NXP Semiconductors MC9S08LG16, Reference Manual

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Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
MC9S08LG32 MCU Series, Rev. 5
Freescale Semiconductor 203
ALTCLK on the MC9S08LG32 series is connected to the ICSERCLK. See Chapter 11, “Internal Clock
Source (S08ICSV3) ,” for more information.
10.1.4.4 Hardware Trigger
The RTC can be enabled as a hardware trigger for the ADC module by setting the ADTRG bit in the
ADCSC2 register. When enabled, the ADC will be triggered every time a RTC overflow condition occurs.
The RTC overflow 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.
10.1.4.5 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 in the MC9S08LG32 Data Sheet .
In application code, you read the temperature sensor channel, calculate V
TEMP
, and compare it 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 .