The HT1380A/HT1381A 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 HT1380A/HT1381A 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 HT1380A/HT1381A 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 HT1380A/HT1381A use a serial I/O transmission method to interface with a microprocessor. Only three wires are required: (1) RESTB, (2) SCLK and (3) I/O. Data can be delivered 1 byte at a time or in a burst of up to 8 bytes.

• Operating voltage: 2.0V~5.5V
• Maximum input serial clock:
  500kHz at V_DD=2V, 2MHz at V_DD=5V
• Operating current:
  less than 0.5uA at 2V
  less than 0.7uA at 3V
  less than 1.0uA at 5V
• TTL compatible
  - V_IH: 2.0V ~ V_DD 0.3V at V_DD=5V
  - V_IL: 0.3V ~ 0.8V at V_DD=5V
• Two data transmission modes: single-byte or burst mode
• Serial I/O transmission
• All registers store BCD format
• HT1380A: 8-pin DIP package
  HT1381A: 8-pin SOP package