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.

Features
■ Automatic battery switchover and WRITE protect for:
– Internal serial RTC and
– External low power SRAM (LPSRAM)
■ 400kHz I2C serial interface
■ 3.0/3.3V operating voltage
–VCC= 2.7 to 3.6V
■ Ultra-low battery supply current of 500nA (max)
■ RoHS compliant
– Lead-free second level interconnect
Serial RTC features
■ 400kHz I2C
■ 44 bytes of general purpose NVRAM
■ Counters for:
– Seconds, minutes, hours, day, date, month, and year
–Century
– 10ths/100ths of seconds
– Clock calibration register allows compensation for crystal variations over temperature
■ Programmable alarm with repeat modes
– Functions in battery back-up mode
■ Power-down timestamp (HT Bit)
■ 2.5 to 5.5V oscillator operating voltage Microprocessor supervisor features
■ Programmable watchdog
– 62.5ms to 128s time-out period
■ Early power-fail warning circuit (PFI/PFO) with 1.25V precision reference
■ Power-on reset/low voltage detect
– Open drain reset output
– Reset voltage, VPFD= 2.60V (nom)
– Two reset input pins
– Watchdog can be steered to reset output