DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 17

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

TIMEKEEPING AND CALENDAR
The real-time clock (RTC)/alarm and calendar information is accessed by reading/writing the appropriate bytes in
the register page, address 200h to 205h. For readings to be valid, all RTC registers must be read sequentially
starting at address 0200h. Some of the RTC bits are set to 0. These bits will always read 0 regardless of how they
are written. The number representation of the real-time clock registers is BCD format (binary-coded decimal).
Real-Time Clock and RTC Alarm Register Bitmap
The RTC of the DS1922L/T 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). The CENT
bit, bit 7 of the Months Register, can be written by the user. This bit changes its state when the years counter
transitions from 99 to 00.
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 29
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 temperature logging events. The sample rate may be any value from 1 to
16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging events is 1
second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and the longest
time is 273.05 hours ( 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. A
sample rate of 0000h is not valid and must be avoided under all circumstances. This will cause the device
to enter into an unrecoverable state.
Sample Rate Register Bitmap
During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be
written to 1.
TEMPERATURE CONVERSION
The DS1922L measures temperatures in the range of -40°C to +85°C. With the DS1922T the temperature range
begins at 0°C and ends at +125°C. Temperature values are represented as a 8- or 16-bit unsigned binary number
with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.
The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte
TRL are valid. The five lower bits all read zero. TRL is undefined if the device is in 8-bit temperature mode. An out-
of-range temperature reading will be indicated as 00h or 0000h when too cold and FFh or FFE0h when too hot.
ADDR
ADDR
0200h
0201h
0202h
0203h
0204h
0205h
0206h
0207h
CENT
b7
b7
0
0
0
0
0
12/24
b6
b6
0
0
0
10yrs
10min.
AM/PM
20hr
10s
b5
b5
0
10 Date
th
of February. This will work correctly up to (but not including) the year 2100.
Sample Rate Low
10m.
10hr
b4
b4
Sample Rate High
17 of 50
b3
b3
Single Seconds
Single Minutes
Single Months
Single Hours
Single Years
b2
b2
Single Date
b1
b1
b0
b0
DS1922L/DS1922T