M41ST85WMH6F Integrated Circuit Chip with 44B NVRAM and 400 kHz I²C Interface Real-Time Clock in SOIC-8 Package
The M41ST85WMH6F is a combination serial real-time clock, microprocessor supervisor, and NVRAM supervisor. Built on a low-power CMOS SRAM process, it features a 64-byte memory space with 44 bytes of NVRAM and 20 memory-mapped RTC registers configured in binary coded decimal (BCD) format.
This device integrates a 400 kHz I²C serial RTC with an automatic backup battery switchover circuit for powering an external LPSRAM and the internal RTC. During power failure, the switchover automatically connects to the backup battery to maintain RTC and external LPSRAM operation. Access to the LPSRAM is also disabled via a chip-enable gate function, providing write-protection for the memory. The microprocessor supervisor section includes a programmable watchdog and power-on reset/low voltage detect function.
| RTC Bus Interface | Serial |
| Date Format | YY-MM-DD-dd |
| Time Format | HH:MM:SS:hh (12 hr, 24 hr) |
| RTC Memory Size | 64 B |
| Package / Case | SOH-28 |
| Battery Backup Switching | Backup Switching |
| Supply Voltage - Min | 2.7 V |
| Supply Voltage - Max | 3.6 V |
| Minimum Operating Temperature | -40 ℃ |
| Maximum Operating Temperature | +85 ℃ |
| Function | Alarm, Calendar, Clock, Supervisor |
| Product Type | Real Time Clocks |
- Automatic battery switchover and WRITE protect for internal serial RTC and external low power SRAM (LPSRAM)
- 400 kHz I²C serial interface
- 3.0/3.3 V operating voltage (VCC = 2.7 to 3.6 V)
- Ultralow battery supply current of 500 nA (max)
- 44 bytes of general purpose NVRAM
- Counters for seconds, minutes, hours, day, date, month, year, century, and tenths/hundredths of seconds
- Clock calibration register for temperature compensation
- Programmable alarm with repeat modes
- Functions in battery back-up mode
- Power-down timestamp (HT bit)
- 2.5 to 5.5 V oscillator operating voltage
- Programmable watchdog with 62.5 ms to 128 s time-out period
- Early power-fail warning circuit with 1.25 V precision reference
- Power-on reset/low voltage detect with open drain reset output
- Battery monitor (battery low flag)
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