Dallas Semiconductor DS12887A Datasheet

A

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DS12887A

Real-Time Clock

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 leap­year compensation valid up to 2100

§ Binary or BCD representation of time,

calendar, and alarm

§ 12-hour 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
– 14 bytes of clock and control registers
– 114 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 122ms to 500ms
– End-of-clock update cycle

§ Underwriters Laboratory (UL) recognized

PIN ASSIGNMENT (Top View)

MOT
N.C.
N.C.
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7

GND

1

2
3
4

5
6

7
8

9
10

11
12

DS12887A

24 PDIP Module (700mil)

Package Dimension Information

http://www.maxim-ic.com/TechSupport/DallasPackInfo.htm

24
23

22
21

20
19

18
17

16
15

14
13

V

CC

SQW
NC

RCLR
N.C.

IRQ
RESET
DS
N.C.
R/W

S

CS

PIN DESCRIPTION

AD0–AD7 - Multiplexed Address/Data Bus
N.C. - No Connect
MOT - Bus Type Selection

CS - RTC Chip-Select Input

AS - Address Strobe

W - Read/Write Input

R/

DS - Data Strobe

RESET - Reset Input

IRQ - Interrupt Request Output

SQW - Square-Wave Output
V

CC

RCLR - RAM Clear

GND - Ground

- +5V Main Supply

ORDERING INFORMATION

PART PIN-PACKAGE TOP MARK TEMP RANGE

DS12887A 24 PDIP Module DS12887A 0°C to +70°C

Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: http://www.maxim-ic.com/errata.

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DS12887A

DESCRIPTION

The DS12887A real-time clock plus RAM is designed to be a direct replacement for the DS1287A. The
DS12887A is identical in form, fit, and function to the DS1287A, and includes 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 114

bytes of general-purpose RAM but does not affect the RAM associated with the real-time clock. In order

to clear the RAM,

when V

is not applied. The RCLR function is designed to be used by human interface (shorting to

CC

RCLR must be forced to an input logic 0 (-0.3V to +0.8V) during battery-backup mode

ground manually or by switch) and not to be driven with external buffers.

For a complete description of operating conditions, electrical characteristics, bus timing and pin

descriptions other than

Note: Pins 2, 3, 16, 20, and 22 are missing by design. This device cannot be stored or shipped in conductive material that will give a continuity
path between the RAM clear pin and ground.

RCLR , refer to the DS12887 data sheet.

TYPICAL OPERATING CIRCUIT

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