Looks like the DROs only need A and B channels to operate (/A and /B not used to update DROs).
But, when Reset is clicked, the Mach Ajax Plugin compares at least the A and /A to get a signal level. If that level is below 3V then the error is triggered.
With line driver output encoders this is no problem, however my encoders are SumTak LBL-041-500 5v 160ma open collector outputs.
The Tree325 Dynapath controller did not use the /A, /B or /Z signals and only had 1k pullups on the A, B and Z signals.
The schematic Ajax supplied simply showed to hook up an encoder straight thru with no pullups.
Somehow the DROs updated even without pullups but the High state read only 0.012V and the low was 0.08V.
I attached the 1k pullups and was able to get a High state of 0.88V and a Low of 0.1V.
With 510 ohm pullups I get 1.3V High and 0.2V Low.
The Tree ran for 20 years with no noise problems so I am basically happy using the 510 ohm pullups which gives the MPU11 inputs 7ma in the 1.3V High state.
It looks like the signals go into an AM26LV32, BiCMOS, quadruple, differential line receiver.
The response from Ajax has been very positive and they are willing to provide a Beta version Plugin to me that has a parameter that can be set to turn off the 3V signal check when Reset is clicked.
Does anybody see a problem with this decision? There are a lot of open collector encoders out there as potential upgrades so I hope this is a good way to go.