CDP68HC68T1 pdf datasheet(CMOS

The CDP68HC68T1 Real-Time Clock provides a
time/calendar function, a 32 byte static RAM, and a 3 wire
Serial Peripheral Interface (SPI Bus). The primary function of
the clock is to divide down a frequency input that can be
supplied by the on-board oscillator in conjunction with an
external crystal or by an external clock source. The internal
oscillator can operate with a 32kHz, 1MHz, 2MHz, or 4MHz
crystal. An external clock source with a 32kHz, 1MHz, 2MHz,
4MHz, 50Hz or 60Hz frequency can be used to drive the
CDP68HC68T1. The time registers hold seconds, minutes,
and hours, while the calendar registers hold day-of-week,
date, month, and year information. The data is stored in BCD
format. In addition, 12 or 24 hour operation can be selected.
In 12 hour mode, an AM/PM indicator is provided. The T1
has a programmable output which can provide one of seven
outputs for use elsewhere in the system.