Jogging and pen/up down from the original control panel works pretty well - but the code still needs a bit of polishing. There are reset in and out signals I have to figure out how to put to work - and the red alert LED should be lit on error conditions such as bad HPGL code received?

Next up is a blanking plate for the big hole left where the serial and parallell ports were, now it will only be a small cutout for the micro USB. And I have to make some pen holders so that automatic pen selection can be verified.