Thermochron iButton
ADDRESS
0210h
0211h
0212h
0213h
0214h
0215h
0216h
0217h
0218h
0219h
021Ah
021Bh
021Ch
021Dh
021Eh
021Fh
BIT 7
TCB
BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1
(No function, reads 00h)
Temperature Read-Out (Forced Conversion)
Low Byte
High Byte
MEMCLR MIP
SIP
0
TLF
THF
Minutes
Hours
Date
Month
Year
Low Byte
Center Byte
High Byte
Low Byte
Center Byte
High Byte
BIT 0
TAF
FUNCTION
—
Temperature
Mission Start
Delay
Status
ACCESS*
R
R**
R
R**
R/W R/W**
R/W R/W
Mission
Timestamp
R
R
Mission
Samples
R
R
Counter
Device
Samples
R
R
Counter
*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.
Figure 6. Register Pages Map (continued)
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.
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