The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287. The devices provide a real-time clock/calendar, one time-of-day alarm, three maskable interrupts with a common interrupt output, a programmable square wave, and 114 bytes of battery-backed static RAM (113 bytes in the DS12C887 and DS12C887A). The DS12887 integrates a quartz crystal and lithium energy source into a 24-pin encapsulated DIP package. The DS12C887 adds a century byte at address 32h. For all devices, the date at the end of the month is automatically adjusted for months with fewer than 31 days, including correction for leap years. The devices also operate in either 24-hour or 12-hour format with an AM/PM indicator. A precision temperature-compensated circuit monitors the status of VCC. If a primary power failure is detected, the device automatically switches to a backup supply. A lithium coin-cell battery can be connected to the VBAT input pin on the DS12885 to maintain time and date operation when primary power is absent. The device is accessed through a multiplexed byte-wide interface, which supports both Intel and Motorola modes.
The Maxim DS12885, DS12887 and DS12C887 are drop‑in replacement real‑time clock (RTC) devices for IBM AT computers. They provide calendar functions, alarm, programmable square‑wave output and battery‑backed RAM, with selectable Intel or Motorola bus timing.
The document includes electrical characteristics, pin descriptions, timing diagrams, package outlines and operating limits for industrial and commercial temperature ranges.
| Supply Voltage (VCC) | 4.5 V to 5.5 V |
|---|---|
| Battery Input Voltage (VBAT) | 2.5 V to 4.0 V |
| Operating Temperature Range | -40 °C to +85 °C |
| Data Retention | 10 years |
The devices operate with a supply voltage from 4.5 V to 5.5 V.
The parts are rated up to +85 °C.