DS1390 Maxim, DS1390 Datasheet - Page 15

• Manufacturer Part Number: DS1390
• Description: The low-voltage serial-peripheral interface (SPI™) DS1390/DS1391/DS1394 and the low-voltage 3-wire DS1392/DS1393 real-time clocks (RTCs) are clocks/calendars that provide hundredths of a second, seconds, minutes, hours, day, date, month, and ye
• Manufacturer: Maxim

The hundredths-of-seconds generator circuit shown in
the functional diagram is a state machine that divides
the incoming frequency (4096Hz) by 41 for 24 cycles
and 40 for one cycle. This produces a 100Hz output
that is slightly off during the short term, and is exactly
correct every 250ms. The divide ratio is given by:
Thus, the long-term average frequency output is
exactly the desired 100Hz.
The time and calendar information is obtained by read-
ing the appropriate register bytes. See Table 3 for the
RTC registers. The time and calendar are set or initial-
Table 3. Address Map (continued)
Note: Unless otherwise specified, the state of the registers is not defined when power (V
X = General-purpose read/write bit.
0 = Always reads as zero.
ADDRESS
WRITE
8Bh
8Ch
8Dh
8Eh
8Fh
Ratio = [41 x 24 + 40 x 1] / 25 = 40.96
ADDRESS
READ
0Bh
0Ch
0Dh
0Eh
0Fh
Hundredths-of-Seconds
EOSC
BIT 7
TCS3
Clock and Calendar
AM3
AM4
OSF
DY/DT
12/24
BIT 6
TCS2
Low-Voltage SPI/3-Wire RTCs with
0
0
0
0
____________________________________________________________________
Generator
10 Hour
AM/PM
BBSQI
BBSQI
TCS1
BIT 5
X
0
10 Date
BIT 4
TCS0
Hour
RS2
RS2
10
X
0
BIT 3
RS1
RS1
DS1
X
0
ized by writing the appropriate register bytes. The con-
tents of the time and calendar registers are in the bina-
ry-coded decimal (BCD) format. 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. The DS1390–DS1393 can
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 to 23 hours). Changing the 12/24-hour mode-
select bit requires that the hours data be re-entered,
including the alarm register (if used). The century bit
(bit 7 of the month register) is toggled when the years
register overflows from 99 to 00.
INTCN
ESQW
BIT 2
DS0
X
0
Hour
Date
Day
ROUT1 ROUT0
BIT 1
0
0
0
0
CC
Trickle Charger
and V
BIT 0
AIE
AIE
AF
X
BACKUP
Alarm Hours
Alarm Date
FUNCTION
Alarm Day
Charger
) is first applied.
Control
Trickle
Status
DS1390/93/94
00–23 BCD
01–31 BCD
1–7 BCD
RANGE
DS1391
DS1392
1–12 +
AM/PM
—
—
15