bq4822Y RTC Module With 8Kx8 NVSRAM Features General Description ➤ Integrated SRAM, real-time clock, CPU supervisor, crystal, power-fail circuit, and battery The bq4822Y RTC Module is a nonvolatile 65,536-bit SRAM organized as 8192 words by 8 bits with an integral real-time clock and CPU supervisor. The CPU supervisor provides a programmable watchdog timer and a microprocessor reset. Other features include an alarm, power-fail and periodic interrupt, and a battery low warning. ➤ Real-Time Clock counts hundredths of seconds through years in BCD format ➤ RAM-like clock access ➤ Compatible with industrystandard 8K x 8 SRAMs The device combines an internal lithium battery, quartz crystal, clock and power-fail chip, and a full CMOS SRAM in a plastic 28-pin DIP module. The RTC Module directly replaces industry-standard SRAMs and also fits into many EPR O M a n d E E P R O M s o ck e ts without any requirement for special write timing or limitations on the number of write cycles. ➤ Unlimited write cycles ➤ 10-year minimum data retention and clock operation in the absence of power ➤ Automatic power-fail chip deselect and write-protection ➤ Watchdog timer, power-on reset, alarm/periodic interrupt, powerfail and battery-low warning Registers for the real-time clock, alarm and other special functi o n s a re l o ca te d i n re g i s ters 1FF0h–1FFFh of the memory array. The clock and alarm registers are dual-port read/write SRAM locations that are updated once per second by a clock control circuit from the internal clock counters. The dual-port registers allow clock updates to occur without interrupting normal access to the rest of the SRAM array. The bq4822Y also contains a powerfail-detect circuit. The circuit deselects the device whenever VCC falls below tolerance, providing a high degree of data security. The battery is electrically isolated when shipped from the factory to provide maximum battery capacity. The battery remains disconnected until the first application of VCC. ➤ Automatic leap year adjustment ➤ Software clock calibration for greater than ±1 minute per month accuracy Pin Names Pin Connections RST A12 A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 VSS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 28 27 26 25 24 23 22 21 20 19 18 17 16 15 VCC WE INT A8 A9 A11 OE A10 CE DQ7 DQ6 DQ5 DQ4 DQ3 28-Pin DIP Module PN482201.eps May 1997 1 A0–A12 Address input CE Chip enable RST Microprocessor reset WE Write enable OE Output enable DQ0–DQ7 Data in/data out INT Programmable interrupt VCC +5 volts VSS Ground bq4822Y Functional Description including memory and clock interface, data-retention modes, power-on reset timing, watchdog timer activation, and interrupt generation. Figure 1 is a block diagram of the bq4822Y. The following sections describe the bq4822Y functional operation, TimeBase Oscillator Internal Quartz Crystal ÷8 ÷ 64 ÷ 64 16 : 1 MUX Control/Status Registers CE RST Reset and Interupt Generator OE DQ0–DQ7 Clock/Calendar, Alarm and Control Bytes P Bus I/F AD0–AD14 Storage Registers (16 Bytes) WE VCC PowerFail Control Internal Battery INT Control/Calendar Update Storage Registers (8,176 Bytes) Write Protect BD482201.eps Figure 1. Block Diagram Truth Table VCC CE OE WE Mode DQ Power < VCC (max.) VIH X X Deselect High Z Standby VIL X VIL Write DIN Active VIL VIL VIH Read DOUT Active VIL VIH VIH Read High Z Active < VPFD (min.) > VSO X X X Deselect High Z CMOS standby ≤ VSO X X X Deselect High Z Battery-backup mode > VCC (min.) May 1997 2 bq4822Y CE and OE control the state of the eight three--state data I/O signals. If the outputs are activated before tAA, the data lines are driven to an indeterminate state until tAA. If the address inputs are changed while CE and OE remain low, output data remains valid for tOH (output data