Nonfunctional Gigatron.

Information about getting support on Gigatron builds
at67
Posts: 433
Joined: 14 May 2018, 08:29

Re: Nonfunctional Gigatron.

Post by at67 »

Dodgy Arduino HW/SW CRO's can be super misleading on digital circuits in the MHz range, they are usually fine for Audio and KHz, but I wouldn't trust what you are displaying.

e.g. Are the units per division correct? If they are then those signals are rubbish, also the signal with ringing/undersampling, (the one you labelled as a better signal), would be breaking TTL noise immunities with a waveform like that. But I would guess that's not the true waveform but an artifact of the Arduino input stage and sampling process. What frequency is your Arduino sampling at?.

When diagnosing problematic digital signals in the MHz range, you really need tools you can rely on that don't send you on wild goose chases.

When you say you tried it with your signal generator and it was accurate, what waveform and at what frequency did you set your signal generator to? Try setting a 10MHz square wave at 0-5v and see if the CRO is accurate with that, if it is, (which I doubt), then you should be fine to use it for testing/probing on the Gigatron.
DevilledEggs
Posts: 8
Joined: 23 Nov 2021, 23:24

Re: Nonfunctional Gigatron.

Post by DevilledEggs »

at67 wrote: 27 Nov 2021, 02:46 Dodgy Arduino HW/SW CRO's can be super misleading on digital circuits in the MHz range, they are usually fine for Audio and KHz, but I wouldn't trust what you are displaying.

e.g. Are the units per division correct? If they are then those signals are rubbish, also the signal with ringing/undersampling, (the one you labelled as a better signal), would be breaking TTL noise immunities with a waveform like that. But I would guess that's not the true waveform but an artifact of the Arduino input stage and sampling process. What frequency is your Arduino sampling at?.

When diagnosing problematic digital signals in the MHz range, you really need tools you can rely on that don't send you on wild goose chases.

When you say you tried it with your signal generator and it was accurate, what waveform and at what frequency did you set your signal generator to? Try setting a 10MHz square wave at 0-5v and see if the CRO is accurate with that, if it is, (which I doubt), then you should be fine to use it for testing/probing on the Gigatron.
That makes a whole lot of sense, the oscilloscope I ordered is hopefully coming tomorrow. The signal generator was set to a lower frequency, thus making my tests a little bit unreliable. I think the new oscilloscope will make my life a whole lot easier. As for the "Better Signal", Im not sure how I came to that conclusion, it doesn't seem correct.
DevilledEggs
Posts: 8
Joined: 23 Nov 2021, 23:24

Re: Nonfunctional Gigatron.

Post by DevilledEggs »

at67 wrote: 27 Nov 2021, 02:46 Dodgy Arduino HW/SW CRO's can be super misleading on digital circuits in the MHz range, they are usually fine for Audio and KHz, but I wouldn't trust what you are displaying.

e.g. Are the units per division correct? If they are then those signals are rubbish, also the signal with ringing/undersampling, (the one you labelled as a better signal), would be breaking TTL noise immunities with a waveform like that. But I would guess that's not the true waveform but an artifact of the Arduino input stage and sampling process. What frequency is your Arduino sampling at?.

When diagnosing problematic digital signals in the MHz range, you really need tools you can rely on that don't send you on wild goose chases.

When you say you tried it with your signal generator and it was accurate, what waveform and at what frequency did you set your signal generator to? Try setting a 10MHz square wave at 0-5v and see if the CRO is accurate with that, if it is, (which I doubt), then you should be fine to use it for testing/probing on the Gigatron.
I just got around to tuning the oscilloscope in and I am very pleased with it. It is a cheaper oscilloscope from amazon but it has a lot of functions my old vintage oscilloscope (heathkit) could only really dream of. I will be able to test the board tomorrow, as it is late inteo the night right now where I live.
lb3361
Posts: 122
Joined: 17 Feb 2021, 23:07

Re: Nonfunctional Gigatron.

Post by lb3361 »

I wanted to test my latest toy by measuring the lag between the two clock signals in the Gigatron. I was expecting 5ns but measured close to 20ns lag. This means that when the registers latch their data, the latch enable signal is still okay despite the fact that the instruction decoder has been working on new ones for already 20ns. Good that the diode forest is a bit slow! In fact, better avoiding fast diodes!
20211202_155116.jpg
20211202_155116.jpg (1.07 MiB) Viewed 260 times
The two traces are measured on respectively the CLK and CLK2 testing points on the motherboard. I believe one just has to remove C3 to basically eliminate this gap. I wonder whether Marcel and Walter expected it to be as big. The schematics talks of a 5n shift only.
rob.keij
Posts: 1
Joined: 05 Jun 2019, 11:46

Re: Nonfunctional Gigatron.

Post by rob.keij »

@ DevilledEggs

Is you board still not working?
Ik just build my one I bought several years ago and this one is also nog working.
All leds are on when I power up (D2 and then in sequence D5, D6, D7 and D8 and all stay's on)
Both clocks are ok with a shift of ~20ns.

I imported the design in Altium so it's easy for me for trouble shooting.
I got eprom version 3
lb3361
Posts: 122
Joined: 17 Feb 2021, 23:07

Re: Nonfunctional Gigatron.

Post by lb3361 »

I am not sure I am interpreting this right, but I read 1 v/div and 2ms/div on the right of the clock plot. That would mean the clock voltage is 1.5v instead of 5v, and the clock frequency three orders of magnitude below 6.25 Mhz.
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