Rainbow Electronics DS12С887A - Manual

1 of 2 111901
FEATURES
§ Drop-in replacement for IBM AT computer
clock/calendar
§ Pin compatible with the MC146818B and
DS1287A
§ Totally nonvolatile with over 10 years of
operation in the absence of power
§ Self-contained subsystem includes lithium,
quartz, and support circuitry
§ Counts seconds, minutes, hours, days, day of
the week, date, month, and year with leap-
year compensation valid up to 2100
§ Binary or BCD representation of time,
calendar, and alarm
§ 12- or 24-hour clock with AM and PM in 12-
hour mode
§ Daylight Savings Time option
§ Selectable between Motorola and Intel bus
timing
§ Multiplex bus for pin efficiency
§ Interfaced with software as 128 RAM
locations
– 15 bytes of clock and control registers
– 113 bytes of general purpose RAM
§ Programmable square-wave output signal
§ Bus-compatible interrupt signals (IRQ)
§ Three interrupts are separately software-
maskable and testable
– Time-of-day alarm once/second to
once/day
– Periodic rates from 122 ms to 500ms
– En-of-clock update cycle
§ Century register
PIN ASSIGNMENT
PIN DESCRIPTION
AD0–AD7 - Multiplexed Address/Data Bus
NC
- No Connect
MOT - Bus Type Selection
CS - RTC Chip Select Input
AS - Address Strobe
R/ W - Read/Write Input
DS - Data Strobe
RESET - Reset Input
IRQ - Interrupt Request Output
SQW - Square-Wave Output
V
CC
- +5V Main Supply
RCLR - RAM Clear
GND - Ground
DESCRIPTION
The DS12C887A real-time clock plus RAM is designed to be a direct upgrade replacement for the
DS12887A in existing IBM-compatible personal computers to add hardware year-2000 compliance. A
century byte was added to memory location 50, 32h, as called out by the PC AT specification. The
DS12C887A is identical in form, fit, and function to the DS1287A, and provides additional 64 bytes of
general-purpose RAM. Access to this additional RAM space is determined by the logic level presented on
AD6 during the address portion of an access cycle. The
RCLR pin is used to clear (set to logic 1) all 113
bytes of general purpose RAM but does not affect the RAM associated with the real time clock. In order
DS12C887A
Real-Time Clock
www.maxim-ic.com
MOT 1
2
3
4
5
6
7
8
9
10
11
12
23
DS12C887A
24-Pin Encapsulated Package
NC
AD1
AD3
AD4
AD5
AD6
AD7
GND
V
CC
SQW
NC
NC
IRQ
RESET
DS
NC
R/W
AS
CS
24
22
21
20
19
18
17
16
15
14
13
NC
AD0
AD2
RCLR