HT1380/HT1381 is a serial timekeeper IC from Qualcomm. It features wide operating voltage range(2.0V~5.5V), low power consumption(400nA) and support both single byte and burst transmission mode.
The HT1380 (8‑pin DIP) and HT1381 (8‑pin SOP) are low‑power serial timekeeper ICs that keep seconds, minutes, hours, day, date, month and year, with automatic leap‑year handling. They operate in 12‑hour or 24‑hour mode and use a 32768 Hz crystal for timing.
This document includes block diagrams, pin assignments, absolute‑maximum ratings, DC and AC electrical characteristics, register maps, command‑byte definitions, timing diagrams, and example application circuits. It also describes the write‑protect and clock‑halt functions and provides recommended crystal load capacitors.
| Operating Voltage | 2.0 V ~ 5.5 V |
|---|---|
| Maximum Input Serial Clock | 500 kHz at 2 V, 2 MHz at 5 V |
| Input Voltage VIH | 2.0 V (VDD + 0.3 V at 5 V) |
| Operating Temperature | 0 °C ~ 70 °C |
| Package Types | HT1380: 8‑pin DIP, HT1381: 8‑pin SOP |
The HT1380 uses an 8‑pin DIP package.
Serial communication uses three pins: REST, SCLK, and I/O.
Set the D7 bit of the hour register high to enable 12‑hour mode.
When WP is high (logic 1) it prevents writing to any other register.