Datasheet

9Maxim Integrated
Low-Current I
2
C RTCs for High-ESR Crystals
DS1341/DS1342
the ECLK bit is set. The external clock reference must be
within the defined frequency tolerance prior to initializing
the LOS flag.
Register Map
Table 1 shows the map for the DS1341/DS1342 regis-
ters. During a multibyte access, if the address pointer
reaches the end of the register space (0Fh), it wraps
around to location 00h. On either an I
2
C START or
address pointer incrementing to location 00h, the current
time is transferred to a second set of registers. The time
information is read from these secondary registers while
the clock continues to run. This eliminates the need to
reread the registers in case the main registers update
during a read.
I
2
C Interface
The I
2
C interface is guaranteed to operate when V
CC
is
between 1.8V and 5.5V and the EOSC bit is 0. The I
2
C
interface is accessible whenever V
CC
is at a valid level.
To prevent invalid device operation, the I
2
C interface
should not be accessed when V
CC
is below +1.8V.
If a microcontroller connected to the DS1341/DS1342
resets during I
2
C communications, it is possible that the
microcontroller and the DS1341/DS1342 could become
unsynchronized. When the microcontroller resets, the
DS1341/DS1342 I
2
C interface can be placed into a
known state by holding SCL low for t
TIMEOUT
. Doing so
limits the minimum frequency at which the I
2
C interface
can be operated. If data is being written to the device
Table 1. Register Map
Note: Bits listed as 0 always read back as 0 and cannot be written to a 1.
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 Minutes Minutes Minutes 00–59
02h 0
12/24
AM/PM
10hr Hour Hours
1–12+AM/PM
00–23
10hr
03h 0 0 0 0 0 Day Day 1–7
04h 0 0 10 Date Date Date 01–31
05h CENT 0 0 10 MO Month
Month/
Century
01–12 + Century
06h 10 Year Year Year 00–99
07h A1M1 10 Seconds Seconds
Alarm 1
Seconds
00–59
08h A1M2 10 Minutes Minutes
Alarm 1
Minutes
00–59
09h A1M3
12/24
AM/PM
10hr Hour
Alarm 1
Hours
1–12 + AM/PM
00–23
10hr
0Ah A1M4
DY/DT
10 Date
Day,
Date
Alarm 1 Day,
Alarm 1 Date
1–7
1–31
0Bh A2M2 10 Minutes Minutes
Alarm 2
Minutes
00–59
0Ch A2M3
12/24
AM/PM
10hr Hour
Alarm 2
Hours
1–12 + AM/PM
00–23
10hr
0Dh A2M4
DY/DT
10 Date
Day,
Date
Alarm 2 Day,
Alarm 2 Date
1–7
1–31
0Eh
EOSC
0 EGFIL RS2 RS1 INTCN A2IE A1IE Control —
0Fh OSF DOSF LOS CLKSEL2 CLKSEL1 ECLK A2F A1F
Control/
Status
—