hold time), but goes indeterminate until the next address access. Address Map The bq4822Y provides 16 bytes of clock and control status registers and 8,176 bytes of storage RAM. Figure 2 illustrates the address map for the bq4822Y. Table 1 is a map of the bq4822Y registers, and Table 2 describes the register bits. Write Mode The bq4822Y is in write mode whenever WE and CE are active. The start of a write is referenced from the latter--occurring falling edge of WE or CE. A write is terminated by the earlier rising edge of WE or CE. The addresses must be held valid throughout the cycle. CE or WE must return high for a minimum of tWR2 from CE or tWR1 from WE prior to the initiation of another read or write cycle. Memory Interface Read Mode The bq4822Y is in read mode whenever OE (output enable) is low and CE (chip enable) is low. The device architecture allows ripple-through access of data from eight of 65,536 locations in the static storage array. Thus, the unique address specified by the 13 address inputs defines which one of the 8,192 bytes of data is to be accessed. Valid data is available at the data I/O pins within tAA (address access time) after the last address input signal is stable, providing that the CE and OE (output enable) access times are also satisfied. If the CE and OE access times are not met, valid data is available after the latter of chip enable access time (tACE) or output enable access time (tOE). 16 Bytes Clock and Control Status Registers Data-in must be valid tDW prior to the end of write and remain valid for tDH1 or tDH2 afterward. OE should be kept high during write cycles to avoid bus contention; although, if the output bus has been activated by a low on CE and OE, a low on WE disables the outputs tWZ after WE falls. 1FFF 1FF0 0 1 2 3 4 5 6 7 8 9 1FEF 8,176 Bytes Storage RAM 10 11 12 13 14 15 0000 Year Month Date Days Hours Minutes Seconds Control Watchdog 1FFF 1FFE 1FFD 1FFC 1FFB 1FFA 1FF9 1FF8 1FF7 Interrupts Alarm Date Alarm Hours 1FF6 1FF5 1FF4 Alarm Minutes 1FF3 Alarm Seconds 1FF2 Tenths/ 1FF1 Hundredths Flags 1FF0 FG482201.eps Figure 2. Address Map May 1997 3 bq4822Y Data-Retention Mode Clock Interface With valid V CC applied, the bq4822Y operates as a conventional static RAM. Should the supply voltage decay, the RAM automatically power-fail deselects, write-protecting itself tWPT after VCC falls below VPFD. All outputs become high impedance, and all inputs are treated as “don't care.” Reading the Clock The interface to the clock and control registers of the bq4822Y is the same as that for the general-purpose storage memory. Once every second, the user-accessible clock/calendar locations are updated simultaneously from the internal real time counters. To prevent reading data in transition, updates to the bq4822Y clock registers should be halted. Updating is halted by setting the read bit D6 of the control register to 1. As long as the read bit is 1, updates to user-accessible clock locations are inhibited. Once the frozen clock information is retrieved by reading the appropriate clock memory locations, the read bit should be reset to 0 in order to allow updates to occur from the internal counters. Because the internal counters are not halted by setting the read bit, reading the clock locations has no effect on clock accuracy. Once the read bit is reset to 0, within one second the internal registers update the user-accessible registers with the correct time. A halt command issued during a clock update allows the update to occur before freezing the data. If power-fail detection occurs during a valid access, the memory cycle continues to completion. If the memory cycle fails to terminate within time t WPT, writeprotection takes place. When VCC drops below VSO, the control circuit switches power to the internal energy