C8051T620/1/6/7 & C8051T320/1/2/3
58
Rev. 1.2
9.1. Calibration
The uncalibrated temperature sensor output is extremely linear and suitable for relative temperature mea-
surements (see Table 7.11 on page 41 for specifications). For absolute temperature measurements, offset
and/or gain calibration is recommended.
A single-point offset measurement of the temperature sensor is performed on each device during produc-
tion test. The TOFFH and TOFFL calibration values represent the output of the ADC when reading the
temperature sensor at 0 degrees Celsius, and using the internal regulator as a voltage reference. The
TOFFH and TOFFL values can be read from EPROM memory and are located at 0x3FFB (TOFFH) and
0x3FFA (TOFFL). The temperature sensor offset information is left-justified, so TOFFH contains the 8
most-significant bits of the calibration value and TOFFL.7-6 contain the 2 least-significant bits of the cali-
bration value, as shown in Figure 9.2. One LSB of this measurement is equivalent to one LSB of the ADC
output under the measurement conditions.
Figure 9.2. TOFFH and TOFFL Calibration Value Orientation
Figure 9.3 shows the typical temperature sensor error assuming a 1-point calibration at 0 °C.
Parameters
that affect ADC measurement, in particular the voltage reference value, will also affect temperature
measurement.
Figure 9.3. Temperature Sensor Error with 1-Point Calibration at 0 Celsius
TOFFH
TOFFL
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
10-bit Temperature Sensor Offset Calibration Value
-40.00
-20.00
0.00
20.00
40.00
60.00
80.00
Temperature (degrees C)
E
rr
o
r (d
egr
e
es C
)
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
