TLF9981

May 1993

DP8573A Real Time Clock (RTC)

General Description

The DP8573A is intended for use in microprocessor based

systems where information is required for multi-tasking data

logging or general time of daydate information This device

is implemented in low voltage silicon gate microCMOS tech-

nology to provide low standby power in battery back-up en-

vironments The circuit’s architecture is such that it looks

like a contiguous block of memory or IO ports organized as

one block of 32 bytes This includes the Control Registers

the Clock Counters the Alarm Compare RAM and the Time

Save RAM

Time and date are maintained from 1100 of a second to

year and leap year in a BCD format 12 or 24 hour modes

Day of week and day of month counters are provided Time

is controlled by an on-chip crystal oscillator requiring only

the addition of the 32768 kHz crystal and two capacitors

Power failure logic and control functions have been integrat-

ed on chip This logic is used by the RTC to issue a power

fail interrupt and lock out the mP interface The time power

fails may be logged into RAM automatically when VBB l

VCC Additionally two supply pins are provided When VBB

l

VCC internal circuitry will automatically switch from the

main supply to the battery supply

The DP8573A’s interrupt structure provides three basic

types of interrupts Periodic AlarmCompare and Power

Fail Interrupt mask and status registers enable the masking

and easy determination of each interrupt

Features

Y

Full function real time clockcalendar

1224 hour mode timekeeping

Day of week counter

Parallel resonant oscillator

Y

Power fail features

Internal power supply switch to external battery

Power Supply Bus glitch protection

Automatic log of time into RAM at power failure

Y

On-chip interrupt structure

Periodic alarm and power fail interrupts

Block Diagram

TLF9981 – 1

FIGURE 1

TRI-STATE

is a registered trademark of National Semiconductor Corporation

C1995 National Semiconductor Corporation

RRD-B30M75Printed in U S A