Microcomputer interfacing of a real-time clock for data acquisition and control applications

This article describes the interfacing of National Semiconductor's MM58167 real-time clock/calendar to a 6502 microprocessor-based SYM-1 microcomputer. The functions of the clock, details for interfacing to a microcomputer, programming required, and use of its special features are described.A real-time clock/calendar is an essential part of many microcomputer data acquisition and control systems. It provides a 24-hour clock and an accurate interval timer for data acquisition and control functions. The main advantage of a real-time clock is that it keeps track of true time independent of software execution speeds.The MM58167 clock is a CMOS integrated circuit in a 24-pin, dual-in-line package. It is designed for direct connection to the address and data buses of most common microcomputers. This application involved interfacing the clock with a SYM-1 6502-based microcomputer. The clock has eight counters and corresponding latches that contain months through thousands of seconds. The latches can be used for alarm-type functions. Low power battery backup is available through a special ‘power down’ mode. The clock has two interrupt outputs that can be used for control functions.