
DS1306
6 of 22
Figure 2. RTC REGISTERS AND ADDRESS MAP
HEX ADDRESS
READ
WRITE
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
RANGE
00h
80h
0
10 SEC
SEC
00–59
01h
81h
0
10 MIN
MIN
00–59
P
12
A
01–12 + P/A
02h
82h
0
24
10
10-HR
HOURS
00–23
03h
83h
0
DAY
01–07
04h
84h
0
10-DATE
DATE
1–31
05h
85h
0
10-MONTH
MONTH
01–12
06h
86h
10-YEAR
YEAR
00–99
07h
87h
M
10-SEC ALARM 0
SEC ALARM 0
00–59
08h
88h
M
10-MIN ALARM 0
MIN ALARM 0
00–59
P
12
A
01–12 + P/A
09h
89h
M
24
10
10-HR
HOUR ALARM 0
00–23
0Ah
8Ah
M
0
DAY ALARM 0
01–07
0Bh
8Bh
M
10 SEC ALARM 1
SEC ALARM 1
00–59
0Ch
8Ch
M
10 MIN ALARM 1
MIN ALARM 1
00–59
P
12
A
01–12 + P/A
0Dh
8Dh
M
24
10
10-HR
HOUR ALARM 1
00–23
0Eh
8Eh
M
0
DAY ALARM 1
01–07
—
0Fh
8Fh
CONTROL REGISTER
—
10h
90h
STATUS REGISTER
—
11h
91h
TRICKLE CHARGER REGISTER
—
12h–1Fh
92h–
9Fh
RESERVED
—
20h–7Fh
A0h–
FFh
96-BYTES USER RAM
—
Note: Range for alarm registers does not include mask’m’ bits.
The DS1306 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 to 23
hours).
The DS1306 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. Bit 7 of each of the time-of-
day alarm registers are mask bits (Table 2). When all of the mask bits are logic 0, a time-of-day alarm
only occurs 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 is generated every day when bit 7 of the day alarm
register is set to a logic 1. An alarm is generated every hour when bit 7 of the day and hour alarm