DS1305
RTC REGISTERS Figure 3
RTC Registers DS1305
HEX ADDRESS
READ WRITE
Bit7 Bit6
Bit5
Bit4
Bit3 Bit2 Bit1 Bit0
RANGE
00H
01H
02H
80H
81H
82H
0
0
0
10 SEC
10 MIN
10
P/A
0
SEC
MIN
HOURS
00-59
00-59
01-12 + P/A
00-23
12/2
10 HR
0
4
0
0
0
03H
04H
05H
06H
83H
84H
85H
86H
0
0
0
DAY
DATE
MONTH
YEAR
01-07
1-31
01-12
00-99
10 DATE
10 MONTH
10 YEAR
Alarm 0
07H
08H
09H
87H
88H
89H
M
M
M
10 SEC ALARM
10 MIN ALARM
SEC ALARM
MIN ALARM
HOUR ALARM
00-59
00-59
01-12 + P/A
00-23
12/2
10
P/A
0
10 HR
4
0
0AH
8AH
M
0
DAY ALARM
01-07
Alarm 1
0BH
0CH
0DH
8BH
8CH
8DH
M
M
M
10 SEC ALARM
10 MIN ALARM
SEC ALARM
MIN ALARM
HOUR ALARM
00-59
00-59
01-12 + P/A
00-23
12/2
10
P/A
0
10 HR
4
0
0EH
0FH
10H
11H
8EH
8FH
90H
91H
M
0
DAY ALARM
01-07
CONTROL REGISTER
STATUS REGISTER
TRICKLE CHARGER REGISTER
RESERVED
12-1FH 92-9FH
Range For Alarm Registers Does Not Include Mask’m’ Bits.
The DS1305 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the
12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is
the AM/PM bit with logic high being PM. In the 24-hour mode, bit 5 is the second 10-hour bit (20-23
hours).
The DS1305 contains two time of day alarms. Time of Day Alarm 0 can be set by writing to registers
87h to 8Ah. Time of Day Alarm 1 can be set by writing to registers 8Bh to 8Eh. The alarms can be
programmed (by the INTCN bit of the Control Register) to operate in two different modes - each alarm
can drive its own separate interrupt output or both alarms can drive a common interrupt output. Bit 7 of
each of the time of day alarm registers are mask bits (Table 1). When all of the mask bits are logic 0, a
time of day alarm will only occur once per week when the values stored in timekeeping registers 00h to
03h match the values stored in the time of day alarm registers. An alarm will be generated every day
when bit 7 of the day alarm register is set to a logic 1. An alarm will be generated every hour when bit 7
of the day and hour alarm registers is set to a logic 1. Similarly, an alarm will be generated every minute
when bit 7 of the day, hour and minute alarm registers is set to a logic 1. When bit 7 of the day, hour,
minute and seconds alarm registers is set to a logic 1, alarm will occur every second.
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DALLAS [ DALLAS SEMICONDUCTOR ]
