DS1556 1M, Nonvolatile, Y2K-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

1FFFFh

10 Year

Year

Year

00-99

1FFFEh

X

X

X

10

Month

Month

Month

01-12

1FFFDh

X

X

10 Date

Date

Date

01-31

1FFFCh

X

Ft

X

X

X

Day

Day

01-07

1FFFBh

X

X

10 Hour

Hour

Hour

00-23

1FFFAh

X

10 Minutes

Minutes

Minutes

00-59

1FFF9h

OSC

10 Seconds

Seconds

Seconds

00-59

1FFF8h

W

R

10 Century

Century

Control

00-39

1FFF7h

WDS

BMB4

BMB3

BMB2

BMB1

BMB0

RB1

RB0

Watchdog

1FFF6h

AE

Y

ABE

Y

Y

Y

Y

Y

Interrupts

1FFF5h

AM4

Y

10 Date

Date

Alarm Date

01-31

1FFF4h

AM3

Y

10 Hours

Hours

Alarm Hours

00-23

1FFF3h

AM2

10 Minutes

Minutes

Alarm Minutes

00-59

1FFF2h

AM1

10 Seconds

Seconds

Alarm Seconds

00-59

1FFF1h

Y

Y

Y

Y

Y

Y

Y

Y

Unused

1FFF0h

WF

AF

0

BLF

0

0

0

0

Flags

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

AE = Alarm Flag Enable

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

ABE = Alarm in Battery-Backup Mode Enable

FT = Frequency Test Bit

AM1 to AM4 = Alarm Mask Bits

OSC = Oscillator Start/Stop Bit

WF = Watchdog Flag

W = Write Bit

AF = Alarm Flag

R = Read Bit

0 = 0 (Read Only)

WDS = Watchdog Steering Bit

BLF = Battery Low Flag

BMB0 to BMB4 = Watchdog Multiplier Bits

RB0 to RB1 = Watchdog Resolution Bits

CLOCK OSCILLATOR CONTROL

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

source, the oscillator can be turned off to minimize current drain from the battery. The

OSC bit is the

MSB of the Seconds Register (B7 of 1FFF9h). Setting it to a 1 stops the oscillator, setting to a 0 starts the

oscillator. The DS1556 is shipped from Maxim with the clock oscillator turned off,

OSC bit set to a 1.