Rainbow-electronics DS12С887A Manual de usuario descargar pdf (Pagina 1)

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 122ms 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

- +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

DS12C887

Real-Time Clock

www.maxim-ic.com

MOT

DS12C887A

24-Pin Encapsulated Package

AD1

AD3

AD4

AD5

AD6

AD7

GND

SQW

IRQ

RESET

R/W

AD0

AD2

RCLR

1 2

DS12C887 1
Real-Time Clock 1

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Pagina 1 - Real-Time Clock

1 of 2 111901FEATURES§ Drop-in replacement for IBM AT computerclock/calendar§ Pin compatible with the MC146818B andDS1287A§ Totally nonvolatile wit

Pagina 2

DS12C887A2 of 2to clear the RAM, RCLR must be forced to an input logic 0 (-0.3V to +0.8V) during battery-backup modewhen VCC is not applied. The RC

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