S9S12G128F0CLF Datasheet, PDF (437/1158 Pages) Freescale Semiconductor, Inc – MC9S12G Family Reference Manual

Analog-to-Digital Converter (ADC10B16CV2)
Table 13-22 shows how depending on the A/D resolution the conversion result is transferred to the ATD
result registers for right justified data. Compare is always done using all 12 bits of both the conversion
result and the compare value in ATDDRn.
Table 13-22. Conversion result mapping to ATDDRn
A/D
resolution
DJM
conversion result mapping to ATDDRn
8-bit data 1
Result-Bit[7:0] = result,
Result-Bit[11:8]=0000
10-bit data 1
Result-Bit[9:0] = result,
Result-Bit[11:10]=00
13.4 Functional Description
The ADC10B16C consists of an analog sub-block and a digital sub-block.
13.4.1 Analog Sub-Block
The analog sub-block contains all analog electronics required to perform a single conversion. Separate
power supplies VDDA and VSSA allow to isolate noise of other MCU circuitry from the analog sub-block.
13.4.1.1 Sample and Hold Machine
The Sample and Hold Machine controls the storage and charge of the sample capacitor to the voltage level
of the analog signal at the selected ADC input channel.
During the sample process the analog input connects directly to the storage node.
The input analog signals are unipolar and must be within the potential range of VSSA to VDDA.
During the hold process the analog input is disconnected from the storage node.
13.4.1.2 Analog Input Multiplexer
The analog input multiplexer connects one of the 8 external analog input channels to the sample and hold
machine.
13.4.1.3 Analog-to-Digital (A/D) Machine
The A/D Machine performs analog to digital conversions. The resolution is program selectable to be either
8 or 10 bits. The A/D machine uses a successive approximation architecture. It functions by comparing the
sampled and stored analog voltage with a series of binary coded discrete voltages.
By following a binary search algorithm, the A/D machine identifies the discrete voltage that is nearest to
the sampled and stored voltage.
When not converting the A/D machine is automatically powered down.
MC9S12G Family Reference Manual, Rev.1.10
Freescale Semiconductor
437