MC9S08JM16 Datasheet, PDF (135/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
— V_TEMP25 is the voltage of the temperature sensor channel at 25°C.
— m is the hot or cold voltage versus temperature slope in V/°C.
For temperature calculations, use the V_TEMP25 and m values from the Appendix A.9, “ADC
Characteristics.”
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 10-1. If V_TEMP is
less than V_TEMP25, the hot slope value is applied in Equation 10-1.
To improve accuracy, calibrate the bandgap voltage reference and temperature sensor. Calibrating at 25°C
will improve accuracy to ±4.5°C. Calibrating at 3 points, –40°C, 25°C, and 125°C will improve accuracy
to ±2.5°C. Once calibration has been completed, the user needs to calculate the slope for both hot and cold.
In application code, the user would then calculate the temperature using Equation 10-1 as detailed above
and then determine if the temperature is above or below 25°C. Once determined, the user can recalculate
the temperature using the hot or cold slope value obtained during calibration.
10.1.2 Low-Power Mode Operation
The ADC is capable of running in stop3 mode but requires LVDSE and LVDE in SPMSC1 to be set.
MC9S08JM16 Series Data Sheet, Rev. 2
Freescale Semiconductor
135