Finished breadboard testing of 5806223 card replacement for controlling 1627 plotter on IBM 1130

VALIDATED THE PLOTTER READY CIRCUIT

The plotter interface has a -24V line that is sensed to determine if the plotter is connected and turned on. This is connected in a resistor voltage divider with +12V on the other end, producing either +12V or a negative voltage when the plotter is ready. 

I tested the output of my added circuitry which should be delivering safe voltages within the range of a TTL input gate - that is no more than 5V and within the voltage requirements of no more than .8 for low and no less then 2 for high. 

This worked properly in simulation, then checked out fine with twin power supplies and the same circuit on the breadboard. 

VALIDATED THE BEHAVIOR OF FLIPFLOPS AND RESET FOR COMMANDS

Each of the six plotter commands (move left, move right, paper up, paper down, pen up and pen down) set a flipflop to drive the 1627 which should be reset after the proper duration (1.9ms except then pen commands are 50ms).

I found that it wasn't resetting at the point I wanted, but when I made a change everything worked exactly as I desired. Schematic and PCB changed to implement this. 

VALIDATED THE BEHAVIOR OF RESPONSE FLIPFLOP AND INTERRUPT REQUEST

As soon as one of the interval timers goes active for a command, the busy line should go on which turns on the operation response flipflop. That drives the inverted request line for an interrupt on level 3. The flipflop is turned off by a Sense DSW with bit 15 of the B register set to 1. 

This all performed as intended, no changes needed. 

VALIDATED THE BEHAVIOR OF SENSE DSW OPERATIONS

A Sense DSW to our device (area code 5) should gate three status signals out to the IO bus, but leave it undisturbed otherwise. The signals are operation response, timer busy and plotter not ready. 

I installed the same chips and connections onto the breadboard and verified that this works as desired. 

LOCKED IN DESIGN AND SENT PCB OUT TO JLCPCB FOR MANUFACTURE

With this working properly to the best of my ability to test it without the actual 1130 system and 1627 plotter, I committed the design and uploaded it to JLCPCB where it will be fabricated. 

FINALIZED PARTS LIST AND ORDERED ON DIGIKEY

With a final design, I adjusted the cart I had set up in Digikey and ordered a set of components required to build one board.