The low-voltage serial-peripheral interface (SPI?) DS1390/DS1391/DS1394 and the low-voltage 3-wire DS1392/DS1393 real-time clocks (RTCs) are clocks/calendars that provide hundredths of a second, seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. One programmable time-of-day alarm is provided. A temperature-compensated voltage reference monitors the status of V_CC and automatically disables the bus interface and switches to the backup supply if a power failure is detected. On the DS1390, a single open drain output provides a CPU interrupt or a square wave at one of four selectable frequencies. The DS1391 replaces the SQW/active-low INT pin with an active-low RST output/debounced input.

The DS1390, DS1391, and DS1394 are programmed serially through an SPI-compatible, bidirectional bus. The DS1392 and DS1393 communicate over a 3-wire serial bus, and the extra pin is used for either a separate interrupt pin or an active-low RST output/debounced input.

All five devices are available in a 10-pin μSOP package, and are rated over the industrial temperature range.