source, which preserves data. The internal coin cell maintains data in the bq4822Y after the initial application of VCC for an accumulated period of at least 10 years when VCC is less than VSO. As system power returns and Vcc rises above VSO, the battery is disconnected, and the power supply is switched to external VCC. Write-protection continues for tCER after VCC reaches VPFD to allow for processor stabilization. After tCER, normal RAM operation can resume. Table 1. bq4822Y Clock and Control Register Map Address D7 D6 1FFF D5 D4 D3 D2 10 Years D1 D0 Year 10 Month 00–99 Register Year 1FFE X X 1FFD X X 1FFC X FTE 1FFB X X 1FFA X 1FF9 OSC 1FF8 W R S 1FF7 WDS BM4 BM3 BM2 BM1 1FF6 AIE PWRIE ABE PIE RS3 1FF5 ALM3 X 10-date alarm Alarm date 01–31 1FF4 ALM2 X 10-hour alarm Alarm hours 00–23 Alarm hours 1FF3 ALM1 Alarm 10 minutes Alarm minutes 00–59 Alarm minutes 1FF2 ALM0 Alarm 10 seconds Alarm seconds 00–59 Alarm seconds 1FF1 X Range (h) Month 01–12 Month Date 01–31 Date 10 Date X X X 01–07 Days Hours Day 00–23 Hours 10 Minutes Minutes 00–59 Minutes 10 Seconds Seconds 00–59 Seconds 10 Hours Calibration 0.1 seconds AF PWRF 00–31 BM0 WD1 WD0 RS2 RS1 RS0 0.01 seconds 1FF0 WDF BLF PF Notes: X = Unused bits; can be written and read. Clock/Calendar data in 24-hour BCD format. BLF = 1 for low battery. OSC = 1 stops the clock oscillator. Interrupt enables are cleared on power-up. X X Interrupts 00–99 X Control Watchdog Alarm date 0.1/0.01 seconds Flags May 1997 4 bq4822Y Calibrating the Clock Table 2. Clock and Control Register Bits Bits The bq4822Y real-time clock is driven by a quartz controlled oscillator with a nominal frequency of 32,768 Hz. The quartz crystal is contained within the bq4822Y package along with the battery. The clock accuracy of the bq4822Y module is tested to be within 20ppm or about 1 minute per month at 25°C. The oscillation rates of crystals change with temperature as Figure 3 shows. To compensate for the frequency shift, the bq4822Y offers onboard software clock calibration. The user can adjust the calibration based on the typical operating temperature of individual applications. Description ABE Alarm interrupt enable in battery-backup mode AF Alarm interrupt flag AIE Alarm interrupt enable ALM0–ALM3 Alarm repeat rate BLF Battery-low flag BM0–BM4 Watchdog multiplier FTE Frequency test mode enable OSC Oscillator stop PF Periodic interrupt flag PIE Periodic interrupt enable PWRF Power-fail interrupt flag PWRIE Power-fail interrupt enable R Read clock enable RS0–RS3 Periodic interrupt rate S Calibration sign W Write clock enable WD0–WD1 Watchdog resolution WDF Watchdog flag WDS Watchdog steering The software calibration bits are located in the control register. Bits D0–D4 control the magnitude of correction, and bit D5 the direction (positive or negative) of correction. Assuming that the oscillator is running at exactly 32,786 Hz, each calibration step of D0–D4 adjusts the clock rate by +4.068 ppm (+10.7 seconds per month) or -2.034 ppm (-5.35 seconds per month) depending on the value of the sign bit D5. When the sign bit is 1, positive adjustment occurs; a 0 activates negative adjustment. The total range of clock calibration is +5.5 or -2.75 minutes per month. Two methods can be used to ascertain how much calibration a given bq4822Y may require in a system. The first involves simply setting the clock, letting it run for a month, and then comparing the time to an accurate known reference like WWV radio broadcasts. Based on the variation to the standard, the end user can adjust the clock to match the system's environment even after the product is packaged in a non-serviceable enclosure. The only requirement is a utility that allows the end user to access the calibration bits in the control register. Setting the Clock Bit D7 of the control register is the write bit. Like the read bit, the write bit when set to a 1 halts updates to the clock/calendar memory locations. Once frozen, the locations can be written with the desired information in 24-hour BCD format. Resetting the write bit to 0 causes the written values to be transferred to the internal clock counters and allows updates to the user-accessible registers to resume within one second. 