DS1921 datasheet(7/44 Pages) DALLAS

7 / 44 page

DS1921H/Z

7 of 44

RTC and RTC Alarm Register Bitmap

ADDR

0200h

10 Seconds

Single Seconds

0201h

10 Minutes

Single Minutes

0202h

12/24

20h.

AM/PM

10h.

Single Hours

0203h

Day of Week

0204h

10 Date

Single Date

0205h

CENT

10m.

Single Months

0206h

10 Years

Single Years

0207h

10 Seconds Alarm

Single Seconds Alarm

0208h

10 Minutes Alarm

Single Minutes Alarm

0209h

12/24

10ha.

A/P

10h.

alm.

Single Hours Alarm

020Ah

Day of Week Alarm

RTC/Calendar

The RTC of the DS1921H/Z can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register

(address 202h) 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 1 being PM. In the 24-hour mode, bit 5 is the 20-

hour bit (20 to 23 hours).

To distinguish between the days of the week the DS1921H/Z includes a counter with a range from 1 to 7.

The assignment of counter value to the day of week is arbitrary. Typically, the number 1 is assigned to a

Sunday (U.S. standard) or to a Monday (European standard).

The calendar logic is designed to automatically compensate for leap years. For every year value that is

either 00 or a multiple of 4 the device will add a 29

th of February. This will work correctly up to (but not

including) the year 2100.

The DS1921H/Z is Y2K-compliant. Bit 7 (CENT) of the Months Register at address 205h serves as a

century flag. When the Year Register rolls over from 99 to 00 the century flag will toggle. It is recom-

mended to write the century bit to a 1 when setting the RTC to a time/date between the years 2000 and

2099.

RTC Alarms

The DS1921H/Z also contains a RTC alarm function. The alarm registers are located in registers 207h to

20Ah. The most significant bit of each of the alarm registers is a mask bit. When all of the mask bits are

logic 0, an alarm will occur once per week when the values stored in timekeeping registers 200h to 203h

match the values stored in the time of day alarm registers. Any alarm will set the Timer Alarm Flag

(TAF) in the device's Status Register (address 214h). The bus master may set the Search Conditions in the

Control Register (address 20Eh) to identify devices with timer alarms by means of the Conditional Search

function (see ROM Function Commands).

DS1921 Datasheet(PDF) 7 Page - Dallas Semiconductor

DS1921 Datasheet(HTML) 7 Page - Dallas Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

Datasheet Descarga

Enlace URL