derkom's doings

[derkom]

That looks massively sub-sampled. Is your 'scope able to resolve that frequency?

Oh it definitely is that, but bear in mind this is 32 MHz, which pushes the sampling limits of cheap equipment. I'm using a Digilent Analog Discovery 2, and unless there's something I'm missing, this is about the limit of its resolution.

[exxos]

Oh it definitely is that, but bear in mind this is 32 MHz, which pushes the sampling limits of cheap equipment. I'm using a Digilent Analog Discovery 2, and unless there's something I'm missing, this is about the limit of its resolution.

You need at least x4 frequency to get proper rate. IE you need 100Mhz scope to get even half decent 32MHz wave.

EDIT:

I'm trying to measure my 32Mhz, I have 3 probes, and regardless of X1 or X10 I get all sorts of bizzare voltages :roll:

[exxos]

Right...

IMG_5278.JPG

Don't forget the 32Mz also has 68R on the PCB anyway... I use a 100R as well for tests...


X1 probe 4V (before resistors)

IMG_5277.JPG

X1 probe 2.5V (pin 1 of GAL ~168R)

IMG_5279.JPG

X10 probe 4V (X10 gain on pin 1)

IMG_5280.JPG

So X1 probe loads the line a fair bit and drops from 4V to 2.5V!

X10 probe has little effect and still manage to get 4V on pin 1 of the GAL even with 168R series resistance.

So either your scope or F-chip is FUBAR... if you are getting 1.7V...

[derkom]

So either your scope or F-chip is FUBAR... if you are getting 1.7V...

FWIW, the specs of the AD2 say "Two-channel USB digital oscilloscope (1MΩ, ±25V, differential, 14-bit, 100MS/s, 30MHz+)". But, I learned a lesson here about how to use it, which is do not use the realtime display if wanting to get a good representation of high frequency stuff, because USB bandwidth becomes the limiting factor.

Instead, setting up a trigger and using the scope's internal memory, here's what I see now on the buffer chip pin 4:

CLK32-F.png

Obviously still doesn't have the sample rate of your Rigol, but I seem to be getting a much better representation of the p-p voltage now, and it basically agrees with yours. The cap board is installed and everything seems fine at 8 MHz with no 32 MHz wire installed, so I'll move on now to working with the 32 MHz hookup again.

[exxos]

Obviously still doesn't have the sample rate of your Rigol, but I seem to be getting a much better representation of the p-p voltage now, and it basically agrees with yours. The cap board is installed and everything seems fine at 8 MHz with no 32 MHz wire installed, so I'll move on now to working with the 32 MHz hookup again.

Yeah 3V is more like it is supposed to be. CBA to look up the F series output voltage, but likely is about 4V, and then drops a little after the resistors to pin 1 of the GAL. As long as its over 2.5V it should be fine.

[derkom]

Replaced the 32 MHz clock wire with a fresh piece of wire and here we are ...

IMG_20200612_190545.jpg

Can't swear it's long term stable yet, but the other wire was definitely the main source of the latest issues. Since it was working nearly okay the first time I hooked it up, and got progressively worse, I think it was just subject to too much manhandling and wasn't reliable for high frequencies anymore. 32 MHz looks nice on the scope now, and so far no crashes. Crossing fingers.

Oh, and I didn't route the long way around. Went along the right side of the shifter and then across, as before, and that seems fine thus far.

[exxos]

:thumbup: My wire is just all over the place. You have to use the thin wire.. It adds some resistance which helps , larger wire may well need another 100R resistor in series with it.. but its nothing I ever tested out.

I'm testing my new firmware out, and its crashed a couple times, but wouldn't even get much past desktop when using the MB 8MHz clock.. really odd as it had been running in the past just fine. Though I started test again with the 100R and see how things go now.

https://www.exxosforum.co.uk/forum/viewt ... 270#p41270

[derkom]

:thumbup: My wire is just all over the place. You have to use the thin wire.. It adds some resistance which helps , larger wire may well need another 100R resistor in series with it.. but its nothing I ever tested out.

Since I don't have any really fine wire (got some on order though), I butchered a SATA cable to pull the wires out of that. Got plenty of those, since every motherboard for every PC I've built in the last decade has come with at least four, and I'm typically using only one or two. They're probably 28 AWG, and maybe the wire you provided was 30? Running without any added resistors right now. I'll check later what the p-p voltage looks like. I don't have the scope hooked up right now, and I want to leave GEMBench running.

[derkom]

IMG_20200613_082822.jpg

Okay, it is stable. Of course now I don't want to touch anything. It will have to live on my desk forever. :lol:

[exxos]

Okay, it is stable. Of course now I don't want to touch anything. It will have to live on my desk forever. :lol:

Good plan ;) mine got turned off at 124 loops.