DS1553 64kB, Nonvolatile, Year-2000-Compliant Timekeeping RAM

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CLOCK OPERATIONS

Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions.

Table 2. Register Map

DATA

ADDRESS

FUNCTION/RANGE

1FFFh

10 Year

Year

Year

00-99

1FFEh

X

X

X

10 M

Month

Month

01-12

1FFDh

X

X

10 Date

Date

Date

01-31

1FFCh

X

FT

X

X

X

Day

Day

01-07

1FFBh

X

X

10 Hour

Hour

Hour

00-23

1FFAh

X

10 Minutes

Minutes

Minutes

00-59

1FF9h

OSC

10 Seconds

Seconds

Seconds

00-59

1FF8h

W

R

10 Century

Century

Control

00-39

1FF7h

WDS

BMB

4

BMB3 BMB2

BMB

1

BMB

0

RB

1

RB0

Watchdog

1FF6h

AE

Y

ABE

Y

Y

Y

Y

Y

Interrupts

1FF5h

AM4

Y

10 Date

Date

Alarm Date

01-31

1FF4h

AM3

Y

10 Hours

Hours

Alarm Hours

00-23

1FF3h

AM2

10 Minutes

Minutes

Alarm Minutes

00-59

1FF2h

AM1

10 Seconds

Seconds

Alarm Seconds

00-59

1FF1h

Y

Y

Y

Y

Y

Y

Y

Y

Unused

—

1FF0h

WF

AF

0

BLF

0

0

0

0

Flags

—

X = Unused, Read/Writable Under Write and Read Bit Control

AE = Alarm Flag Enable

FT = Frequency Test Bit

Y = Unused, Read/Writable Without Write and Read Bit Control

OSC = Oscillator Start/Stop Bit

ABE = Alarm in Battery-Backup Mode Enable

W = Write Bit

AM1–AM4 = Alarm Mask Bits

R = Read Bit

WF = Watchdog Flag

WDS = Watchdog Steering Bit

AF = Alarm Flag

BMB0–BMB4 = Watchdog Multiplier Bits

0 = 0 Read Only

RB0–RB1 = Watchdog Resolution Bits

BLF = Battery Low Flag

CLOCK OSCILLATOR CONTROL

The clock oscillator may be stopped at any time. To increase the shelf life of the backup lithium battery

MSB of the Seconds register (B7 of 1FF9h). Setting it to 1 stops the oscillator; setting it to 0 starts the

oscillator. The DS1553 is shipped from Dallas Semiconductor with the clock oscillator turned off, with