Rainbow Electronics DS1375 - Manual (Page 6)

to location 00h, the current time is transferred to a sec-
ond set of registers. The time information is read from
these secondary registers, while the clock may contin-
ue to run. This eliminates the need to reread the regis-
ters in case the main registers update during a read.
Note: Unless otherwise specified, the state of the regis-
ters is not defined when power is first applied.
Clock and Calendar
The time and calendar information is obtained by read-
ing the appropriate register bytes.
Table 1 shows the
RTC registers. The time and calendar data are set or
initialized by writing the appropriate register bytes. The
contents of the time and calendar registers are in the
binary-coded decimal (BCD) format. The DS1375 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 (20–23 hours). The century bit (bit 7 of the
month register) is toggled when the years register over-
flows from 99 to 00.
The day-of-week register increments at midnight.
Values that correspond to the day of week are user-
defined but must be sequential (i.e., if 1 equals
Sunday, then 2 equals Monday, and so on). Illogical
time and date entries result in undefined operation.
When reading or writing the time and date registers,
secondary (user) buffers are used to prevent errors
when the internal registers update. When reading the
time and date registers, the user buffers are synchro-
nized to the internal registers on any START or STOP
and when the register pointer rolls over to zero. 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.
DS1375
2-Wire Digital Input RTC with Alarm
6 _____________________________________________________________________
Table 1. Timekeeping Registers and SRAM
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
AM/PM
02h 0 12/24
10 Hours
10 Hours Hours Hours
1–12 + AM/PM
00–23
03h 0 0 0 0 0 Day Day 1–7
04h 0 0 10 Date Date Date 00–31
05h Century 0 0
10
Month
Months
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
AM/PM
09h A1M3 12/24
10 Hours
10 Hours Hours Alarm 1 Hours
1–12 + AM/PM
00–23
Day Alarm 1 Day 1–7
0Ah A1M4 DY/DT
10 Date Date Alarm 1 Date 1–31
0Bh A2M2 10 Minutes Minutes Alarm 2 Minutes 00–59
AM/PM
0Ch A2M3 12/24
10 Hours
10 Hours Hours Alarm 2 Hours
1–12 + AM/PM
00–23
— Day Alarm 2 Day 1–7
0Dh A2M4 DY/DT
10 Date Date Alarm 2 Date 1–31
0Eh ECLK CLKSEL1 CLKSEL0 RS2 RS1 INTCN A2IE A1IE Control —
0Fh 0 0 0 0 0 0 A2F A1F
Control/
Status
—
10h–1Fh B7 B6 B5 B4 B3 B2 B1 B0 SRAM 00–FFH