DS2422 Maxim, DS2422 Datasheet - Page 13

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

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/data 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.
Writing a sample rate of 0000h results in a sample rate = 0001h, causing the DS2422 to log either every minute or
every second depending upon the state of the EHSS bit.
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 DS2422 can measure temperatures from -40°C to +85°C. Temperature values are represented as an 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 is indicated as 00h or 0000h when too cold and FFh or FFE0h when too hot.
Latest Temperature Conversion Result Register Bitmap
With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is
calculated as
(°C) = TRH/2 - 41 + TRL/512
(°C) = TRH/2 - 41
This equation is valid for converting temperature readings stored in the datalog memory as well as for data read
from the Latest Temperature Conversion Result Register.
To specify the temperature alarm thresholds, the equation above needs to be resolved to
TALM = 2 *  (°C) + 82
Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C.
The TALM value needs to be converted into hexadecimal format before it can be written to one of the temperature
alarm threshold registers (Low Alarm address 0208h; High Alarm address 0209h). Independent of the
conversion mode (8 or 16 bit) only the most significant byte of a temperature conversion is used to determine
whether an alarm will be generated.
Temperature Conversion Examples
8-bit
8-bit
16-bit
16-bit
020Ch
020Dh
ADDR
0206h
0207h
ADDR
Mode
hex
T10
54h
17h
54h
17h
T2
b7
b7
0
TRH
decimal
T1
T9
b6
b6
84
23
84
23
0
hex
00h
60h
T0
T8
b5
b5
—
—
TRL
decimal
Sample Rate Low
T7
b4
b4
96
—
—
0
0
Sample Rate High
(16 bit mode, TLFS = 1, see address 0213h)
(8 bit mode, TLFS = 0, see address 0213h)
-29.3125
13 of 49
b3
b3
T6
(°C)
0
1.000
-29.5
1.0
b2
b2
T5
0
b1
b1
T4
0
b0
b0
T3
0
TRH
TRL