0 Frequency Error -20 Stopping and Starting the Clock Oscillator -40 -60 -80 -100 The OSC bit in the seconds register turns the clock on or off. If the bq4822Y is to spend a significant period of time in storage, the clock oscillator can be turned off to preserve battery capacity. OSC set to 1 stops the clock oscillator. When OSC is reset to 0, the clock oscillator is turned on and clock updates to user-accessible memory locations occur within one second. -120 -30 -20 -10 0 10 20 30 40 50 60 70 Temperature ( C) GR482201 Figure 3. Frequency Error The OSC bit is set to 1 when shipped from the Benchmarq factory. May 1997 5 bq4822Y ally, when the watchdog times out, the watchdog flag bit (WDF) in the flags register, location 1FF0, is set. The second approach uses a bq4822Y test mode. When the frequency test mode enable bit FTE in the days register is set to a 1, and the oscillator is running at exactly 32,768 Hz, the LSB of the seconds register toggles at 512 Hz. Any deviation from 512 Hz indicates the degree and direction of oscillator frequency shift at the test temperature. For example, a reading of 512.01024 Hz indicates a (1E6*0.01024)/512 or +20 ppm oscillator frequency error, requiring ten steps of negative calibration (10*-2.034 or -20.34) or 001010 to be loaded into the calibration byte for correction. To read the test frequency, the bq4822Y must be selected and held in an extended read of the seconds register, location 1FF9, without having the read bit set. The frequency appears on DQ0. The FTE bit must be set using the write bit control. The FTE bit must be reset to 0 for normal clock operation to resume. To reset the watchdog timer, the microprocessor must write to the watchdog register. After being reset by a write, the watchdog time-out period starts over. As a precaution, the watchdog circuit is disabled on a power failure. The user must, therefore, set the watchdog at boot-up for activation. Interrupts The bq4822Y allows four individually selected interrupt events to generate an interrupt request on the INT pin. These four interrupt events are: n The watchdog timer interrupt, programmable to occur according to the time-out period and conditions described in the watchdog timer section. Power-On Reset n The periodic interrupt, programmable to occur once every 122µs to 500ms. The bq4822Y provides a power-on reset, which pulls the RST pin low on power-down and remains low on powerup for tCER after VCC passes VPFD. n The alarm interrupt, programmable to occur once per second to once per month. Watchdog Timer n The power-fail interrupt, which can be enabled to be asserted when the bq4822Y detects a power failure. The watchdog circuit monitors the microprocessor's activity. If the processor does not reset the watchdog timer within the programmed time-out period, the circuit asserts the INT or RST pin. The watchdog timer is activated by writing the desired time-out period into the eight-bit watchdog register described in Table 3 (device address 1FF7). The five bits (BM4–BM0) store a binary multiplier, and the two lower-order bits (WD1–WD0) select the resolution, where 00 = 1 16 second, 01 = 1 4 second, 10 = 1 second, and 11 = 4 seconds. The periodic, alarm, and power-fail interrupts are enabled by an individual interrupt-enable bit in register 1FF6, the interrupts register. When an event occurs, its event flag bit in the flags