资 源 简 介
The CDP1879 and CDP1879C1 Real-Time Clocks [1] are 24pin devices, each consisting essentially of a long string ofcounters that supply standard clock time and date informationin BCD format, Figure 1. In addition, the CDP1879features an alarm circuit that activates the interrupt outputpin and a separate clock output pin that provides a programmablesquare-wave output signal. Both the internal-alarmand clock-out signals can trigger the interrupt output pin, sothat a status register is available to indicate the interruptsource. Users can supply a signal to the power-down pinthat allows the interrupt-output pin level to control externalpower-down and wake-up circuits. Software generallyrequired by other real-time clocks to prevent clock rollover iseliminated by a transparent “freeze” circuit that assures dataintegrity when accessing the clock. The clock’s counters,plus a control register that regulates operation, areindividually selectable using three address lines. Internalcontrol signals governing read and write operations areselected through the IO/MEM pin, which places the device ina memory-mapped or I/O-mapped mode of operation.
