DS1305
Figure 2. RTC REGISTERS AND ADDRESS MAP
HEX ADDRESS
Bit7 Bit6
Bit5
Bit4
Bit3 Bit2
Bit1
Bit0
RANGE
READ
00H
WRITE
80H
0
0
10 Seconds
10 Minutes
P
Seconds
00–59
00–59
01H
81H
Minutes
01–12 + P/A
12
02H
82H
0
10 Hour
Hours
A
10
0
00–23
24
03H
04H
05H
06H
—
83H
84H
85H
86H
—
0
0
0
0
0
0
0
Day
Date
1–7
1–31
01–12
00–99
—
10 Date
10 Month
10 Year
Month
Year
Alarm 0
07H
87H
M
M
10 Seconds Alarm
10 Minutes Alarm
P
Seconds Alarm
Minutes Alarm
00–59
08H
88H
00–59
12
01–12 + P/A
09H
89H
M
M
10 Hour
Hour Alarm
Day Alarm
A
10
0
24
0
00–23
01–07
—
0AH
8AH
0
—
—
Alarm 1
0BH
8BH
M
M
10 Seconds Alarm
10 Minutes Alarm
P
Seconds Alarm
Minutes Alarm
00–59
0CH
8CH
00–59
12
01–12 + P/A
0DH
8DH
M
M
10 Hour
Hour Alarm
Day Alarm
A
10
0
24
0
00–23
01–07
—
0EH
0FH
8EH
8FH
0
Control Register
Status Register
10H
90H
—
11H
91H
Trickle Charger Register
Reserved
—
12–1FH
20–7FH
92–9FH
A0–FFH
—
96 Bytes User RAM
00–FF
Note: 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 to 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 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 registers is set to a logic 1. Similarly, an alarm is 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 occurs every second.
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DALLAS [ DALLAS SEMICONDUCTOR ]
