Clock/Supervisor Integrates Crystal

The latest version of the M41ST85 serial real-time clock (RTC) and supervisor chip includes a 32 kHz crystal and comes in a SOX28 package measuring 18.4 mm x 10.42 mm and 2.4 mm in height. Available with 3V and 5V operating voltages, the device combines a serial RTC with a microprocessor and NVRAM supervisor functions. Accessed via a 400 kHz I2C interface, the programmable, battery-backed RTC section contains counters that track time and date with a resolution ranging from hundredths of a second up to a century. It is organized as 64 x 8 bits, of which 44 bytes are general-purpose NVRAM and the other 20 bytes are the RTC registers. The NVRAM supervisor includes an automatic battery switchover circuit, chip-enable gate, and a battery monitor. The microprocessor section includes an early power-fail warning circuit, a 1.25V reference, and a reset circuit that can be triggered by multiple sources. Other features of the device include a watchdog timer that can also be configured as a reset source and is programmable for timeout periods ranging from 62.5 ms to 128s. Price is $2.39 each/10,000. STMICROELECTRONICS, INC., Lexington, MA. (781) 861-2650.