9-5497; Rev 9/10 DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM www.maxim-ic.com FEATURES PIN CONFIGURATIONS Integrated NV SRAM, Real-Time Clock (RTC), Crystal, Power-Fail Control Circuit, and Lithium Energy Source Clock Registers are Accessed Identically to the Static RAM; These Registers Reside in the 16 Top RAM Locations Century Byte Register (i.e.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM PIN DESCRIPTION A0–A14 DQ0–DQ7 IRQ/FT RST CE OE WE VCC GND N.C.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM DESCRIPTION The DS1554 is a full-function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) with an RTC alarm, watchdog timer, power-on reset, battery monitor, and 32k x 8 nonvolatile static RAM. User access to all registers within the DS1554 is accomplished with a byte-wide interface as shown in Figure 1. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour binary-coded decimal (BCD) format.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 1. Block Diagram Maxim DS1554 Table 1.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM DATA-READ MODE The DS1554 is in the read mode whenever CE (chip enable) is low and WE (write enable) is high. The device architecture allows ripple-through access to any valid address location. Valid data will be available at the DQ pins within tAA after the last address input is stable, providing that CE and OE access times are satisfied.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM BATTERY LONGEVITY The DS1554 has a lithium power source that is designed to provide energy for the clock activity, and clock and RAM data retention when the VCC supply is not present. The capability of this internal power supply is sufficient to power the DS1554 continuously for the life of the equipment in which it is installed.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM Table 2.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM SETTING THE CLOCK The 8th bit, B7 of the Control Register is the write bit. Setting the write bit to a 1, like the read bit, halts updates to the DS1554 (7FF8h-7FFFh) registers. After setting the write bit to a 1, RTC Registers can be loaded with the desired RTC count (day, date, and time) in 24-hour BCD format. Setting the write bit to a 0 then transfers the values written to the internal RTC Registers and allows normal operation to resume.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM Table 3. Alarm Mask Bits AM4 1 1 1 1 0 AM3 1 1 1 0 0 AM2 1 1 0 0 0 AM1 1 0 0 0 0 ALARM RATE Once per second When seconds match When minutes and seconds match When hours, minutes, and seconds match When date, hours, minutes, and seconds match When the RTC Register values match Alarm Register settings, the Alarm Flag bit (AF) is set to a 1. If Alarm Flag Enable (AE) is also set to a 1, the alarm condition activates the IRQ/FT pin.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 4. Backup Mode Alarm Waveforms USING THE WATCHDOG TIMER The watchdog timer can be used to detect an out-of-control processor. The user programs the watchdog timer by setting the desired amount of time-out into the 8-bit Watchdog Register (Address 7FF7h).
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground………………………..…………………………………………..-0.3V to +6.0V Storage Temperature Range EDIP ......................………………………………………………………………………………………-40°C to +85°C PowerCap...................…………………..…………………………………………………....................-55°C to +125°C Lead Temperature (soldering, 10s) .....................................................................................................................
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM DC ELECTRICAL CHARACTERISTICS (VCC = 3.3V 10%, TA = Over the operating range.) PARAMETER Active Supply Current TTL Standby Current ( CE = VIH) CMOS Standby Current ( CE VCC - 0.2V) Input Leakage Current (Any Input) Output Leakage Current (Any Output) Output Logic 1 Voltage (IOUT = -1.0 mA) SYMBOL CONDITIONS MIN TYP MAX UNITS ICC (Notes 2, 3, 11) 10 30 mA ICC1 (Notes 2, 3) 0.7 6 mA ICC2 (Notes 2, 3) 0.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM AC CHARACTERISTICS—READ CYCLE (TA = Over the operating range) PARAMETER SYMBOL VCC = 5.0V 10% MIN MAX 70 VCC = 3.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM Figure 6. Write Cycle Timing, Write-Enable Controlled Figure 7.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM POWER-UP/DOWN CHARACTERISTICS—5V (VCC = 5.0V 10%, TA = Over the operating range.) PARAMETER SYMBOL CONDITIONS CE or WE at VIH , Before tPD Power-Down VCC Fall Time: VPF(MAX) to VPF(MIN) tF VCC Fall Time: VPF(MIN) to VSO tFB VCC Rise Time: VPF(MIN) to VPF(MAX) tR tREC VPF to RST High Expected Data-Retention Time (Notes 6, 7) tDR (Oscillator On) Figure 8.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM POWER-UP/DOWN CHARACTERISTICS—3.3V (VCC = 3.3V 10%, TA = Over the operating range.) PARAMETER SYMBOL CONDITIONS CE or WE at VIH , Before tPD Power-Down VCC Fall Time: VPF(MAX) to VPF(MIN) tF VCC Rise Time: VPF(MIN) to VPF(MAX) tR tREC VPF to RST High Expected Data-Retention Time (Notes 6, 7) tDR (Oscillator On) MIN TYP MAX UNITS 0 s 300 0 40 s s ms 200 10 years Figure 9. Power-Up/Down Waveform Timing (3.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM AC TEST CONDITIONS Output Load: 50 pF + 1TTL Gate Input Pulse Levels: 0 to 3.0V Timing Measurement Reference Levels: Input: 1.5V Output: 1.5V Input Pulse Rise and Fall Times: 5 ns NOTES: 1) 2) 3) 4) Voltage referenced to ground. Typical values are at +25C and nominal supplies. Outputs are open. Battery switchover occurs at the lower of either the battery voltage or VPF. 5) The IRQ /FT and RST outputs are open drain.
DS1554 256k, Nonvolatile, Y2K-Compliant Timekeeping RAM REVISION HISTORY REVISION DATE DESCRIPTION PAGES CHANGED 9/10 Updated the Ordering Information table to include only lead-free parts and changed the pinpackage for EMOD to EDIP; updated the Absolute Maximum Ratings section to include the storage temperature range and lead and soldering temperatures for EDIP and PowerCap packages; added Note 11 to the ICC parameter in the DC Electrical Characteristics tables (for 5.0V and 3.
