Datasheet

DS12885/DS12887/DS12887A/DS12C887/DS12C887A
Real-Time Clocks
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The three alarm bytes can be used in two ways. First,
when the alarm time is written in the appropriate hours,
minutes, and seconds alarm locations, the alarm inter-
rupt 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 (Table 2A and 2B). 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 three 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 is 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.
The don’t-care codes in all three alarm bytes create an
interrupt every second.
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 2A. Time, Calendar, and Alarm Data Modes—BCD Mode (DM = 0)
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION RANGE
00H 0 10 Seconds Seconds Seconds 00–59
01H 0 10 Seconds Seconds Seconds Alarm 00–59
02H 0 10 Minutes Minutes Minutes 00–59
03H 0 10 Minutes Minutes Minutes Alarm 00–59
AM/PM 0 10 Hours
04H
0
0
10 Hours
Hours Hours
1–12 +AM/PM
00–23
AM/PM 0 10 Hours
05H
0
0
10 Hours
Hours Hours Alarm
1–12 +AM/PM
00–23
06H 0 0 0 0 0 Day Day 01–07
07H 0 0 10 Date Date Date 01–31
08H 0 0 0 10 Months Month Month 01–12
09H 10 Years Year Year 00–99
0AH UIP DV2 DV1 DV0 RS3 RS2 RS1 RS0 Control —
0BH SET PIE AIE UIE SQWE DM 24/12 DSE Control —
0CH IRQF PF AF UF 0 0 0 0 Control —
0DH VRT 0 0 0 0 0 0 0 Control —
0EH-31H X X X X X X X X RAM —
32H 10 Century Century Century* 00–99
33H-7FH X X X X X X X X RAM —
X = Read/Write Bit.
* DS12C887, DS12C887A only. General-purpose RAM on DS12885, DS12887, and DS12887A.
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 may be modified when the clock updates. 0 bits should always be
written to 0 except for alarm mask bits.