CV Read always returns a value of 255

[richd286]

When I read any CV on the service track I get a value of 255.   I have programmed different values in various CVs and can see the expected effect in engine performance so I believe the CV values are changing.  Does anyone have experience with this CV read problem.  I have a ProBox wired correctly.  Thanks.

[Hunt]

What decoder is in your engine?

[WoundedBear]

Some decoders don't support "read back".

Sid