DS1921G-F5 Ver la hoja de datos (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS1921G-F5

Thermochron iButton

Dallas Semiconductor -> Maxim Integrated 

RTC and RTC Alarm Register Bitmap

DS1921G Thermochron iButton

ADDR b7

0200h

0

0201h

0

0202h

0

0203h

0204h

0205h

0206h

0207h

0208h

0209h

0

0

CENT

MS

MM

MH

020Ah MD

b6

b5

b4

10 Seconds

10 Minutes

12/24 20h. 10h.

AM/PM

0

0

0

0

10 Date

0

0

10m.

10 Years

10 Seconds Alarm

10 Minutes Alarm

12/24 10ha. 10h.

A/P alm.

0

0

0

b3

b2

b1

b0

Single Seconds

Single Minutes

Single Hours

0

Day of Week

Single Date

Single Months

Single Years

Single Seconds Alarm

Single Minutes Alarm

Single Hours Alarm

0

Day of Week Alarm

RTC/Calendar

The RTC of the DS1921G 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 DS1921G 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 29th of February. This will work correctly up to (but not

including) the year 2100.

The DS1921G 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 DS1921G 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).

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