PXR40RM Datasheet, PDF (1086/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Enhanced Queued Analog-to-Digital Converter (EQADC)
Minimum time necessary to perform a single
conversion after channel number is changed
MUX Settle Time
and Sampling
AD Conversion
Conversion starts immediately after channel #
change.ADC sample time should compensate
for MUX internal capacitance settling and for the
sampling on the sampling capacitor. If sample
time is not long enough, this can lead to
inaccurate conversion results.
MUX Settle Time
and Sampling
AD Conversion
Channel # Change
and Sample Start
Channel # Change
and Sample Start
(a) Command Execution Sequence for Two Non-Overlapped Commands
MUX Settle Time
and Sampling
AD Conversion
MUX Settle Time
Sampling
AD Conversion
Channel # Change
and Sample Start
Change
Channel #
Sample Start
Channel # changes before sampling starts leading to
more time for MUX internal capacitance to settle.
(b) Command Execution Sequence for Two Overlapped Commands
Figure 27-66. Overlapping Consecutive Conversion Commands
27.7.7 Internal/External Multiplexing
27.7.7.1 Channel Assignment
The internal analog multiplexers select one of the 40 analog input pins for conversion, based on the
CHANNEL_NUMBER field of a Command Message. The analog input pin channel number assignments
and the pin definitions vary depending on how the ADC0/1_EMUX are configured. Allowed combinations
of ADC0/1_EMUX bits are shown in Table 27-42 together with references to tables indicating how
CHANNEL_NUMBER field of each conversion command must be set to avoid channel selection
conflicts.In addition to this master multiplexer, each ADC is equipped with a secondary multiplexer that
are used to monitor signals internal to the chip. These analog input pins are also selected by the
CHANNEL_NUMBER field.
27-104
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor