Probably because he is not using a G540, that was my typo, its G203's he has.

Hood

So the definitive answer was that Mach has a configuration switch that turns on/off the charge pump during an e-stop.  The PMDX-126 uses absence, then presence of the charge pump waveform to infer the reset condition.  So I guess this is a newbie error...once I changed the configuration to "no charge pump during e-stop" it works as one would expect!

Thanks to all that helped...Steve in particular!

Joe