register, location 1FF0, is set. If the corresponding event enable bit is also set, then an interrupt request is generated. Reading the flags register clears all flag bits and makes INT high impedance. To reset the flag register, the bq4822Y addresses must be held stable at location 1FF0 for at least 50ns to avoid inadvertent resets. The time-out period is the multiplication of the five-bit multiplier with the two-bit resolution. For example, writing 00011 in BM4–BM0 and 10 in WD1–WD0 results in a total time-out setting of 3 x 1 or 3 seconds. A multiplier of zero disables the watchdog circuit. Bit 7 of the watchdog register (WDS) is the watchdog steering bit. When WDS is set to a 1 and a time-out occurs, the watchdog asserts a reset pulse for tCER on the RST pin. During the reset pulse, the watchdog register is cleared to all zeros disabling the watchdog. When WDS is set to a 0, the watchdog asserts the INT pin on a time-out. The INT pin remains low until the watchdog is reset by the microprocessor or a power failure occurs. Addition- Periodic Interrupt Bits RS3–RS0 in the interrupts register program the rate for the periodic interrupt. The user can interpret the interrupt in two ways: either by polling the flags register for PF assertion or by setting PIE so that INT goes active when the bq4822Y sets the periodic flag. Reading the flags register resets the PF bit and returns INT to the high-impedance state. Table 4 shows the periodic rates. Table 3. Watchdog Register Bits MSB Bits LSB 7 6 5 4 3 2 1 0 WDS BM4 BM3 BM2 BM1 BM0 WD1 WD0 May 1997 6 bq4822Y Table 5. Alarm Frequency (Alarm Bits DQ7 of Alarm Registers) Table 4. Periodic Rates RS3 RS2 RS1 RS0 Interrupt Rate ALM3 ALM2 ALM1 ALM0 1 1 1 1 Once per second Alarm Frequency 1 1 1 0 Once per minute when seconds match 1 1 0 0 Once per hour when minutes, and seconds match 1 0 0 0 Once per day when hours, minutes, and seconds match 0 0 0 0 When date, hours, minutes, and seconds match 0 0 0 0 None 0 0 0 1 10ms 0 0 1 0 100ms 0 0 1 1 122.07µs 0 1 0 0 244.14µs 0 1 0 1 488.281µs 0 1 1 0 976.5625 0 1 1 1 1.953125ms 1 0 0 0 3.90625ms 1 0 0 1 7.8125ms 1 0 1 0 15.625ms 1 0 1 1 31.25ms 1 1 0 0 62.5ms 1 1 0 1 125ms 1 1 1 0 250ms Power-Fail Interrupt 1 1 1 1 500ms When V CC falls to the power-fail-detect point, the power-fail flag PWRF is set. If the power-fail interrupt enable bit (PWRIE) is also set, then INT is asserted low. The power-fail interrupt occurs tWPT before the bq4822Y generates a reset and deselects. The PWRIE bit is cleared on power-up. The alarm interrupt can be made active while the bq4822Y is in the battery-backup mode by setting ABE in the interrupts register. Normally, the INT pin tristates during battery backup. With ABE set, however, INT is driven low if an alarm condition occurs and the AIE bit is set. Because the AIE bit is reset during power-on reset, an alarm generated during power-on reset updates only the flags register. The user can read the flags register during boot-up to determine if an alarm was generated during power-on reset. Alarm Interrupt Registers 1FF5–1FF2 program the real-time clock alarm. During each update cycle, the bq4822Y compares the date, hours, minutes, and seconds in the clock registers with the corresponding alarm registers. If a match between all the corresponding bytes is found, the alarm flag AF in the flags register is set. If the alarm interrupt is enabled with AIE, an interrupt request is generated on INT. The alarm condition is cleared by a read to the flags register. ALM3–ALM0 puts the alarm into a periodic mode of operation. Table 5 describes the selectable rates. Battery-Low Warning The bq4822Y checks the internal battery on power-up. If the battery voltage is below 2.2V, the battery-low flag BLF in the flags register is set to a 1 indicating that clock