MC9S08JM60_09 Datasheet, PDF (137/388 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
ADCSC2[ADTRG] bit. When enabled, the ADC will be triggered every time RTCINT matches
RTCMOD. The RTC interrupt does not have to be enabled to trigger the ADC.
The RTC can be configured to cause a hardware trigger in MCU run, wait, and stop3.
10.1.1.4 Analog Pin Enables
The ADC on MC9S08JM60 series contains only two analog pin enable registers, APCTL1 and APCTL2.
10.1.1.5 Temperature Sensor
The ADC module includes a temperature sensor whose output is connected to one of the ADC analog
channel inputs. Equation 10-1 provides an approximate transfer function of the temperature sensor.
Temp = 25 – ((V_TEMP – V_TEMP25) ÷ m)
Eqn. 10-1
where:
— V_TEMP is the voltage of the temperature sensor channel at the ambient temperature.
— 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 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 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. 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 10-1 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.
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.
MC9S08JM60 Series Data Sheet, Rev. 3
Freescale Semiconductor
137