19-5213; Rev 4; 4/10
Real-Time Clocks
General Description
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
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
V
CC
. 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 V
BAT
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 sup-
ports both Intel and Motorola modes.
Features
♦
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
♦
RAM Clear Function (DS12885, DS12887A, and
♦
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)
♦
Optional Industrial Temperature Range Available
♦
Underwriters Laboratory (UL) Recognized
DS12885/DS12887/DS12887A/DS12C887/DS12C887A
Applications
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
Typical Operating Circuit
CRYSTAL
V
CC
X1
AS
R/W
DS
X2
V
CC
RESET
RCLR
DS83C520
CS
AD(0–7)
IRQ
MOT
SQW
V
BAT
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 Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
