6560/6561 related oscilloscope and vectorscope images

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eslapion
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 6:26 am

I like this one:
In theory it would make sense that there are only 5 brightness
levels like on VICII, however for some reason in practice it
looks differently. Measuring the actual luma signal level
would clear things up.


Give me a chance to check on the VIC-II and I am quite sure there is more than 5 luminance levels.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby groepaz » Wed Jun 15, 2016 6:37 am

Remember how you teased and insulted me on Lemon64 when there was stuff I didn't understand about 6502 ML ? No, I won't do the same...

well, you just did. and yes, i understand it very well - i simply just read only the last post of yours and assumed you listed all numbers that you have.
Give me a chance to check on the VIC-II and I am quite sure there is more than 5 luminance levels.

dont bother.... marko makela did that ages ago click ... the comment is a bit misleading, as it refers to the very old first revision VICII (and doesnt count black) - the later ones obviously have 8 (9) lumas

edit: to get similar useful dataset, we'd need at least some numbers from a PAL VIC too.... and perhaps from some different revisions of the VIC too - at least i remember someone (pixel?) mentioning that he owns some VIC20 that looks kinda different to the "common" ones.

edit++: since your numbers differ significantly from what VICE currently uses, could you also tell the ripple range, and the exact VIC (as in the videochip) model?

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 6:56 am

groepaz wrote:edit++: since your numbers differ significantly from what VICE currently uses, could you also tell the ripple range, and the exact VIC (as in the videochip) model?

I don't have enough accuracy on the type of scope I have to be able to tell the amount of ripple. If you look closely at the regular spikes, it's obvious the noise comes from the VIC-I itself.

The VIC-I is a 6560-101 dated 4583.

My PAL VIC-20 has the VIC-I soldered on so making the S-Video mod would be damaging to the machine and I only have one monitor here which supports PAL and doesn't have an S-Video input.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby groepaz » Wed Jun 15, 2016 7:05 am

well, ideally you make those measurements "blindly" anyway (like marko did) so the impendance of the monitor input is taken out of the equation.... make a small basic program that prints the coloured blocks (or even type them out blindly, which might be a bit error prone though) and then put a probe on pin3 of the VIC...

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 7:38 am

groepaz wrote:well, ideally you make those measurements "blindly" anyway (like marko did) so the impendance of the monitor input is taken out of the equation.... make a small basic program that prints the coloured blocks (or even type them out blindly, which might be a bit error prone though) and then put a probe on pin3 of the VIC...

Even if I take the measurements "blindly", when a VIC-20 is modded for S-Video, you can't get the luma signal by itself.

The outputs of the luma-sync and chroma signal from the VIC-I have been designed to mix easily and as such they have a relatively high impedance output and the mixer in the VIC-20 literally adds the chroma onto the luma signal. There is only a 100pF capacitor separating the two. If you just tap on pin 3 (luma-sync), you get the chroma signal mixed in there anyways.

I know... I've tried that in the past.

Anyways, the impedance of the monitor has very little effect as there is signal buffering. Also, if the impedance of the monitor does have an effect, it changes the amplitude of the complete scale so there is no effect on the relative values. Everything will be squeezed proportionally.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby groepaz » Wed Jun 15, 2016 7:50 am

If you just tap on pin 3 (luma-sync), you get the chroma signal mixed in there anyways.

too bad... perhaps i can measure it myself when i get my scope back (which is currently used as a fancy visual effect in the studio of friend...lol)
Anyways, the impedance of the monitor has very little effect as there is signal buffering. Also, if the impedance of the monitor does have an effect, it changes the amplitude of the complete scale so there is no effect on the relative values.

yeah, but it'd make the values more comparable with markos stuff... and eg the ripple could be more visible

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 7:58 am

groepaz wrote:too bad... perhaps i can measure it myself when i get my scope back (which is currently used as a fancy visual effect in the studio of friend...lol)

If you have a PAL VIC-20 with S-Video mod, certainly.

Anyways, the impedance of the monitor has very little effect as there is signal buffering. Also, if the impedance of the monitor does have an effect, it changes the amplitude of the complete scale so there is no effect on the relative values.

yeah, but it'd make the values more comparable with markos stuff... and eg the ripple could be more visible

I scaled as large and as tall as would fit on my scope's screen. If the whole amplitude was greater then I would have to scale it back down to fit on the display so you'd be no better off.

What's really needed to get the exact amount of ripple is a scope with a higher resolution display and capture system. The TDS1002 has a very large scale capability but it captures in 8 bit and it's display resolution is 320x240. Not much...
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby groepaz » Wed Jun 15, 2016 9:50 am

If you have a PAL VIC-20 with S-Video mod, certainly.

i dont.... but i could put a socket between the VIC and the board and then disconnect the luma/sync pin from the rest and put the probe there
What's really needed to get the exact amount of ripple is a scope with a higher resolution display and capture system.

mine is a philips 3320A - should do the trick hopefully :)

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 2:55 pm

@Groepaz
I will try to snatch a capture of the ripple from a white on white and a black on black display.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 10:52 pm

When using white, the voltage delta between the blanking interval signal and the screen signal is so high that I can't get a trigger on the scope anymore when zooming big.

If I use black then there is no voltage difference between the end of the blanking interval and the beginning of the screen - you can't tell where the transition is. I decided to use a blue border with blue screen setting (POKE36879,110). The shift between blanking interval and border is minimal so I can zoom vertical scale the most yet you clearly see sync, blanking and border.