and RAM data may be invalid. May 1997 7 bq4822Y Absolute Maximum Ratings Symbol Parameter Value Unit VCC DC voltage applied on VCC relative to VSS -0.3 to 7.0 V VT DC voltage applied on any pin excluding VCC relative to VSS -0.3 to 7.0 V TOPR Operating temperature 0 to +70 °C TSTG Storage temperature (VCC off; oscillator off) -40 to +70 °C TBIAS Temperature under bias -10 to +70 °C TSOLDER Soldering temperature +260 °C Note: Conditions VT ≤ VCC + 0.3 For 10 seconds Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Functional operation should be limited to the Recommended DC Operating Conditions detailed in this data sheet. Exposure to conditions beyond the operational limits for extended periods of time may affect device reliability. Recommended DC Operating Conditions (TA = TOPR) Symbol Note: Parameter Minimum Typical Maximum Unit VCC Supply voltage 4.5 5.0 5.5 V VSS Supply voltage 0 0 0 V VIL Input low voltage -0.3 - 0.8 V VIH Input high voltage 2.2 - VCC + 0.3 V Notes Typical values indicate operation at TA = 25°C. May 1997 8 bq4822Y DC Electrical Characteristics (TA = TOPR, VCCMIN Symbol Parameter ≤ VCC ≤ VCCMAX) Minimum Typical Maximum Unit Conditions/Notes ILI Input leakage current - - ±1 µA VIN = VSS to VCC ILO Output leakage current - - ±1 µA CE = VIH or OE = VIH or WE = VIL VOH Output high voltage 2.4 - - V IOH = -1.0 mA VOL Output low voltage - - 0.4 V IOL = 2.1 mA IOD RST, INT sink current 10 - - mA VOL = 0.4V ISB1 Standby supply current - 3 6 mA CE = VIH ISB2 Standby supply current - 2 4 mA CE ≥ VCC - 0.2V, 0V ≤ VIN ≤ 0.2V, or VIN ≥ VCC - 0.2V ICC Operating supply current - 55 75 mA Min. cycle, duty = 100%, CE = VIL, II/O = 0mA VPFD Power-fail-detect voltage 4.30 4.37 4.50 V VSO Supply switch-over voltage - 3 - V Notes: Typical values indicate operation at TA = 25°C, VCC = 5V. RST and INT are open-drain outputs. Capacitance (TA = 25°C, F = 1MHz, VCC = 5.0V) Symbol Parameter Minimum Typical Maximum Unit Conditions CI/O Input/output capacitance - - 10 pF Output voltage = 0V CIN Input capacitance - - 10 pF Input voltage = 0V Note: These parameters are sampled and not 100% tested. May 1997 9 bq4822Y AC Test Conditions Parameter Test Conditions Input pulse levels 0V to 3.0V Input rise and fall times 5 ns Input and output timing reference levels 1.5 V (unless otherwise specified) Output load (including scope and jig) See Figures 4 and 5 +5V +5V 1.9k 1.9kΩ DOUT DOUT 1k 100pF 1kΩ FG482202.eps FG482203.eps Figure 4. Output Load A Read Cycle 5pF Figure 5. Output Load B (TA = TOPR, VCCMIN ≤ VCC ≤ VCCMAX) –70 Symbol Parameter Min. Max. Unit 70 - ns Conditions tRC Read cycle time tAA Address access time - 70 ns Output load A tACE Chip enable access time - 70 ns Output load A tOE Output enable to output valid - 35 ns Output load A tCLZ Chip enable to output in low Z 5 - ns Output load B tOLZ Output enable to output in low Z 5 - ns Output load B tCHZ Chip disable to output in high Z 0 25 ns Output load B tOHZ Output disable to output in high Z 0 25 ns Output load B tOH Output hold from address change 10 - ns Output load A May 1997 10 bq4822Y Read Cycle No. 1 (Address Access) 1,2 tRC Address tAA tOH DOUT Previous Data Valid Data Valid TD482201.eps Read Cycle No. 2 (CE Access) 1,3,4 tRC CE tACE tCLZ DOUT tCHZ High-Z High-Z Read Cycle No. 3 (OE Access) 1,5 TD482202.eps tRC Address tAA OE tOE tOHZ tOLZ DOUT Data Valid High-Z High-Z TD482203.eps Notes: 1. WE is held high for a read cycle. 