Datasheet

DS1921G
Thermochron iButton
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ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION ACCESS*
0210h (No function, reads 00h) — R R**
0211h Temperature Read-Out (Forced Conversion) Temperature R R**
0212h Low Byte
0213h High Byte
Mission Start
Delay
R/W R/W**
0214h TCB MEMCLR MIP SIP 0 TLF THF TAF Status R/W R/W
0215h Minutes
0216h Hours
0217h Date
0218h Month
0219h Year
Mission
Timestamp
R R
021Ah Low Byte
021Bh Center Byte
021Ch High Byte
Mission
Samples
Counter
R R
021Dh Low Byte
021Eh Center Byte
021Fh High Byte
Device
Samples
Counter
R R
Figure 6. Register Pages Map (continued)
* The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access mode while a
mission is in progress.
** While a mission is in progress, these addresses can be read. The first attempt to write to these registers (even read-only
ones), however, ends the mission and overwrites selected writable registers.
Detailed Register Descriptions
Timekeeping
The RTC/alarm and calendar information is accessed
by reading/writing the appropriate bytes in the register
page, address 0200h to 0206h. Note that some bits are
set to 0. These bits always read 0 regardless of how
they are written. The contents of the time, calendar, and
alarm registers are in the binary-coded decimal (BCD)
format.
RTC/Calendar
The RTC of the DS1921G can run in either 12hr or 24hr
mode. Bit 6 of the Hours register (address 0202h) is
defined as the 12hr or 24hr mode select bit. When high,
the 12hr mode is selected. In the 12hr mode, bit 5 is the
AM/PM bit with logic 1 being PM. In the 24hr mode, bit
5 is the 20hr bit (20hr to 23hr).
To distinguish between the days of the week, the
DS1921G includes a counter with a range from 1 to 7.
The assignment of a 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 stan-
dard).
The calendar logic is designed to automatically com-
pensate for leap years. For every year value that is
either 00 or a multiple of four, the device adds a 29th of
February. This works correctly up to (but not including)
the year 2100.
The DS1921G is Y2K compliant. Bit 7 (CENT) of the
Months register at address 0205h serves as a century
flag. When the Year register rolls over from 99 to 00, the
century flag toggles. It is recommended to write the
century bit to a 1 when setting the RTC to a time/date
between the years 2000 and 2099.