M41ST85W 3.0/3.3 V I2C combination serial RTC, NVRAM supervisor and microprocessor supervisor Features SNAPHAT battery & crystal Automatic battery switchover and WRITE protect for: – Internal serial RTC and – External low power SRAM (LPSRAM) Ultralow battery supply current of 500 nA (max) RoHS compliant – Lead-free second level interconnect 44 bytes of general purpose NVRAM Counters for: – Seconds, minutes, hours, day, date, month, and year – Century – Tenths/hundredths of seconds – Clock calibration register allows compensation for crystal variations over temperature Power-on reset/low voltage detect – Open drain reset output – Reset voltage, VPFD = 2.60 V (nom) – Two reset input pins – Watchdog can be steered to reset output NVRAM supervisor features Battery monitor (battery low flag) Programmable alarm with repeat modes – Functions in battery back-up mode Non-volatizes external LPSRAM – Automatically switches to back-up battery and deselects (write-protects) external LPSRAM via chip-enable gate – Power-fail deselect (write protect) voltage, VPFD = 2.60 V (nom) – Switchover, VSO = 2.50 V (nom) 2.5 to 5.5 V oscillator operating voltage Microprocessor supervisor features ■ Other features Programmable watchdog – 62.5 ms to 128 s time-out period Early power-fail warning circuit (PFI/PFO) with 1.25 V precision reference Programmable squarewave generator (1 Hz to 32 KHz) Package options: – 28-lead SNAPHAT® IC (SOH28) SNAPHAT battery/crystal top to be ordered separately – 28-lead embedded crystal SOIC (SOX28)

Start data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Stop data transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Data retention mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Setting alarm clock registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Square wave output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Initial power-on defaults . . . . . . . . . . . . . . . . . . . . . . . . . . ....

Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. Table 14. Table 15. Table 16. Table 17. Table 18. Table 19. Table 20. Table 21. Table 22. Signal names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 TIMEKEEPER® register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Alarm repeat modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Logic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 28-pin SOIC connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 28-pin, 300 mil SOIC connections...

Description The M41ST85W is a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor. It is built in a low-power CMOS SRAM process and has a 64-byte memory space with 44 bytes of NVRAM and 20 memory-mapped RTC registers (see Table 2 on page 20). The RTC registers are configured in binary coded decimal (BCD) format. The M41ST85W combines a 400 kHz I2C serial RTC with an automatic backup battery switchover circuit for powering an external LPSRAM as well as the internal RTC. When power begins to fail, the switchover automatically connects to the backup battery to keep...

Description M4T28-BR12SH1 (48 mAh) and M4T32-BR12SH1 (120 mAh). For the extended temperature requirement, the 120 mAh M4T32-BR12SH6 is available. For more information, see Table 21 on page 40. Do not place the SNAPHAT® battery/crystal top in conductive foam, as this will drain the lithium button-cell battery. The 300 mil SOX embedded crystal SOIC typically requires a user-supplied battery for nonvolatile operation. Capacitor backup can also be implemented with this package. Figure 1. 1. For 28-pin, 300 mil embedded crystal SOIC only.

Signal names Conditioned chip enable output External chip enable Interrupt/frequency test/out output (open drain) Power fail input Power fail output Reset output (open drain) Serial clock input Serial data input/output Square wave output Watchdog input Supply voltage Voltage output Battery supply voltage 1. For 28-pin, 300 mil embedded crystal SOIC only. VCC EX IRQ/FT/OUT VOUT NC NC PFI NC SCL NC RST NC SDA ECON

VCC EX IRQ/FT/OUT VOUT NC PFI SCL NC NC RST NC SDA ECON VBAT AI06370d No function (NF) pins should be tied to VSS. Pins 1, 2, 3, and 4 are internally shorted together.

Figure 4. Block diagram REALTIME CLOCK SQUARE WAVE 1. Open drain output. 2. Crystal integrated into SOIC package for MX package option.

Description Hardware hookup Regulator Unregulated Voltage Pushbutton Reset 1. Required for embedded crystal (MX) package only.

Operating modes Operating modes The M41ST85W clock operates as a slave device on the serial bus. Access is obtained by implementing a start condition followed by the correct slave address (D0h). The 64 bytes contained in the device can then be accessed sequentially in the following order: 1. Tenths/hundredths of a second register Seconds register Minutes register Century/hours register Date register Month register Year register Control register 10. Watchdog register 11 - 16. Alarm registers 17 - 19. Reserved 20. Square wave register 21 - 64. User RAM The M41ST85W clock continually monitors VCC...