Datasheet

DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM
6 of 18
CLOCK OPERATIONS
Table 2 and the following paragraphs describe the operation of RTC, alarm, and watchdog functions.
Table 2. Register Map
DATA
ADDRESS
B
7
B
6
B
5
B
4
B
3
B
2
B
1
B
0
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.