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.
Key Features
Applications/Uses
Drop-In Replacement for IBM AT Computer Clock/Calendar
RTC Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year Compensation Through 2099
Binary or BCD Time Representation
12-Hour or 24-Hour Clock with AM and PM in 12-Hour Mode
Daylight Saving Time Option
Selectable Intel or Motorola Bus Timing
Interfaced with Software as 128 RAM Locations
14 Bytes of Clock and Control Registers
114 Bytes of General-Purpose, Battery-Backed RAM (113 Bytes in the DS12C887 and DS12C887A)
RAM Clear Function (DS12885, DS12887A, and DS12C887A)
Interrupt Output with Three Independently Maskable Interrupt Flags
Time-of-Day Alarm Once Per Second to Once Per Day
Periodic Rates from 122µs to 500ms
End-of-Clock Update Cycle Flag
Programmable Square-Wave Output
Automatic Power-Fail Detect and Switch Circuitry
Optional 28-Pin PLCC Surface Mount Package or 32-Pin TQFP (DS12885)
Optional Encapsulated DIP (EDIP) Package with Integrated Crystal and Battery (DS12887, DS12887A, DS12C887, DS12C887A)
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