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BiSS C mode encoder changing between Absolute and Relative on reset.
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(11-16-2018, 04:53 PM)pilotchute Wrote: We are using a Renishaw Resolute BiSS-C 26 bit encoder to determine the absolute rotational angle of a telescope aperture wheel.

The following issue has become the last bug in our system.

Upon boot or a reset, the encoder may correctly relay the absolute position, or may show the relative position from where it was at the time of the boot or reset...

My first guess would be that the absolute position read on power-cycle/reset is occurring before the encoder registers within the ACC84x have been 'filled' by a completed read from the encoder.

<edit - I'm more familiar with the Turbo than Power architecture, so take the above with a grain of salt.>

The 'absolute home' position transferred into the motor[4].<structure> might == 0 in that case. Moves from that point would be the relative moves you're observing.

I expect that waiting a few cycles after startup to perform the absolute home read would fix this. Also, try checking the error bits up in the upper byte before allowing an absolute home; I'd think that the bits that should be '1' would also be zero in your startup condition.

(BTW, we're in a similar position in handling encoder errors or loss, albeit dual Renishaw BiSS-C encoders over MACRO, so we'll need to push the error bits over MACRO I/O, after initializing and handling ring errors, etc.)
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RE: BiSS C mode encoder changing between Absolute and Relative on reset. - BCSB_motion - 11-17-2018, 05:43 PM

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