I'm thinking it may be signal voltage. This tech note lists the the high must be greater than 3.5V.
http://www.centroidcnc.com/dealersup...ploads/280.pdf
1. Confirm that you encoders meet Centroid signal specifications. Centroid requires
quadrature, differential line driver encoders that meet the RS422/423 specifications.
In
addition, the “low” signal level must be < .5VDC and the “high” must be >= 3.5VDC.
The spec sheet from Omron lists the Vo: 2.5 V min. and Vs: 0.5 V max. This matches the spec sheet for the TI RS422 differential driver chip used on this clone. I don't recall what the voltage was when we had it on the scope.
I wonder what Centroid is thinking. A real RS422 receiver shouldn't care what the voltages are, only the difference between the lines. That is the whole point of using differential signals.
I guess I need to find an encoder that meets Centroid specifications.