Rainbow Electronics DS1558Y - Manual (Page 7)

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
B
7
B
6
B
5
B
4
B
3
B
2
B
1
B
0
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
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 7FFF9h). Setting OSC to a 1 stops the oscillator; setting to a 0 starts the
oscillator. The initial state of OSC is not guaranteed. When power is applied for the first time, the OSC
bit should be enabled. Oscillator operation and frequency can be verified by setting the FT bit and
monitoring the
IRQ /FT pin for 512Hz.
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.