More debugging of the NRI 832

Posted on Feb 6, 2014

I`ve made more headway. The other day I built a 6kHz oscillator using a 555 to produce a clock signal that I could inject into the 832. You can see the trace on the scope, and the oscillator itself pictured below. While running on the new clock, the rest of the machine seems to function properly. It`s hard to verify at 6kHz, the status of the accu

More debugging of the NRI 832
Click here to download the full size of the above Circuit.

mulator changes too fast to see. You can however see the program counter going. That is in the above YouTube video. Some more below the link. The oscillator proper consists of Q2 and Q3. Q1 functions as an amplifier to buffer the output. Q4 is driven by the STOP signal from IC59. When a HLT instruction is executed, or the reset button is depressed, the STOP line goes high, pulling that side of the oscillator to ground stopping it. A fair bit of work thus far has gone to undoing some past modifications that had been made to the circuit. Right now, it`s pretty much in line with the schematic. I think my next step may be to duplicate the schematic circuit on a piece of stripboard and see if it behaves. I`m suspicious that C1 is dead. That would definitely kill the oscillator. My attempts at simulating the oscillator on my iPad in iCircuit have been less helpful than hoped. The oscillator seems to run at 128Hz no matter what I change. That is thoroughly wonky. I will try doing it in LTSpice and see if it behaves better.

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