DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 49

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

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
If code = 60h then Tr1 = 90, Offset = 1
For all other codes stop (wrong device)
Tr2 = Tr2H/2 + Tr2L/512 - Offset
Tr3 = Tr3H/2 + Tr3L/512 - Offset
Tc2 = Tc2H/2 + Tc2L/512 - Offset
Tc3 = Tc3H/2 + Tc3L/512 - Offset
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr2
A = B * (Tr1 – Tr2) / (Tr2
C = Err1 - A * Tr1
STEP 2, EXECUTION
Tc = TcH/2 + TcL/512 - Offset
Tcorr = Tc - (A * Tc
Numerical Correction Example
NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for
microcontrollers are found on various websites and are included in cross-compilers.
Converted data from Calibration Memory
Tr1 = 60°C
Tr2 = -10.1297°C
Tr3 = 24.6483°C
Tc2 = -10.0625°C
Tc3 = 24.5°C
Resulting Correction Coefficients
B = -0.008741
A = 0.000175/°C
C = -0.039332°C
2
- Tr1
2
) * (Err3 - Err1)/[(Tr2
2
- B * Tr1
2
+ B * Tc + C)
2
- Tr1
2
)
2
- Tr1
2
) * (Tr3 - Tr1) + (Tr3
Application of Correction Coefficients to sample reading
Tc = 22.500°C
Tcorr = 22.647°C
(DS1922L)
(DS1922T)
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(convert from binary to °C)
(the actual correction)
49 of 50
Error values
Err2 = 0.0672°C
Err3 = -0.1483°C
Err1 = 0.0672°C
2
- Tr1
2
) * (Tr1 - Tr2)]
DS1922L/DS1922T