Information

format and the effect will be an addition. An offset correction that results in an out-of-
range value will be forced to the minimum or maximum value (the minimum value for
single-ended conversions is 0x0000; for a differential conversion it is 0x8000).
To preserve accuracy, the calibrated offset value initially stored in the OFS register must
be added to the user defined offset. For applications that may change the offset repeatedly
during operation, it is recommended to store the initial offset calibration value in flash so
it can be recovered and added to any user offset adjustment value and the sum stored in
the OFS register.
31.4.8 Temperature sensor
The ADC module includes a temperature sensor whose output is connected to one of the
ADC analog channel inputs. The following equation provides an approximate transfer
function of the temperature sensor.
m
Figure 31-63. Approximate transfer function of the temperature sensor
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 referred as temperature sensor slope in the device data sheet. It is the hot or cold
voltage versus temperature slope in V/°C.
For temperature calculations, use the V
TEMP25
and temperature sensor slope 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
the preceding equation. If V
TEMP
is less than V
TEMP25
, the hot slope value is applied in
the preceding equation. ADC Electricals table may only specify one temperature sensor
slope value. In that case, the user could use the same slope for the calculation across the
operational temperature range.
For more information on using the temperature sensor, see the application note titled
Temperature Sensor for the HCS08 Microcontroller Family (document AN3031).
Chapter 31 Analog-to-Digital Converter (ADC)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 621