BQ4285S 查看數據表（PDF） - Unspecified

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BQ4285S

Real-Time Clock (RTC) With NVRAM Control

Unspecified 

bq4285

Real-Time Clock (RTC) With NVRAM Control

Features

® Direct clock/calendar replace-

ment for IBM® AT-compatible

computers and other applications

® Functionally compatible with the

DS1285

- Closely matches MC146818A

pin configuration

® 114 bytes of general nonvolatile

storage

® Automatic backup and write-

protect control to external SRAM

® 160 ns cycle time allows fast bus

operation

® Selectable Intel or Motorola bus

timing (PLCC), Intel bus timing

(DIP and SOIC)

® Less than 0.5 µA load under bat-

tery operation

® 14 bytes for clock/calendar and

control

Pin Connections

VOUT 1

X1 2

X2 3

AD0 4

AD1 5

AD2 6

AD3 7

AD4 8

AD5 9

AD6 10

AD7 11

VSS 12

24 VCC

23 SQW

22 CEOUT

21 CEIN

20 BC

19 INT

18 RST

17 DS

16 VSS

15 R/W

14 AS

13 CS

24-Pin DIP or SOIC

PN428501.eps

Jan. 1999 D

® Calendar in day of the week, day of

the month, months, and years, with

automatic leap-year adjustment

® Time of day in seconds, minutes,

and hours

- 12- or 24-hour format

- Optional daylight saving

adjustment

® BCD or binary format for clock

and calendar data

® Programmable square wave out-

put

® Three individually maskable in-

terrupt event flags:

- Periodic rates from 122 µs to

500 ms

- Time-of-day alarm once per

second to once per day

- End-of-clock update cycle

® 24-pin plastic DIP or SOIC

AD0 5

AD1 6

AD2 7

AD3 8

AD4 9

AD5 10

NC 11

25 CEIN

24 BC

23 INT

22 RST

21 DS

20 VSS

19 R/ W

28-Pin PLCC

PN428502.eps

General Description

The CMOS bq4285 is a low-power

microprocessor peripheral providing

a time-of-day clock and 100-year cal-

endar with alarm features and bat-

tery operation. Other features include

three maskable interrupt sources,

square wave output, and 114 bytes of

general nonvolatile storage.

The bq4285 write-protects the clock,

calendar, and storage registers dur-

ing power failure. A backup battery

then maintains data and operates

the clock and calendar.

The bq4285 is a fully compatible real-

time clock for IBM AT-compatible com-

puters and other applications. The only

external components are a 32.768kHz

crystal and a backup battery.

The bq4285 integrates a battery-

backup controller to make a standard

CMOS SRAM nonvolatile during

power-fail conditions. During power-

fail, the bq4285 automatically write-

protects the external SRAM and pro-

vides a VCC output sourced from the

clock backup battery.

Pin Names

AD0–AD7

MOT

CS

AS

DS

R/W

INT

RST

SQW

BC

X1–X2

NC

CEIN

CEOUT

VOUT

VCC

VSS

Multiplexed address/data

input/output

Bus type select input

(PLCC only )

Chip select input

Address strobe input

Data strobe input

Read/write input

Interrupt request output

Reset input

Square wave output

3V backup cell input

Crystal inputs

No connect

RAM chip enable input

RAM chip enable output

Supply output

+5V supply

Ground

1

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