67.6.16.7 Detecting a Badly Located Index

The digital filter reduces effects of dust, scratches or contamination on the index line. If the contamination creates a pulse surpassing the filter capacity (in particular at low speed), this can be interpreted as an index pulse, even if it is badly placed.

An on-the-fly detection of a badly-placed index is enabled when TC_BMR.BIDXCE=1. TC_RC0.RC must be written with the nominal number of counts per revolution provided by the rotary encoder + 2. For example, if the nominal count per revolution is 1024, then TC_RC0.RC=1026. This margin of 2 eliminates potential noise.

If the pulse is processed while the current value of the counter (TC_CV0) is outside the value programmed in TC_RC0.RC ±2, the TC_SR0.LDRAS flag is written to ‘1’ and the location of the pulse is written in TC_RA0.

This detection circuitry does not prevent a rotary encoder integrity check before use.