Unexpected results from Encoder::GetRate()

[jhersh]

Originally Posted by vamfun

Joe, I would expect that for 2x and 4x but not 1x, since with 1x only A channel leading edge determines the count and the B channel is always the same value on the leading edge. Unless I'm missing something.

Originally Posted by vamfun

Ok, lets get specific. When we write our own interrupt encoder routines, the B channel is just looked at when a TEU pulse occurs on the A chan to get the direction. However, the tcounters in CRIO are a bit of a mystery to me still and I need some more tutoring.

I think the fundamental misunderstanding here is that what you are doing in your microcontroller-based 1x decoder is take a shortcut that is not a valid quadrature decoder.

To create a valid 1x decoder, you must be sensitive to a different edge of A based on the value of B, not always be sensitive to one edge of A and choose direction based on B. Naturally the correct way to implement this is not simple on a microcontroller because interrupt configuration cannot be tied to a digital input, so the mistake is often made because it is seen as the only option. The fact that it almost works only reinforces to the misunderstanding.

In some cases is it a concious decision to use this optimization (which has half the interrupt traffic that would be required to implement it correctly) with the acceptance and acknowledgement that it will generate invalid counts any time the direction changes.

-Joe