LV8572A

LV8572A Real Time Clock (RTC) PRELIMINARY December 1993 LV8572A Low Voltage Real Time Clock (RTC) General Description The LV8572A is intended for use in microprocessor based systems where information is required for multi-tasking data logging or general time of day date information This device is implemented in low voltage silicon gate microCMOS technology to provide low standby power in battery back-up environments The circuit’s architecture is such that it looks like a contiguous block of memory or I O ports The address space is organized as 2 software selectable pages of 32 bytes This includes the Control Registers the Clock Counters the Alarm Compare RAM and the Time Save RAM Any of the RAM locations that are not being used for their intended purpose may be used as general purpose CMOS RAM Time and date are maintained from 1 100 of a second to year and leap year in a BCD format 12 or 24 hour modes Day of week day of month and day of year counters are provided Time is controlled by an on-chip crystal oscillator requiring only the addition of the crystal and two capacitors The choice of crystal frequency is program selectable Power failure logic and control functions have been integrated on chip This logic is used by the RTC to issue a power fail interrupt and lock out the mp interface The time power fails may be logged into RAM automatically when VBB l VCC Additionally two supply pins are provided When VBB l VCC internal circuitry will automatically switch from the main ...