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Cbm 2001 Pet strange boot

Desperado

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We have already given you the next step if you go back and re-read the posts...

See 1730, 1732, 1733 and 1735.

You need to select the correct timebase for the signal you are trying to observe and then adjust the trigger level.

Based on what I see in post #1735, I would set the timebase to 1 us/div as the best compromise. Slower than I would like (0.25 us/div as I have calculated) but you should, nevertheless see some pulses.

Observing NO pulses doesn't mean something is wrong. The questions is, WHAT are you observing with that timebase setting. Only you can determine that - not me and not Hugo.

Dave
I'll try this tomorrow but i have already tried with all divisions and i haven't seen pulses :(
 

daver2

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I stated in my last post that you may NOT see pulses - but I want you to TRY.

I also want to see the oscilloscope trace results when you have that setting configured.

Dave
 

Hugo Holden

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Desperado,

If you cannot get the scope to show you any stable locked pulses, you could try your logic probe and at least help to confirm if there are pulses there or not.

Your scope display suggests they are there , it is just you cannot see a sync'd individual pulse. This can happen when the pulse has a short duration of less than a few hundred nanoseconds and if the pulses are relatively widely spaded.

Most logic probes contain a circuit that can detect pulses and an LED to show if they are there, or not.
 

daver2

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Is it me that is being stupid (?) but I see some sort of wave on the oscilloscope screen!

I assume the only thing you are measuring is UD9/20?

Is it a 5V signal I see? I can’t see because of the dark lighting...

Dave
 

Desperado

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Yes Dave, only Ud9 pin 20....i can see this waveform but with weak light :(
I have this setting:
 

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SiriusHardware

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I think this:-

Pulses.jpg

....Is what Dave is referring to. You can't see those pulses, Desperado?

For any future captures try putting tape or some other mask / cover over the LEDs on the scope because they are so bright in comparison to the rest of the scene that they are making the camera reduce the overall exposure level to compensate for their brightness, making everything else darker.

I'm not sure what that bright spot, lower centre is either - possibly the illuminator on the phone you are filming with. Try to turn that off as well so it doesn't get reflected back to the camera by the screen.

Edit: I see Desperado has now managed to see them.
 

Desperado

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I think this:-

View attachment 1243230

....Is what Dave is referring to. You can't see those pulses, Desperado?

For any future captures try putting tape or some other mask / cover over the LEDs on the scope because they are so bright in comparison to the rest of the scene that they are making the camera reduce the overall exposure level to compensate for their brightness, making everything else darker.

I'm not sure what that bright spot, lower centre is either - possibly the illuminator on the phone you are filming with. Try to turn that off as well so it doesn't get reflected back to the camera by the screen.

Edit: I see Desperado has now managed to see them.
Ah these are pulses?? Wow!
I thought the impulses must be external to the wave....
The green light is the power button s' led :)
 

SiriusHardware

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OK, well, cover the 7-segment LEDs, AND the scope's power LED the next time you are trying to film footage or take photos from the screen. Both of those bright light sources are influencing the camera's light metering and making the picture too dark over all.
 
Last edited:

daver2

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Right, a little more training called for now...

As you increase the speed of the timebase, the spot of light is flying faster and faster across the screen and imparting less energy to the phosphor. Less energy means less brightness. There SHOULD be a BRIGHTNESS control on your oscilloscope. How about turning that UP rather than turning the house lights DOWN :)?

More knobs to play with!

However, if you slow the timebase down again, don't forget to turn the BRIGHTNESS down - otherwise you could damage the phosphor on the screen over time. Plus you would dazzle yourself...

Now what I want to know is what is the voltage swing of the top of the waveform from the bottom and how many divisions (from leading edge to leading edge - or trailing edge to trailing edge) the signal is. At 1 us/div, this should give us the approximate period of the pulses and then we can calculate the frequency - which (we should already know) should be 250 kHz (based on a 1 MHz CPU clock and 4 cycles of the clock per NOP instruction). This just makes sure we are reading the correct thing (rather than random noise)...

Dave
 

Desperado

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But i don't understand if i have also Ch1 line on screen.....if i move CH1 vertical position (strobe not connected) i can move one horizontal line...i am desperate!
 

daver2

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What are you measuring on channel 1? We haven't told you to connect channel 1 to anything (have we)? I am lost now.

2 divisions at 1V/div is 2 Volts. This is not a TTL signal... Not sure what you are measuring there?

You are supposed to have channel 2 connected to UD9/20. Channel 1 not connected - with the trigger set to channel 2.

Dave
 

Desperado

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What are you measuring on channel 1? We haven't told you to connect channel 1 to anything (have we)? I am lost now.

2 divisions at 1V/div is 2 Volts. This is not a TTL signal... Not sure what you are measuring there?

You are supposed to have channel 2 connected to UD9/20. Channel 1 not connected - with the trigger set to channel 2.

Dave
Now i have connected only ground of CH1 probe....
 

SiriusHardware

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Maybe need i set scope not on Dual?

If I understand correctly that you are being asked to use only channel 2 at the moment, then the CH1 / CH2 / DUAL / ADD switch currently needs to be set to CH2, not DUAL. This will also make the CH2 trace a little bit brighter.
 

daver2

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Maybe can i try with logic probe on ud9 pin 20?

We are not looking for pulses on UD9/20. We have already seen UD9/20 change state previously.

What we are trying to do is to use UD9/20 as an oscilloscope trigger point for us to do some measurements on the data bus using channel 1.

Using the logic probe is, therefore, irrelevant.

Please do what @SiriusHardware has suggested above for the time being.

Unfortunately, you are going to have to learn how to take measurements using your oscilloscope with two channels. It took us a while last time we did this - we just have to educate you a bit more - that's all :)...

Dave
 

Hugo Holden

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Desperado, back in post #1712 Daver2 gave you the instructions about using Channel 2 to look at the pulses on UD9/20.

When you are using just one scope channel like this, it works much better, as noted by SiriusHardware if the scope is not in dual mode, because you will always get a brighter beam, with the single trace only and not a double trace.

Sometimes, in the DUAL channel mode, the effect of the Chopping process inside the scope, between channels (and channel 1&2 beams on the CRT face), can produce artifacts (a false signal) that might look like real signal but it is just the scope chopping between beams, like you have seen in your video post #1747, but is not a real signal at all, this tends to happen, when it does, at very fast (short) time-base settings.When this becomes problematic often using ALT rather than CHOP can help.

So follow Daver2's and SiriusHardwarte instructions exactly and for now just channel 2 operating, not in DUAL mode, and see if you can find and lock the pulses on UD9/20 if they are there.
 
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