2. Device is continuously selected: CE = OE = VIL. 3. Address is valid prior to or coincident with CE transition low. 4. OE = VIL. 5. Device is continuously selected: CE = VIL. May 1997 11 bq4822Y Write Cycle (TA =TOPR , VCCMIN ≤ VCC ≤ VCCMAX) –70 Symbol Parameter Min. Max. Units Conditions/Notes tWC Write cycle time 70 - ns tCW Chip enable to end of write 55 - ns (1) tAW Address valid to end of write 60 - ns (1) tAS Address setup time 0 - ns Measured from address valid to beginning of write. (2) tWP Write pulse width 50 - ns Measured from beginning of write to end of write. (1) tWR1 Write recovery time (write cycle 1) 0 - ns Measured from WE going high to end of write cycle. (3) tWR2 Write recovery time (write cycle 2) 0 - ns Measured from CE going high to end of write cycle. (3) tDW Data valid to end of write 30 - ns Measured to first low-to-high transition of either CE or WE. tDH1 Data hold time (write cycle 1) 5 - ns Measured from WE going high to end of write cycle. (4) tDH2 Data hold time (write cycle 2) 5 - ns Measured from CE going high to end of write cycle. (4) tWZ Write enabled to output in high Z 0 25 ns I/O pins are in output state. (5) tOW Output active from end of write 5 - ns I/O pins are in output state. (5) Notes: 1. A write ends at the earlier transition of CE going high and WE going high. 2. A write occurs during the overlap of a low CE and a low WE. A write begins at the later transition of CE going low and WE going low. 3. Either tWR1 or tWR2 must be met. 4. Either tDH1 or tDH2 must be met. 5. If CE goes low simultaneously with WE going low or after WE going low, the outputs remain in high-impedance state. May 1997 12 bq4822Y Write Cycle No. 1 (WE-Controlled) 1,2,3 tWC Address tAW tWR2 tCW CE tWP tAS WE tDW DIN tDH2 Data-in Valid tOW tWZ Data Undefined (2) DOUT High-Z TD482204.eps Write Cycle No. 2 (CE-Controlled) 1,2,3,4,5 tWC Address tAW tCW tAS tWR2 CE tWP WE tDW DIN tDH2 Data-in Valid tWZ DOUT Data Undefined (2) High-Z TD482205.eps Notes: 1. CE or WE must be high during address transition. 2. Because I/O may be active (OE low) during this period, data input signals of opposite polarity to the outputs must not be applied. 3. If OE is high, the I/O pins remain in a state of high impedance. 4. Either tWR1 or tWR2 must be met. 5. Either tDH1 or tDH2 must be met. May 1997 13 bq4822Y Power-Down/Power-Up Cycle (TA = TOPR) Minimum Typical Maximum Unit tPF Symbol VCC slew, 4.50 to 4.20 V 300 - - µs tFS VCC slew, 4.20 to VSO 10 - - µs tPU VCC slew, VSO to VPFD (max.) 0 - - µs tCER Chip enable recovery time 40 100 200 ms tDR Data-retention time in absence of VCC 10 - - years tWPT Notes: Parameter Write-protect time 40 100 160 µs Conditions Time during which SRAM is write-protected after VCC passes VFPD on power-up. TA = 25°C. (2) Delay after VCC slews down past VPFD before SRAM is write-protected. 1. Typical values indicate operation at TA = 25°C, VCC = 5V. 2. Battery is disconnected from circuit until after VCC is applied for the first time. tDR is the accumulated time in absence of power beginning when power is first applied to the device. Caution: Negative undershoots below the absolute maximum rating of -0.3V in battery-backup mode may affect data integrity. Power-Down/Power-Up Timing tPF 4.50 VPFD VPFD VCC 4.20 VSO tFS tWPT VSO tPU tDR tCER CE High-Z All Outputs Valid (per Control Inputs) Valid (per Control Inputs) RST INT High-Z TD482206 .eps Notes: 1. PWRIE is set to “1” to enable power fail interrupt. 2. RST and INT are open drain and require an external pull-up resistor. May 1997 14 bq4822Y MA: 28-Pin A-Type Module 28-Pin MA (A-Type Module) Inches Dimension Min. Max. A 0.365 0.375 9.27 9.53 0.015 - 0.38 - B 0.017 0.023 0.43 0.58 C 0.008 0.013 0.20 0.33 D 1.470 1.500 37.34 38.10 E 0.710 0.740 18.03 18.80 e 0.590 0.630 14.99 16.00 G 0.090 0.110 2.29 2.79 L 0.120 0.150 3.05 3.81 S 0.075 0.110 1.91 2.79 bq4822Y MA Speed Options: 70 = 70 ns Package Option: MA = A-type module Device: bq4822Y 8K x 8 Real-Time Clock Module 15 Max. A1 Ordering Information May 1997 Millimeters Min. IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. 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