Features
Operating voltage: 2.0V~5.5V
Maximum input serial clock: 500kHz at VDD=2V,
2MHz at VDD=5V
Operating current: less than 1A at 2V,
less than 1.2A at 5V
TTL compatible
 VIH: 2.0V~VDD+0.3V at VDD=5V
 VIL: 0.3V~+0.8V at VDD=5V
Two data transmission modes: single-byte,
or burst mode
Serial I/O transmission
All registers store BCD format
HT1380: 8-pin DIP package
HT1381: 8-pin SOP package

General Description
The HT1380/HT1381 is a serial timekeeper IC which
provides seconds, minutes, hours, day, date, month and
year information. The number of days in each month
and leap years are automatically adjusted. The
HT1380/HT1381 is designed for low power consumption
and can operate in two modes: one is the 12-hour
mode with an AM/PM indicator, the other is the 24-hour
mode.
The HT1380/HT1381 has several registers to store the
corresponding information with 8-bit data format. A
32768Hz crystal is required to provide the correct timing.
In order to minimize the pin number, the
HT1380/HT1381 use a serial I/O transmission method
to interface with a microprocessor. Only three wires are
required: (1) REST, (2) SCLK and (3) I/O. Data can be
delivered 1 byte at a time or in a burst of up to 8 bytes.