MM58274CN

The MM58274CN is one member of the MM58274C series.It has the following features including (1)timekeeping from tenths of seconds to tens of years in independently accessible registers;(2)buffered crystal frequency output in test mode for easy oscillator setting;(3)independent interrupting time with open drain output.

The MM58274CN is fabricated using low threshold metal gate CMOS technology and is designed to operate in bus oriented microprocessor systems where a real time clock and calendar function are required. The on-chip 32.768 kHz crystal controlled oscillator will maintain timekeeping down to 2.2V to allow low power standby battery operation. This device is pin compatible with the MM58174A but continues timekeeping up to tens of years. The MM58274CN is a direct replacement for the MM58274 offering improved Bus access cycle times.The MM58274C is a bus oriented microprocessor real time clock. It has the same pin-out as the MM58174A while offering extended timekeeping up to units and tens of years. To enhance the device further, a number of other features have been added including: 12 or 24 hours counting, a testable data-changed flag giving easy error-free time reading and simplified interrupt control.

Writing a logic 1 to the clock start/stop control bit of MM58274CN resets the internal oscillator divider chain and the tenths of seconds counter. Writing a logic 0 will start the clock timing from the nearest second. The time then updates every 100 ms with all counters changing synchronously. Time changing during a read is detected by testing the data-changed bit of the control register after completing a string of clock register reads.Interrupt delay times of 0.1s, 0.5s, 1s, 5s, 10s, 30s or 60s can be selected with single or repeated interrupt outputs.The open drain output of MM58274CN is pulled low whenever the interrupt timer times out and is cleared by reading the control register.The counters are arranged as 4-bit words and can be randomly accessed for time reading and setting. The counters output in BCD (binary coded decimal) 4-bit numbers. Any register of MM58274CN which has less than 4 bits (e.g., days of week uses only 3 bits) will return a logic 0 on any unused bits. When written to, the unused inputs will be ignored.