DS12885 Maxim, DS12885 Datasheet - Page 13

• Manufacturer Part Number: DS12885
• Description: The DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287
• Manufacturer: Maxim

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
Table 2A. Time, Calendar, and Alarm Data Modes—BCD Mode (DM = 0)
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.
ADDRESS
0EH-31H
33H-7FH
0AH
0BH
0CH
0DH
00H
01H
02H
03H
04H
05H
06H
07H
08H
09H
32H
AM/PM
AM/PM
BIT 7
IRQF
SET
VRT
UIP
X
X
0
0
0
0
0
0
0
0
0
BIT 6
DV2
PIE
PF
0
0
0
0
0
0
X
X
10 Century
10 Years
10 Seconds
10 Seconds
10 Minutes
10 Minutes
BIT 5
DV1
AIE
AF
0
0
0
0
0
X
X
10 Hours
10 Hours
10 Date
10 Months
10 Hours
10 Hours
____________________________________________________________________
BIT 4
DV0
UIE
UF
0
0
X
X
SQWE
BIT 3
RS3
0
X
X
0
0
BIT 2
RS2
DM
Seconds
Seconds
0
0
X
X
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.
Minutes
Minutes
Century
Month
Hours
Hours
Date
Year
24/12
BIT 1
RS1
Day
0
0
X
X
Real-Time Clocks
BIT 0
DSE
RS0
X
X
0
0
Seconds Alarm
Minutes Alarm
Hours Alarm
FUNCTION
Seconds
Century*
Minutes
Control
Control
Control
Control
Month
Hours
Date
Year
RAM
RAM
Day
1–12 +AM/PM
1–12 +AM/PM
RANGE
00–59
00–59
00–59
00–59
00–23
00–23
01–07
01–31
01–12
00–99
00–99
—
—
—
—
—
—
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