Rainbow-electronics DS1393 Uživatelský manuál stáhnout pdf (Strana 14)

DS1390/DS1391/DS1392/DS1393

Hundredths-of-Seconds

Generator

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:

Ratio = [41 x 24 + 40 x 1] / 25 = 40.96

Thus, the long-term average frequency output is

exactly the desired 100Hz.

Clock and Calendar

The time and calendar information is obtained by read-

ing the appropriate register bytes. See Table 2 for the

RTC registers. The time and calendar are set or initial-

ized by writing the appropriate register bytes. The con-

tents of the time and calendar registers are in the

binary-coded decimal (BCD) format. The day-of-week

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

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

Alarms

All four devices contain one time-of-day/date alarm.

Writing to registers 88h through 8Ch sets the alarm.

The alarm can be programmed (by the alarm enable

and INTCN bits of the control register) to activate the

SQW/INT or INT output on an alarm-match condition.

The alarm can activate the SQW/INT or INT output while

the device is running from V

BACKUP

if BBSQI is

enabled. Bit 7 of each of the time-of-day/date alarm

registers are mask bits (Table 3). When all the mask

bits for each alarm are logic 0, an alarm only occurs

when the values in the timekeeping registers 00h to 06h

match the values stored in the time-of-day/date alarm

registers. The alarms can also be programmed to

repeat every second, minute, hour, day, or date. Table

3 shows the possible settings. Configurations not listed

in the table result in illogical operation.

Low-Voltage SPI/3-Wire RTCs with

Trickle Charger

14 ____________________________________________________________________

ALARM REGISTER MASK BITS (BIT 7)

08H

DY/DT

AM4 AM3 AM2 AM1

ALARM RATE

FFh X 1 1 1 1 Alarm every 1/100th of a second

F[0–9]h X 1 1 1 1 Alarm when hundredths of seconds match

[0–9][0–9]

X1 111Alarm when tenths, hundredths of seconds match

[0–9][0–9]

X1 110

Alarm when seconds, tenths, and hundredths of seconds

match

[0–9][0–9]

X1 100

Alarm when minutes, seconds, tenths, and hundredths of

seconds match

[0–9][0–9]

X1 000

Alarm when hours, minutes, seconds, tenths, and hundredths

of seconds match

[0–9][0–9]

00 000

Alarm when date, hours, minutes, seconds, tenths, and

hundredths of seconds match

[0–9][0–9]

10 000

Alarm when day, hours, minutes, seconds, tenths, and

hundredths of seconds match

Table 3. Alarm Mask Bits

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 ... 23 24

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