PXS20RM Datasheet, PDF (210/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Analog-to-Digital Converter (ADC)
9.4.11.7 Baud rate control for test channel
This control defines the scheduling of test channel between the normal conversions. The scheduling rate
is specified by STBRR[BR].
By default, if test channel is enabled, one Step of selected algorithm is executed after every chain of normal
conversion. The bandwidth consumed by test channel depends on the number of channels in normal chain.
e.g. if we have 100 normal conversions in a chain, then test channel consumes only 1% of total bandwidth,
which is very small. But in case the number decreases to just 4 channels, then the bandwidth consumed by
test channel is 25%, which is significant (and may not be desirable as it slows down the normal conversion
rate).
STBRR[BR] field provides flexibility by scheduling the test channel conversion to be performed not at the
end of every chain but at the end of BR+1 number of chains. e.g. if BR = 5, a single Step of selected
Algorithm for test channel is performed after 6 chain conversions, then next Step is performed at end of
next 6 chain conversions and so on. By default, the value of BR is 0.
To use the baud rate feature in scan mode, the NCMR should have a non-zero value.
NOTE
This feature is applicable only for scan mode of operation and not for one
shot mode. The STBRR.BR should be set to zero for one shot mode.
9.4.11.7.1 Abort chain when baud rate is non-zero
As already described, for non-zero value of STBRR[BR] field, the test channel conversion is performed
at the end of (BR+1) number of chains. If abort chain occurs during the chain in which test channel is
scheduled to be converted, then test channel is converted after next (BR+1) number of chains.
For example, if STBRR.BR field is programmed to 2, the sequence will be two normal chains (without
any test channel conversion) followed by chain with test channel converted at the end. Now, if abort chain
occurs during first two chains it is treated as normal chain abort and test channel is converted at the end of
3rd chain only (as the case without any abort chain). But if abort chain occurs during the 3rd chain in which
test channel is scheduled to be converted, then test channel is converted after next three chains — that is,
at the end of 6th chain (counting from the beginning).
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PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor