VT82885 datasheet(2/16 Pages) ETC

2 / 16 page

VT82885

Real Time Clock

VIA Technologies, Inc.

WR#

- Write Strobe

RD#

- Read Strobe

RESET#

- Reset Input

IRQ#

- Interrupt Request Output

SQW

- Square Wave Output

VCC

- +5 Volt Supply

GND

- Ground

X1, X2

- 32.768 kHz Crystal Connec-

tions

VBAT#

- +3 Volt Battery Input

RCLR#

- RAM Clear

OPERATION

The block diagram in Figure 1 shows the

pin connections with the major internal func-

tions of the VT82885. The following para-

graphs describe the function of each pin.

FIQURE 1: BLOCK DIAGRAM VT82885

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

OSC

+64

PERIODIC INTERUPT SQUARE WAVE

SELECTOR

SQUARE

WAVE OUT

POWER

SWITCH

AND

WRITE

PROTECT

BUS

INTERFACE

CLOCK/

CALENDAR

UPDATE

BCD/

BINARY

INCREMENT

REGISTERS A,B,C,D

CLOCK, CALENDAR

AND ALARM RAM

USER RAM

114 BYTES

GND

RD#

AD0-

AD7

WR#

VBAT

VCC

CS#

SQW

IRQ#

RESET#

RCLR#

POK

VCC

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