Holtek HT1380/HT1381 Serial Timekeeper Chip


Product Overview

Holtek HT1380/HT1381 Serial Timekeeper Chip

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


Microcomputer serial clock
Clock and Calendar


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



Serial timekeeper IC, 8-pin SOP package, RoHS + PB compliant


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