SPI-Compatible RTC with Microprocessor Supervisor, Alarm, and NV RAM Controller

The MAX6916 provides all the features of a real-time clock (RTC) plus a microprocessor supervisory circuit, NV RAM controller, and backup-battery monitor function. In addition, 96 x 8 bits of static RAM are available for scratchpad storage. The MAX6916 communicates with a microprocessor through an SPI™-bus-compatible serial interface.

The real-time clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap years through 2099. The clock operates in either 24hr or 12hr format with an AM/PM indicator. A time/date-programmable alarm function is provided with an open-drain, active-low alarm output.

The microprocessor supervisory circuit features an open-drain, active-low reset available in three different reset thresholds. A manual reset input and a watchdog function are included as well.

The NV RAM controller provides power for external SRAM from a backup battery plus chip-enable gating. The backup battery also provides data retention of the on-board 96 x 8 bits of RAM. An open-drain, active-low, battery-on signal alerts the system when operating from a battery.

The battery-test circuitry periodically tests the backup battery for a low-battery condition. An optional external resistor network selects different battery thresholds. A freshness seal prevents battery drain until the first VCC power-up.

The MAX6916 has a crystal-fail-detect circuit and a data-valid bit. The MAX6916 is available in a 20-pin QSOP package and is guaranteed to operate over the extended temperature range from -40°C to +85°C.

Applications

* Digital Thermostats * Fax Machines * Industrial Control * Intelligent Instruments * Point-of-Sale Equipment * Programmable Logic Controller