DS1922T Maxim, DS1922T Datasheet - Page 50

• Manufacturer Part Number: DS1922T
• Description: The DS1922L/T temperature logger iButtons® are rugged, self-sufficient systems that measure temperature and record the result in a protected memory section
• Manufacturer: Maxim

Temperature Logger iButton with 8KB
Data-Log Memory
The accuracy of high-resolution temperature conver-
sion results (forced conversion as well as temperature
logs) can be improved through a correction algorithm.
The data needed for this software correction is stored
in the calibration memory (memory page 18, duplicated
in page 19). This data consists of reference tempera-
ture (T
peratures. See the Temperature Conversion section for
the binary number format.
The software correction algorithm requires two addi-
tional values, which are not stored in the device. These
values, Tr1 and Offset, are derived from the device
configuration byte.
Step 1. Preparation
Read the 64-bit ROM to obtain the family code. If family code ≠ 41h, then stop (wrong device).
Read the configuration byte at address 0226h.
If code = 40h, then Tr1 = 60, Offset = 41 (DS1922L)
If code = 60h, then Tr1 = 90, Offset = 1 (DS1922T)
For all other codes, stop (wrong device).
Tr2 = Tr2H/2 + Tr2L/512 - Offset (convert from binary to °C)
Tr3 = Tr3H/2 + Tr3L/512 - Offset (convert from binary to °C)
Tc2 = Tc2H/2 + Tc2L/512 - Offset (convert from binary to °C)
Tc3 = Tc3H/2 + Tc3L/512 - Offset (convert from binary to °C)
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr2
A = B x (Tr1 - Tr2) / (Tr2
C = Err1 - A x Tr1
Step 2. Execution
T
T
50
C
CORR
= TcH/2 + TcL/512 - Offset (convert from binary to °C)
______________________________________________________________________________________
r
Software Correction Algorithm
) and conversion result (T
= Tc - (A x Tc
2
ADDRESS
- Tr1
0240h
0241h
0242h
0243h
0244h
0245h
0246h
0247h
2
) x (Err3 - Err1)/[(Tr2
2
- B x Tr1
2
+ B x Tc + C) (the actual correction)
2
- Tr1
for Temperature
2
)
c
) for two different tem-
DESIGNATOR
2
- Tr1
Tc2H
Tc3H
Tc2L
Tc3L
Tr2H
Tr3H
Tr2L
Tr3L
2
) x (Tr3 - Tr1) + (Tr3
Cold-reference temperature, high byte
Cold-reference temperature, low byte
Conversion result at cold-reference temperature, high byte
Conversion result at cold-reference temperature, low byte
Hot-reference temperature, high byte
Hot-reference temperature, low byte
Conversion result at hot-reference temperature, high byte
Conversion result at hot-reference temperature, low byte
The correction algorithm consists of two steps: prepa-
ration and execution. By means of the family code the
preparation step verifies whether the device actually is
a DS1922. Then the configuration byte is checked to
identify the type of DS1922 (L or T). If it is the correct
device, the data for software correction is read and
converted from binary to decimal °C format. Next,
three coefficients A, B, and C are computed. In the
execution step, the temperature reading as delivered
by the DS1922 is first converted from the low-
byte/high-byte format (TcL, TcH) to °C (T
corrected to T
three coefficients can be used repeatedly to correct
any temperature reading and temperature log of the
same device .
2
- Tr1
2
) x (Tr1 - Tr2)]
CORR
DESCRIPTION
. Once step 1 is performed, the
c
) and then