TC1784
Fast Analog to Digital Converter (FADC)
User´s Manual
24-17
V1.1, 2011-05
FADC, V2.21
•
The moving average length is controlled by FCRn.MAVL defining how many
intermediate results are taken into account for a moving average to build the final
result (final result cycle).
Intermediate Result Calculation
Each incoming conversion result is added to the content of CRRn until the programmed
number of conversion results have been summed up in CRRn. At that point, CRRn
contains a new intermediate result and the calculation of the next final result value by
moving average is started. Then CRRn is cleared automatically after the final result cycle
to be prepared for the first conversion result for the next intermediate cycle.
Before the filter operation of continuous conversion results of channel x is started, the
filter block n has to be cleared (writing GCR.RSTFn = 1) after programming the filter
control bit fields.
Final Result Calculation
The calculation of a final result is started when an intermediate cycle has been finished.
The new intermediate result (stored in CRRn) and the contents of the intermediate
registers IRRnx are added to build the final result in FRRn. The number of intermediate
results taking part in the moving average operation to build the final result is
programmable, the maximum is given by:
•
Filter block 0: FRR0 := CRR0 + IRR10 + IRR20 + IRR30
•
Filter block 1: FRR1 := CRR1 + IRR11
•
Filter block 2: FRR2 := CRR2 + IRR12 + IRR22 + IRR32
•
Filter block 3: FRR3 := CRR3 + IRR13
At the end of the final result cycle, the contents of IRR2n are transferred into IRR3n, then
the contents of IRR1n into IRR2n, then the contents of CRRn into IRR10 (for filter blocks
0 and 2). The former contents of IRR3n are lost.
Bit field FCRn.MAVL determines the number of intermediate results that are used for the
final result calculation. For filter blocks 1 and 3, only two bit combinations are valid and
the intermediate result registers IRR2n and 3n are not available and handled as if they
were 0.
Each update of a result register FRRn with a new final result value generates a filter
block n service request.
24.2.7.3 Filter Concatenation
Filter block 1 and 3 allow filter concatenation to support more filter stages. Filter 1 can
be programmed to use the result value of filter 0, similar for filter blocks 2 and 3.
Filter blocks 0 and 2 operate with the following parameters:
•
Intermediate results are calculated based on the conversion results of one of the
input channels (FCRn.INSEL = 1XX
B
).
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