DS1305
READING FROM THE CLOCK REGISTERS
Buffers are used to copy the time and date register at the beginning of a read. When reading in burst
mode, the user copy is static while the internal registers continue to increment.
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
01–12 + P/A
01h
81h
Minutes
Hours
12
0
02h
82h
10 Hour
A
10
0
00–23
24
03h
04h
05h
06h
—
83h
84h
85h
86h
—
0
0
0
0
0
0
0
Day
Date
Month
Year
1–7
1–31
01–12
00–99
—
10 Date
10 Month
10 Year
Alarm 0
07h
08h
87h
88h
M
M
10 Seconds Alarm
10 Minutes Alarm
P
Seconds Alarm
Minutes Alarm
00–59
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
0Ch
8Bh
8Ch
M
M
10 Seconds Alarm
10 Minutes Alarm
P
Seconds Alarm
Minutes Alarm
00–59
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
10h
8Eh
8Fh
90h
0
Control Register
Status Register
—
11h
12h–1Fh
20h–7Fh
91h
92h–9Fh
A0h–FFh
Trickle Charger Register
Reserved
—
—
00–FF
96 Bytes User RAM
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 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 registers is set to a logic 1. Similarly, an alarm is generated every minute when bit 7 of the day,
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