It has been suggested on the RepRap forum that I may have corrupted the EEPROM which certainly seems likely, that was the only thing which I had messed with before the trouble began.
The reply post simply said "ā¦ Run the 'clear eeprom' sketch in the arduino tools ... " , but I'm unable to find that in the Tools and it appears from Googling that it's not too tough to brick an Arduino if the method used to clear the EEPROM is incorrect.
Any tips on this?
Enough with the Arduino 8-bit stuff and Marlin, hard to wait until the machine running the Duet is finished.