DS17285_1 Datasheet, PDF (13/31 Pages) Maxim Integrated Products – Real-Time Clocks

Real-Time Clocks
The alarm bytes can be used in two ways. First, when
the alarm time is written in the appropriate hours, min-
utes, and seconds alarm locations, the alarm interrupt
is initiated at the specified time each day, if the alarm
enable bit is high. In this mode, the “0” bits in the alarm
registers and the corresponding time registers must
always be written to 0 (see Table 3A and 3B). Writing
the 0 bits in the alarm and/or time registers to 1 can
result in undefined operation.
The second use condition is to insert a “don’t care”
state in one or more of the alarm bytes. The don’t care
code is any hexadecimal value from C0 to FF. The two
most significant bits of each byte set the don’t care
condition when at logic 1. An alarm will be generated
each hour when the “don’t care” bits are set in the
hours byte. Similarly, an alarm is generated every
minute with don’t care codes in the hours and minute
alarm bytes. An alarm is generated every second with
don’t care codes in the hours, minutes, and seconds
alarm bytes.
All 128 bytes can be directly written or read except for
the following:
1) Registers C and D are read-only.
2) Bit 7 of register A is read-only.
3) The MSB of the seconds byte is read-only.
Table 3A. Time, Calendar, and Alarm Data Modes—BCD Mode (DM = 0)
ADDRESS
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
0Dh
Bank 1, 48h
Bank 1, 49h
BIT 7
0
0
0
0
AM/PM
0
AM/PM
0
0
0
0
UIP
SET
IRQF
VRT
BIT 6 BIT 5
BIT 4
10 Seconds
10 Seconds
10 Minutes
10 Minutes
0
10 Hour
0
10 Hour
0
10 Hour
0
10 Hour
0
0
0
0
10 Date
0
0
10 Month
10 Year
DV2
DV1
DV0
PIE
AIE
UIE
PF
AF
UF
0
0
0
10 Century
10 Date
BIT 3
0
RS3
SQWE
0
0
BIT 2 BIT 1
Seconds
Seconds
Minutes
Minutes
BIT 0
FUNCTION
Seconds
Seconds Alarm
Minutes
Minutes Alarm
Hours
Hours
Hours
Day
Date
Month
Year
RS2 RS1 RS0
DM 24/12 DSE
0
0
0
0
0
0
Century
Date
Hours Alarm
Day
Date
Month
Year
Control
Control
Control
Control
Century
Date Alarm
RANGE
00–59
00–59
00–59
00–59
1–12 +AM/PM
00–23
1–12 +AM/PM
00–23
01–07
01–31
01–12
00–99
—
—
—
—
00–99
01–31
Note: Unless otherwise specified, the state of the registers is not defined when power is first applied. Except for the seconds regis-
ter, 0 bits in the time and date registers can be written to 1, but can be modified when the clock updates. 0 bits should always be
written to 0 except for alarm mask bits.
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