This is an average of 128 captures to completely remove external noise at 50mV/Div:
Image

You can see a tiny bit of the end of the sync on the left, the end of the blanking mostly in the middle and the beginning of the blue border on the right.
Last edited by eslapion on Thu Jun 16, 2016 10:32 am, edited 1 time in total.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 11:06 pm

Next I set the screen background to black (POKE36879,14) while maintaining the blue border so we can clearly see the end of the blanking, the border and then the background time intervals.

You can see the regular big/small/big/small bumps in the border beginning 2us before the text area.

Image

The spike just before the border was separately measured at 450mV in amplitude above black/blanking level.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Wed Jun 15, 2016 11:20 pm

This is a close up of the horizontal blanking and sync: On the left is the end of scanline 54, on the right is the start of scanline 55

Image

You can see there is no ripple in the right part of the screen on scanline 54 (left on the scope) and in the right border area just before the sync of scanline 55. Since the ripple begins 2us before the actual text area on the left, I assume it also stops 2us before the border on the right (you can actually see the last bump on the extreme left of the capture). The ripple is undoubtedly caused by accesses to the screen codes in RAM and the character generator ROM.

You can see the sync lasts 5us and is 350mV below black level. The rest of the blanking interval has exactly the same luminance level as ordinary black. You can also clearly see the right border is much shorter than the left one.

Tom? Lance ? Need more ?
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jun 17, 2016 1:57 am

I do have other requests, but as I'm struggling to find time to sit down at a PC at the moment (this is from my phone), I'm going to type the shortest one. It's in relation to that spike between the blanking and border. What do we think that is? Does it happen if you alternate between blue and black across the screen? If not then I'd be struggling to think why not, as black & blanking are effectively the same thing as far as the output goes.

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Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Fri Jun 17, 2016 3:05 am

lance.ewing wrote:I do have other requests, but as I'm struggling to find time to sit down at a PC at the moment (this is from my phone), I'm going to type the shortest one. It's in relation to that spike between the blanking and border. What do we think that is? Does it happen if you alternate between blue and black across the screen? If not then I'd be struggling to think why not, as black & blanking are effectively the same thing as far as the output goes.

This spike occur only with colors having a luma level of less than 450mV, that's red, blue and purple but not with black and only at the beginning of the left border.

However, you can also see there is a downward spike at the end of the right border (see last capture) if the border color is anything other than black and the intensity of the spike is in direct proportion to the luminance level of the border color - it is about 1/3rd the amplitude. Example: In the last capture, the border is blue and has a luminance level of 200mV above black so the downward spike is about 66mV.

If you look at the transition from border (blue) to text area (black), there is no spike there so this is specific to the transition from blanking to border and inversely and only if the border color isn't black.

I can only assume this is caused by the architecture responsible for activating/deactivating the blanking.
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Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jun 17, 2016 1:15 pm

eslapion wrote:This spike occur only with colors having a luma level of less than 450mV, that's red, blue and purple

Yeah, I can see how it would not be noticeable above 450mV, since it would presumably be seen simply as part of the rising edge of the higher value.

eslapion wrote:but not with black and only at the beginning of the left border.

This is interesting.

eslapion wrote:However, you can also see there is a downward spike at the end of the right border (see last capture) if the border color is anything other than black and the intensity of the spike is in direct proportion to the luminance level of the border color - it is about 1/3rd the amplitude. Example: In the last capture, the border is blue and has a luminance level of 200mV above black so the downward spike is about 66mV.

Yeah, I can see that now that you mention it. That one is even stranger. Why would it drop below the black/blanking level in that scenario? The only situation it should drop below that level is during a sync pulse.

eslapion wrote:If you look at the transition from border (blue) to text area (black), there is no spike there so this is specific to the transition from blanking to border and inversely and only if the border color isn't black.

I was interested more in the transition from black to blue within the video matrix part of the screen. I think that would better match the start of the left hand border. But having said this, blue to black would match the end of the right hand border, so the absence of the downward spike is interesting.

It is also very strange that the spike doesn't happen when transitioning from a black border to blanking. That isn't explained by any of my current theories, so could be a key observation for tracking down what is happening.... Although, now that I think about it, there are a number of things different about black that might explain it.

eslapion wrote:I can only assume this is caused by the architecture responsible for activating/deactivating the blanking.

Yeah, it's bit perplexing. I guess we might need to wait to see what the measurements look like for a 6561E, i.e. to match the die shot, since at present I've got the 6561E die shot in my mind and struggling to understand the spikes based on that. In that die shot, black and blanking are equivalent for the purposes of generating the luminance output. Both the blanking and black signals are inputs to the same OR whose output then pulls the luminance to the required value, so in theory there shouldn't be a difference between switching from blanking to blue or from black to blue. - I wonder if it is something to do with timing then? Maybe the blue signal doesn't kick in immediately at the same time as the blanking turns off, and so the luminance level starts getting pulled up momentarily, as there's no pull down at all during that moment, and perhaps the black kicks in quicker.

It doesn't explain why there is a drop at the end of the right border though.

Any chance we might get a 6560 die shot at some point? Would be very interesting for comparison with the 6561E. I've seen at least one web site currently selling them and its a website I trust (as I've used them for other components in the past).


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