6560/6561 related oscilloscope and vectorscope images

Modding and Technical Issues

Moderator: Moderators

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Fri Jun 17, 2016 1:27 pm

eslapion wrote:The ripple is undoubtedly caused by accesses to the screen codes in RAM and the character generator ROM.

I'd like to understand more about what we know of this phenomenon. I've seen it mentioned on here before a few times, and also remember seeing the visual effect. Where within the VIC 20 circuit and/or the VIC chip do we think this interference might be occurring? What is the current theory?

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Fri Jun 17, 2016 3:36 pm

lance.ewing wrote: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.

You already have that in the second capture of post #6. The border is black and the first character is blue. There is no spike.

Here:
Image

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.

That would make sense.

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

Actually it does. If the blanking turns off too early at the beginning of the scanline, it will turn on too early as well at the end.

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).

That is truly not up to me.
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Sat Jun 18, 2016 8:40 am

eslapion wrote:
lance.ewing wrote:It doesn't explain why there is a drop at the end of the right border though.

Actually it does. If the blanking turns off too early at the beginning of the scanline, it will turn on too early as well at the end.

Yeah, I think that might explain it. If the blanking luminance turns on before the blue gets cut off then I assume the combined pull down of the two would be lower than the blanking level.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Sat Jun 18, 2016 4:22 pm

@eslapion, would you be able to show the chroma channel now, and for the first request, could I see a change from dark blue to light blue? I had assumed until now that the full intensity colour was associated with the lighter shade, and the low intensity with the darker shade, but I'm starting to realise that it is probably the other way around. Seeing the increase or decrease in amplitude of the chroma signal would confirm this one way or the other. I'm guessing people probably already know the answer to this, but it would be nice to see the oscilloscope image.

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jun 18, 2016 4:47 pm

lance.ewing wrote:@eslapion, would you be able to show the chroma channel now, and for the first request, could I see a change from dark blue to light blue?

Here's my suggestion... I will set the border black, background color to light blue and put one solid space blue in the top left corner.

What you'll get on the scope are 3 steps: black(border), blue (1st character) and light blue (background).

I can also put a solid blue space in the top right corner and make another capture in the reverse order.

Would that give you what you need?
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Sat Jun 18, 2016 4:56 pm

Yeah, that sounds perfect.

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jun 18, 2016 5:02 pm

lance.ewing wrote:Yeah, that sounds perfect.

I will do that then. However, I am just back home from scuba diving, I am dead tired and starving. A good meal and a few hours of sleep are needed 1st.
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Mon Jun 20, 2016 6:59 am

Much appreciated. If it confirms what I suspect it will then I'll need to go back and edit one or two posts in the die shot analysis thread.

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Mon Jun 20, 2016 10:30 pm

Here they are...

This is the left border with 3 luminance steps, black, blue and light blue. The interesting thing here is I can no longer tell exactly where the transition from blanking to border is exactly as there is no longer a spike at the start of the border.

Image

Because of the limitations of the scope which cannot offset the trigger more than 4 divisions to the right, the end of the scanline was more difficult to capture and the horizontal resolution is one step lower.

Image
Here too, the transition from border to blanking cannot be identified. However, once more because of the limitations of the scope, you can see a bit of the sync at the extreme right.

Looking at these close ups, it seems my initial measure of 570mV for light blue was a bit too high. Seems more like 540mV.
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Mon Jun 20, 2016 11:42 pm

Apologies, it was the Chroma channel I was hoping too see that blue to light blue transition for. So exactly what you did for the setup but showing the chrominance. I'm interested in seeing if the light blue wave form has a lower or higher amplitude than the dark blue wave form.

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Tue Jun 21, 2016 1:58 am

lance.ewing wrote:Apologies, it was the Chroma channel I was hoping too see that blue to light blue transition for. So exactly what you did for the setup but showing the chrominance. I'm interested in seeing if the light blue wave form has a lower or higher amplitude than the dark blue wave form.

As I said earlier, the chroma channel is almost impossible to acquire because the colorburst phase is inverted on every field.

See:
viewtopic.php?f=14&t=8057&start=12
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Tue Jun 21, 2016 10:42 am

That's a shame. Oh well, I think I'm fairly sure that the light colours are low intensity and the dark colours are full intensity. This is the terminology used by the 6560/6561 datasheet for the low and high amplitude chroma wave. Although it doesn't spell it out as such, the chroma/luminance diagrams in the datasheet do strongly suggest that the low intensity/amplitude chroma is aligned with the higher luminance value for a given colour, and vice versa, that the higher amplitude chroma is aligned with the lower luminance value for a given colour.

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Tue Jun 21, 2016 11:28 am

@lance.ewing
If all you want from the chroma channel is the amplitude then I guess I could make a peak values capture instead of an average capture.
No one can do everything. Everyone can do something.

User avatar
lance.ewing
Vic 20 Devotee
Posts: 264
Joined: Sat Nov 10, 2012 3:19 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby lance.ewing » Tue Jun 21, 2016 11:52 am

@eslapion
If the peak values are not too difficult to measure then that would be great. It would be nice to confirm it absolutely.

I did have a number of chrominance related queries, but thinking it over now, I don't think it is going to be worth the effort, given it is very difficult to work with the chroma channel.

One image I was particularly impressed with was from your post here:

viewtopic.php?f=14&t=8057#p87780

Capturing the transition from one colour's phase to another's is quite a thing to see. It made me start wondering that in the absence of being able to make use of the vectorscope that you've borrowed that another way to attempt to measure the phase shifts for each colour would be to produce images like that one that show at what part of the wave (i.e. degree value) it starts from. It might be difficult to accurately align the image with a degree value though. We already know roughly what they are, so this approach isn't going to give something more accurate. And besides, it sounds like it would be extremely difficult to do, so perhaps the vectorscope is a better option to explore (if one can be acquired that can work with your s-video output).

eslapion
ultimate expander
Posts: 4331
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Tue Jun 21, 2016 6:39 pm

lance.ewing wrote:Capturing the transition from one colour's phase to another's is quite a thing to see. It made me start wondering that in the absence of being able to make use of the vectorscope that you've borrowed that another way to attempt to measure the phase shifts for each colour would be to produce images like that one that show at what part of the wave (i.e. degree value) it starts from.

Since this capture is from one single passage instead of an average of many repetitive acquisitions, it is very noisy.

It might be difficult to accurately align the image with a degree value though.

Actually, it's impossible for a simple reason. If you single capture the chroma, you cannot also capture the colorburst at the same time and you can't know the phase of the colorburst.

We already know roughly what they are, so this approach isn't going to give something more accurate. And besides, it sounds like it would be extremely difficult to do, so perhaps the vectorscope is a better option to explore (if one can be acquired that can work with your s-video output).

I think the vectorscope is a much better approach. I can rent a vectorscope that works with composite only but I can undo the S-Video mod.
No one can do everything. Everyone can do something.


Return to “Hardware and Tech”

Who is online

Users browsing this forum: No registered users and 7 guests