MC9S08DZ60 Datasheet, PDF (169/396 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 10 Analog-to-Digital Converter (S08ADCV1)
The period of the RTC is determined by the input clock frequency, the RTCPS bits, and the RTCMOD
register. When the ADC hardware trigger is enabled, a conversion is initiated upon an RTC counter
overflow.
The RTC can be configured to cause a hardware trigger in MCU run, wait, and stop3.
10.1.5 Temperature Sensor
To use the on-chip temperature sensor, the user must perform the following:
• Configure ADC for long sample with a maximum of 1 MHz clock
• Convert the bandgap voltage reference channel (AD27)
— By converting the digital value of the bandgap voltage reference channel using the value of
V_BG the user can determine V_DD. For value of bandgap voltage, see Section A.6, “DC
Characteristics”.
• Convert the temperature sensor channel (AD26)
— By using the calculated value of V_DD, convert the digital value of AD26 into a voltage, V_TEMP
Equation 10-1 provides an approximate transfer function of the on-chip temperature sensor for V_DD =
3.0V, Temp = 25°C, using the ADC1 at f_ADCK = 1.0MHz and configured for long sample.
Temp_C = 25 - ( (V_TEMP - 0.7013) / 0.0017 )
Eqn. 10-1
0.0017 is the uncalibrated voltage versus temperature slope in V/°C. Uncalibrated accuracy of the
temperature sensor is approximately ± 12°C, using Equation 10-1.
To improve accuracy the user should calibrate the bandgap voltage reference and temperature sensor.
Calibrating at 25°C will improve accuracy to ± 4.5°C.
Calibration at three 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.
MC9S08DZ60 Series Data Sheet, Rev. 1 Draft E
Freescale Semiconductor
PRELIMINARY
169
Subject to Change