Troubleshooting bench testing setup for the 1627 controller card

COMPLEX BENCH TESTING SETUP NOT WORKING PROPERLY

The setup makes use of a breadboard development system, an Arduino Uno, several power supplies, an oscilloscope and my SLT breakout box. The breadboard development system includes both 5V and adjustable power rails, plenty of breadboard space, two debounced pushbuttons, display LEDs and various types of switches. External 9V, 12V and -24V supplies round out the setup; the 9V supply powers the Arduino. 

The breadboard has open collector buffers to convert the 5V signals of the Arduino to 3V consistent with SLT logic. I didn't have any hex buffers in DIP format, so I had to wire up pairs of hex inverter chips to produce the same outcome, using pull-ups to 3V on the chips. I also used a pair of debounced pushbuttons to trigger behaviors in the Arduino. 

NOT SEEING REACTION TO WRITING TO THE PLOTTER

I watched the scope expecting to see the command lines to the plotter dip down as well as the interrupt request line go active, but there was no activity. I started debugging to see that I was properly sending the signals needed by my card - XIO Write, Area 5, T6, plus one of the B register bits. I saw T6 triggering but not Area 5 nor XIO Write. 

It was a rooky mistake. I had started serial communications just to get a bit of debugging information, but that uses pins 0 and 1 for the serial link. I had assigned those to the two missing signals. Removing the serial activity frees up pin 1, but pin 0 isn't useful on the Arduino Uno. With the removal of serial activity, I did see Area 5 going active. 

I moved the XIO Write wire to pin 12 and changed my Arduino code, but it did not activate. I even checked the wire for continuity and put that wire directly to a scope lead without any connection to the breadboard - still no sign of life. 

The Arduino I used was an old one I pulled out of a parts bin - one that had been used for prior projects. Just in case there is something wrong with it, I ordered a new Uno which I can swap in. Until I can pulse the XIO Write line, the board will not do anything meaningful.