andy pugh wrote: > On 1 December 2010 17:59, Stephen Wille Padnos<spad...@sover.net> wrote: > >> And to add to the complications, you don't know where you'll get the >> rising edge once the axis has tripped the limit switch. >> > A custom comp could watch the axis.N.home-state pin. Assuming that the > axis is set up for two-stage homing it could then set the index-enable > bit for the encoder counter and homing could be done on an OR of > home-switch state and index-enable (as index-enable will then go low > once the index is seen). > Yes, a .comp could do it as easily as an AVR, if a little slower. I don't think that the index-enable manipulations would help though, since this is (a) not running to an encoder and (b) used in concert with a stepgen. Stepgen has no way of using an encoder index for position reset/latch, which is itself another set of problems. Those issues would be worked around by setting a sufficiently slow search velocity. In the end, it's a matter of making the home switch trip point more accurate than a mechanical switch, while retaining the characteristics needed for a home switch (splitting the axis travel into two regions, not three). > However, I think we are over-complicating this. If the p-port can't > see the index then it can't see the encoder edges and this is all > moot. > I think the original idea was not to use the encoder as a position feedback device. The AB phases would be run to the Gecko drives, and the index would come back to the computer for more accurate homing.
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