All chips installed and some testing on EDUC-8 while I wait on connectors and switches

LAST CHIPS ARRIVED AND WERE INSTALLED ON THE BOARDS

The boards are waiting on the decoupling 47nf capacitors otherwise all components are installed other than connectors and switches. The connectors, cables and switches are coming from China as I bought them on AliExpress. The estimates for arrival are June 14, June 17, June 20 and July 1 for various items in the order. 

INITIAL TESTING OF FRONT PANEL AND TIMING BOARD

I was able to test all the LED driver circuits on the front panel, switching them on or off by grounding the input pins on the edge connectors. Most of the switch circuits are not debounced thus there is almost nothing to them. I verified that, once the switch is installed and operates properly, the outputs are changing appropriately. 

A few of the switches are debounced, using this type of circuit:

Two one-shot gates are used to convert certain switches to a single short pulse per activation, using a circuit like this:


I didn't test this either. It is possible that I could go back and test using jumpers or even wiring in a temporary switch, otherwise I will wait until the final parts arrive. 

The timing board produces the main oscillator and then steps through 24 cycles, the first half for the Fetch stage of instruction processing and the second half for the Execute stage. It creates the power on reset signal as well. There are some run and halt controls which either pass the clock pulses or block them from the rest of the circuitry.

The board then emits signals for particular steps of the 24 cycles. Some are only emitted for certain instructions or function states, others are always produced. 

I saw the reset circuit working properly, the main clock producing good clean oscillations, and the system starting out with all the other output signals blocked as the machine starts in a halted state. By triggering the Run Command condition, I turned on the run state and checked that all the pulse outputs were being produced. 

I did not control the conditional inputs such as IOT instruction or DEP+EXAM state, letting the output pulses show on the output pins. I also didn't fully model the various Run and Halt inputs. Finally, the output pulses were observed but I did not watch them in the context of the full 24 cycles to ensure they are at the correct time and intended duration.  

I only wanted to see that it was plausibly working as it should. At a later time I may do a more extensive test to check it out fully.

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