Rev 3; 2/07
Real-Time Clock
5/DS12C87A
General Description
Features
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
♦ 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
V
. If a primary power failure is detected, the device
CC
automatically switches to a backup supply. A lithium
coin-cell battery can be connected to the V input
♦ 114 Bytes of General-Purpose, Battery-Backed
RAM (113 Bytes in the DS12C887 and
DS12C887A)
BAT
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 sup-
ports both Intel and Motorola modes.
♦ RAM Clear Function (DS12885, DS12887A, and
DS12C887A)
Applications
♦ Interrupt Output with Three Independently
Embedded Systems
Utility Meters
Maskable Interrupt Flags
♦ Time-of-Day Alarm Once Per Second to Once
Security Systems
Per Day
Network Hubs, Bridges, and Routers
♦ Periodic Rates from 122μs to 500ms
♦ End-of-Clock Update Cycle Flag
Typical Operating Circuit
♦ Programmable Square-Wave Output
♦ Automatic Power-Fail Detect and Switch Circuitry
CRYSTAL
V
CC
♦ Optional 28-Pin PLCC Surface Mount Package or
X1
AS
X2
V
CC
32-Pin TQFP (DS12885)
RESET
RCLR
♦ Optional Encapsulated DIP (EDIP) Package with
Integrated Crystal and Battery (DS12887,
DS12887A, DS12C887, DS12C887A)
R/W
DS
DS83C520
DS12885
CS
♦ Optional Industrial Temperature Range Available
♦ Underwriters Laboratory (UL) Recognized
AD(0–7)
IRQ
SQW
V
BAT
MOT
GND
Pin Configurations and Ordering Information appear at end of data sheet.
______________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.