Datasheet

DS1921G
RTC Alarms
The DS1921G also contains an RTC alarm function. The
RTC Alarm registers are located in registers 0207h to
020Ah. The most significant bit of each of the alarm
registers is a mask bit. When all the mask bits are logic
0, an alarm occurs once per week when the values
stored in timekeeping registers 0200h to 0203h match
the values stored in the RTC Alarm registers. Any alarm
sets the timer alarm flag (TAF) in the device’s Status
register (address 214h). The bus master can set the
search conditions in the Control register (address
20Eh) to identify devices with timer alarms by means of
the conditional search function (see the ROM Function
Commands section).
Thermochron iButton
12 ______________________________________________________________________________________
RTC Alarm Control
ALARM REGISTER MASK BITS
(BIT 7 OF 0207h TO 20Ah)
MS MM MH MD
FUNCTION
1 1 1 1 Alarm once per second.
0 1 1 1 Alarm when seconds match (once per minute).
0 0 1 1 Alarm when minutes and seconds match (once every hour).
0 0 0 1 Alarm when hours, minutes, and seconds match (once every day).
0 0 0 0 Alarm when day, hours, minutes, and seconds match (once every week).
RTC and RTC Alarm Registers Map
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0200h 0 10 Seconds Single Seconds
0201h 0 10 Minutes Single Minutes
0202h 0 12/24
20 Hour
AM/PM
10 Hour Single Hours
0203h 0 0 0 0 0 Day of Week
0204h 0 0 10 Date Single Date
0205h CENT 0 0 10 Months Single Months
0206h 10 Years Single Years
0207h MS 10 Seconds Alarm Single Seconds Alarm
0208h MM 10 Minutes Alarm Single Minutes Alarm
0209h MH 12/24
20 Hour
AM/PM
Alarm
10 Hour
Alarm
Single Hours Alarm
020Ah MD 0 0 0 0 Day of Week Alarm