Question for Doddy,

I've scoped the common mode noise and it isn't sufficient to cause a phantom step to be read at the 328p. I think the phantom steps I was detecting that I have 'fixed' by debouncing the read are actually being caused by reflections and/or induced voltage spikes as the differential pair switches. If this is correct placing a termination resistor across the pair as you do for rs485 should help do you concur?

Cheers, Joe