
J1 A31 A0 A30 A1 1 2 3 4 5 A29 A2 A28 A3 A27 A4 6 7 8 9 10 C3 C2 B4 IRQ2 B23 IRQ5 B24 IRQ4 B25 IRQ3 S3 TP1 S4 DSI INTERRUPT SELECT R1 1K S1 S2 POSITIVE INTERRUPT X1 C1 11 12 U2 ICM7170 24 23 22 21 20 19 18 17 16 15 14 13 + SR2 B1 1 2 3 4 5 6 7 8 9 10 U5 74LS245 20 19 18 17 16 15 14 13 12 11 D7 A2 D6 A3 D5 A4 D4 A5 D3 A6 D2 A7 D1 A8 D0 A9 C4 C7
R2
D1 OPTIONAL DIODE AND RESISTOR SEE NOTE 8
5V B3.B29 GND B1.B31
FIGURE 9. IBM PC INTERFACE FOR ICM7170Y
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ICM7170 General Notes
1. TIME ACCESS - To update the present time registers (Hex 00 07) the 1/100 register must be read first. The 7 real time counter registers (Hours, Minutes, Seconds, Month, Date, Day, and Year) data are latched only if the 1/100 second counter register is read. The 1/100 seconds data itself is not latched. The real time data will be held in the latches until the 1/100 seconds is read again. See the data sheet section on LATCHED DATA. None of the RAM data is latched since it is static by nature. 2. REGULATED OSClLLATOR - The oscillator's power supply is voltage regulated with respect to VDD . In the 32kHz mode the regulator's amplitude is VTN + VTP (1.8V). In the 1, 2, and 4MHz mode the regulator's amplitude is VTN + VTN + VTP (2.6V). As a result, signal conditioning is necessary to drive the oscillator with an external signal. In addition, it is also necessary to buffer the oscillator's signal to drive other external clocks because of its reduced amplitude and offset voltage. 3. INTERNAL BATTERY BACKUP - When the ICM7170 is using its own internal battery backup circuitry, no other circuitry interfaced to the ICM7170 should be active during standby operation. When VDD (+5V) is turned off (Standby operation), VDD should equal VSS = 0V. All ICM7170 I/O should also equal VSS . At this time, the VBACKUP pin should be 2.8V to 3.5V below VSS when using a Lithium battery. 4. EXTERNAL BATTERY BACKUP - The ICM7170 may be placed on the same power supply as battery-backed up RAM by keeping the ICM7170 in its operational state and having an external circuit switch between system and backup power for the ICM7170 and the RAM. In this case VBACKUP should be pulled up to VDD through a 2K resistor. Although the ICM7170 is always "on" in this configuration, its current consumption will typically be less than a microamp greater than that of standby operation at the same supply voltage (See Note 9). Proper consideration must be given to disabling the ICM7170s and the RAMs I/O before system power is removed. This is important because many microprocessors can generate spurious write signals when their supply falls below their specified operating voltage limits. NANDing CS (or WR) with a POWERGOOD signal will create a CS (or WR) that is only valid when system power is within specifications. The POWERGOOD signal should be generated by an accurate supply monitor such as the ICL7665 under/over voltage detector. An alternate method of disabling the ICM7170's I/O is to pull VBACKUP down to under a volt above VSS (VSS < VBACKUP <1.0V). This will cause the ICM7170 to internally disable all I/O. Do not allow VBACKUP to equal VSS , since this could cause oscillation of the battery backup comparator (See Figure 6). VBACKUP = VSS + 0.5V will disable the I/O and provide enough overdrive for the comparator. 5. ICM7170A PART - The ICM7170A part is binned at final test for a 32.768kHz maximum current of 5A. All other specifications remain the same. 6. INTERRUPTS - The Interrupt Status Register (address 10H) always indicates which of the real time counters have been incremented since the last time the register was read. NOTE: This is independent of whether or not any mask bits are set. The status register is always reset immediately after it is read. If an interrupt from the ICM7170 has occurred since the last time the status register was read, bit D7 of the register will be set. If the source was an alarm interrupt, bit D0 will also be set. If the interrupt transistor has been turned on, reading the Interrupt Status Register will reset it. To enable the periodic interrupt, both the Command Register's Interrupt Enable bit (D4) and at least one bit in the Interrupt Mask Register (D1 - D6) must be set to a 1. The periodic interrupt is triggered when the counter corresponding to a mask bit that has been set is incremented. For example, if you enable the 1 second interrupt when the current value in the 100ths counter is 57, the first interrupt will occur 0.43 seconds later. All subsequent interrupts will be exactly one second apart. The interrupt service routine should then read the Interrupt Status Register to reset the interrupt transistor and, if necessary, determine the cause of the interrupt (periodic, alarm, or non-ICM7170 generated) from the contents of the status register. To enable the alarm interrupts, both the Command Register's Interrupt Enable bit (D4) and the Interrupt Mask Register's Alarm bit (D0) must be set to a 1. Each time there is an exact match between the values in the alarm register and the values in the real time counters, bits D0 and D7 of the Interrupt Status Register will be set to a 1 and the N-channel interrupt transistor will be turned on. As with a periodic interrupt, the service routine should then read the Interrupt Status Register to reset the interrupt transistor and, since periodic and alarm interrupts may be simultaneously enabled, determine the cause of the interrupt if necessary. Mask bits: The ICM7170 alarm interrupt compares the data in the alarm registers with the data in the real time registers, ignoring any registers with the mask bit set. For example, if the alarm register is set to 11-23-95 (Month-Day-Year), 10:59:00:00 (Hour-Minutes-Seconds-Hundredths), and DAY = XX (XX = masked off), the alarm will generate a single interrupt at 10:59 on November 23,1995. If the alarm register is set to 11-XX-95, 10:XX:00:00, and DAY = 2 (2 = Tuesday); the alarm will generate one interrupt every minute from 10:00-10:59 on every Tuesday in November, 1995. NOTE: Masking off the 100ths of a second counter has the same effect as setting it to 00. 7. RESlSTOR IN SERIES WITH BATTERY - A 2K resistor (R2) must be placed in series with the battery backup pin of the ICM7170. The UL laboratories have requested the resistor to limit the charging and discharging current to the battery. The resistor also serves the purpose of degenerating parasitic SCR action. This SCR action may occur if an input is applied to the ICM7170, outside of its supply voltage range, while it is in the standby mode. 8. VBACKUP DIODE - Lithium batteries may explode if charged or if discharged at too high a rate. These conditions could occur if the battery was installed backwards or in the case of a gross component failure. A 1N914-type diode placed in series with the battery as shown in Figure 9 will prevent this from occurring. A resistor of 2M or so should parallel the diode to keep the VBACKUP terminal from drifting toward the VSS terminal and shutting off ICM7170 I/O during normal operation. 9. SUPPLY CURRENT - ICM7170 supply current is predominantly a function of oscillator frequency and databus activity. The lower the oscillator frequency, the lower the supply current. When there is little or no activity on the data, address or control lines, the current consumption of the ICM7170 in its operational mode approaches that of the backup mode.
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