SPRUHX5I August 2014 – May 2024 TMS320F28374S , TMS320F28375S , TMS320F28375S-Q1 , TMS320F28376S , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28378S , TMS320F28379S
The digital filter works on a window of FIFO samples (SAMPWIN) taken from the input. The filter output resolves to the majority value of the sample window, where majority is defined by the threshold (THRESH) value. If the majority threshold is not satisfied, the filter output remains unchanged.
For proper operation, the value of THRESH must be greater than SAMPWIN / 2 and less than or equal to SAMPWIN.
A prescale function (CLKPRESCALE) determines the filter sampling rate, where the filter FIFO captures one sample every prescale system clocks. Old data from the FIFO is discarded.
Note that for SAMPWIN, THRESH and CLKPRESCALE, the internal number used by the digital filter is + 1 in all cases. In essence, samples = SAMPWIN + 1, threshold = THRESH + 1 and prescale = CLKPRESCALE + 1.
A conceptual model of the digital filter is shown in Figure 12-6.
Equivalent C code of the filter implementation is:
if (FILTER_OUTPUT == 0) {
if (Num_1s_in_SAMPWIN >= THRESH) {
FILTER_OUTPUT = 1;
}
}
else {
if (Num_0s_in_SAMPWIN >= THRESH) {
FILTER_OUTPUT = 0;
}
}