Datasheet

DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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Detailed Register Descriptions
Timekeeping and Calendar
The RTC and calendar information is accessed by
reading/writing the appropriate bytes in the register
page, address 0200h to 0205h. For readings to be
valid, all RTC registers must be read sequentially start-
ing at address 0200h. Some of the RTC bits are set to
0. These bits always read 0 regardless of how they are
written. The number representation of the RTC registers
is binary-coded decimal (BCD) format.
The DS1922L/DS1922T’s RTC 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). The CENT bit,
bit 7 of the Months register, can be written by the user.
This bit changes its state when the years counter transi-
tions from 99 to 00.
The calendar logic is designed to automatically com-
pensate for leap years. For every year value that is
either 00 or a multiple of 4, the device adds a 29th of
February. This works correctly up to (but not including)
the year 2100.
Sample Rate
The content of the Sample Rate register (addresses
0206h, 0207h) specifies the time elapse (in seconds if
EHSS = 1, or minutes if EHSS = 0) between two tem-
perature-logging events. The sample rate can be any
value from 1 to 16,383, coded as an unsigned 14-bit
binary number. If EHSS = 1, the shortest time between
logging events is 1s and the longest (sample rate =
3FFFh) is 4.55hr. If EHSS = 0, the shortest is 1min and
the longest time is 273.05hr (sample rate = 3FFFh). The
EHSS bit is located in the RTC Control register at
address 0212h. It is important that the user sets the
EHSS bit accordingly while setting the Sample Rate
register. Writing a sample rate of 0000h results in a
sample rate = 0001h, causing the DS1922L/DS1922T
to log the temperature either every minute or every
second depending upon the state of the EHSS bit.
Sample Rate Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0206h Sample Rate Low
0207h 0 0 Sample Rate High
RTC Registers Bitmap
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 10 Date Single Date
0204h CENT 0 0 10 Months Single Months
0205h 10 Years Single Years
Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.
Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.