Datasheet

Chapter 9 Analog-to-Digital Converter (S08ADCV1)
MC9S08SG8 MCU Series Data Sheet, Rev. 8
Freescale Semiconductor 121
For temperature calculations, use the V
TEMP25
and m values from the ADC Electricals table.
In application code, the user reads the temperature sensor channel, calculates V
TEMP
, and compares to
V
TEMP25
. If V
TEMP
is greater than V
TEMP25
, the cold slope value is applied in Equation 9-1. If V
TEMP
is
less than V
TEMP25
, the hot slope value is applied in Equation 9-1. To improve accuracy , calibrate the
bandgap voltage reference and temperature sensor.
Calibrating at 25C will improve accuracy to  4.5C.
Calibration at 3 points, -40C, 25C, and 125C will improve accuracy to  2.5C. Once calibration has
been completed, the user will need to calculate the slope for both hot and cold. In application code, the
user would then calculate the temperature using Equation 9-1 as detailed above and then determine if the
temperature is above or below 25C. Once determined if the temperature is above or below 25C, the user
can recalculate the temperature using the hot or cold slope value obtained during calibration.
Figure 9-1 shows the MC9S08SG8 block diagram with the ADC module highlighted.