DS1558

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CLOCK OPERATIONS

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

Table 2. DS1558 REGISTER MAP

DATA

ADDRESS

FUNCTION/RANGE

7FFFFh

10 YEAR

YEAR

YEAR

00–99

7FFFEh

X

X

X

10 M

MONTH

MONTH

01–12

7FFFDh

X

X

10 DATE

DATE

DATE

01–31

7FFFCh

X

FT

X

X

X

DAY

DAY

01–07

7FFFBh

X

X

10 HOUR

HOUR

HOUR

00–23

7FFFAh

X

10 MINUTES

MINUTES

MINUTES

00–59

7FFF9h

OSC

10 SECONDS

SECONDS

SECONDS

00–59

7FFF8h

W

R

10 CENTURY

CENTURY

CONTROL

00–39

7FFF7h

WDS

BMB4

BMB3

BMB2

BMB1

BMB0

RB1

RB0

WATCHDOG

—

7FFF6h

AE

Y

ABE

Y

Y

Y

Y

Y

INTERRUPTS

—

7FFF5h

AM4

Y

10 DATE

DATE

ALARM DATE

01–31

7FFF4h

AM3

Y

10 HOURS

HOURS

ALARM HOURS

00–23

7FFF3h

AM2

10 MINUTES

MINUTES

ALARM MINUTES

00–59

7FFF2h

AM1

10 SECONDS

SECONDS

ALARM SECONDS

00–59

7FFF1h

Y

Y

Y

Y

Y

Y

Y

Y

UNUSED

—

7FFF0h

WF

AF

0

BLF

0

0

0

0

FLAGS

—

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

AE = Alarm Flag Enable

FT = Frequency Test Bit

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

OSC = Oscillator Start/Stop Bit

ABE = Alarm in Backup-Battery Mode Enable

W = Write Bit

AM1–AM4 = Alarm Mask Bits

R = Read Bit

WF = Watchdog Flag

WEN = Watchdog Enable Bit

AF = Alarm Flag

BMB0–BMB4 = Watchdog Multiplier Bits

0 = Reads as a 0 and Cannot Be Changed

RB0–RB1 = Watchdog Resolution Bits

BLF = Battery Low Flag

CLOCK OSCILLATOR CONTROL

bit should be enabled. Oscillator operation and frequency can be verified by setting the FT bit and

OSCILLATOR STARTUP TIME

Oscillator startup times are highly dependent upon crystal characteristics and layout. High ESR and

excessive capacitive loads are the major contributors to long startup times. A circuit using a crystal with

the recommended characteristics and following the recommended layout usually starts within 1 second.