VT82885 データシートの表示（PDF） - Unspecified

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VT82885

Real Time Clock

Unspecified 

VIA Technologies, Inc.

VT82885

Real Time Clock

WR#

RD#

RESET#

IRQ#

SQW

VCC

- Write Strobe

- Read Strobe

- Reset Input

- Interrupt Request Output

- Square Wave Output

- +5 Volt Supply

OPERATION

The block diagram in Figure 1 shows the

pin connections with the major internal func-

GND

X1, X2

VBAT#

RCLR#

- Ground

- 32.768 kHz Crystal Connec-

tions

- +3 Volt Battery Input

- RAM Clear

tions of the VT82885. The following para-

graphs describe the function of each pin.

FIQURE 1: BLOCK DIAGRAM VT82885

X1

X2

OSC

+8

+64

+64

CS#

VCC

VBAT

POWER

SWITCH

AND

WRITE

PROTECT

VCC

POK

CS#

RD#

WR#

AS

AD0-

AD7

GND

BUS

INTERFACE

PERIODIC INTERUPT SQUARE WAVE

SELECTOR

SQUARE

WAVE OUT

SQW

CLOCK/

CALENDAR

UPDATE

BCD/

BINARY

INCREMENT

REGISTERS A,B,C,D

CLOCK, CALENDAR

AND ALARM RAM

IRQ#

RESET#

USER RAM

114 BYTES

RCLR#

POWER-DOWN/POWER-UP

CONSIDERATIONS

The Real Time Clock function will continue

to operate and all of the RAM, time, calen-

dar and alarm memory locations remain

nonvolatile regardless of the level of the VCC

input. When VCC is applied to the VT82885

and reaches a level of greater than 4.25

volts, the device becomes ac-cessible after

100 ms, provided that the oscillator is

running and the oscillator countdown chain

is not in reset (see Register A). This time

period allows the system to stabilize after

2

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