6560/6561 related oscilloscope and vectorscope images

Modding and Technical Issues

Moderator: Moderators

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Mon Jul 11, 2016 12:33 pm

@A4000bear
Then the measured amplitude from sync "tip" to full white is considerably greater than 1V. It's more like 1.3V.

There are also important differences timing wise.

I assume CRT TVs can handle these differences much better than new digital TVs. For example my Planar PL1520M monitor has both a composite and an S-Video input and it displays TV/DVD signals perfectly well but only shows garbage with a VIC-20 or C64.
No one can do everything. Everyone can do something.

groepaz
Vic 20 Nerd
Posts: 597
Joined: Wed Aug 25, 2010 5:30 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby groepaz » Mon Jul 11, 2016 1:13 pm

old analog stuff is indeed much more tolerant to excess voltage there - its exactly the reason for why video cables with 330Ohm in series exist :)

a4000bear
Vic 20 Amateur
Posts: 47
Joined: Sun Jan 27, 2008 10:01 pm

Re: 6560/6561 related oscilloscope and vectorscope images

Postby a4000bear » Tue Jul 12, 2016 6:34 am

To clarify, the complete composite video signal should be 1V and is made up of two components. The sync signal which is 300mV and the white portions of the video signal which is 700mV. Adding them gives a total of 1V, which is what you see coming out of the VIC-20 (or any other video source).

Note that if your VIC is displaying a completely black screen, you will see only the 300mV sync signal.

Also note that the input on your monitor has to be terminated with 75 ohms, otherwise you may not get the correct 1V level. While all monitors should have this built in, some have a switch for this, make sure it is turned on before adjusting the VIC-20 for the correct 1V level. It goes without saying there needs to be at least some white in the picture too. The standard VIC 'boot' screen has a white inner background, so is good for this.

It is true that CRT TVs and monitors are far more tolerant of out of spec video levels compared to LCD monitors, some of which don't even display non interlaced video.

Incidentally the other trimpot in the VIC is there to control the DC level of the entire video signal. The RF modulator (if used) requires the video signal to be at an appropriate DC bias level for correct operation. It is not really critical for connection to a monitor. As I will never use a modulator, I prefer to adjust it so that the bottom of the sync tip is fairly close to 0V (you will need your oscilloscope set to DC coupling to see this). This is also a handy way of adjusting the sync level as sometimes it can be greater than 300mV....adjusting this DC level close to 0V can reduce the sync level slightly.

Tom
Vic 20 Amateur
Posts: 50
Joined: Mon Jun 06, 2016 9:07 am

Re: 6560/6561 related oscilloscope and vectorscope images

Postby Tom » Tue Jul 12, 2016 11:29 am

a4000bear wrote:Note that if your VIC is displaying a completely black screen, you will see only the 300mV sync signal.


Plus syncs and porches (including the colour burst), but it's pretty clear that I'm taking you massively out of context.

eslapion wrote:Can someone be kind enough to give me a recap of the captures I was supposed to do for you guys ?

I'm really sorry I let you down but 3 visits to the doctor as well as daily medication and all the stuff involved in dealing with postal problems with my customers took their toll. Add to that the guy who stole me a PLAnkton module.


Nobody's let down! I assume I speak for everyone in saying that anything you supply is pure bonus, being entirely voluntary and not exactly effort-free.

I had previously asked about vertical timing — on the NTSC chip in non-interlaced mode, does the vertical sync period end halfway through a horizontal line or at the end? Also is there any way to get a line count of the distance from end of vertical sync to the first line with pixels on it assuming you've just let the machine boot up naturally?

The former would confirm or deny my expectation re: why the line counter changes halfway through the line (i.e. I think this is probably a timer from vertical sync, and likely switches when it is incrementing in interlaced mode, but that's pure speculation), the latter would shed some light on where vertical sync occurs relative to the line counter. Probably either right at the top or right at the bottom, and with little practical difference, but if it is easy to find out then why not be sure?

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Fri Jul 22, 2016 7:16 am

I think I will have a bit of time to invest here today so here it is:
- VBI for Tom
- PAL captures for lance.ewing

But first, here is a slightly more detailed informative picture concerning the HBI in NTSC:
Image

I deduce from this image that 1 IRE=7.14mV

Also note that the VIC-20 black color is 0 IRE which is technically too low. This confirms my own VIC-20 has a video amplitude level about 30% excessive.

This means that "in proportions" my previous scope captures are good but their absolute values are wrong. I will have to adjust before I do any other capture.
No one can do everything. Everyone can do something.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jul 23, 2016 2:26 pm

Alright, the first capture for today is the HBI for scanline 56 which I have used with the normal VIC-20 startup color to adjust the video signal amplitude to normal values.

Image
The blanking level to white level is measured with cursors to 702mV which is just a tab lower than the target 714mV. What is not shown here is the digital measurement Pk-Pk voltage of 1.00 V from sync to white level. I made sure I used a border with a lower level than white to ensure the overshoot caused by the transition from blanking to border would not corrupt the resulting values.

4 steps are easy to see, the lowest is the sync followed by the blanking level, followed by the cyan border and then the white background. Gives you a good idea where everything is and that's close enough to what we saw in the HBI descriptive image.
No one can do everything. Everyone can do something.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jul 23, 2016 2:39 pm

Second capture is a general view of the VBI with the border still set to cyan.

Note the display is set to the normal non-interlace mode the VIC has by default.

Image
You can see the last 2 1/2 scanlines (bottom border of the screen) on the left, the VBI syncs in the center and then the first 4 scanlines of the top border on the right.
No one can do everything. Everyone can do something.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jul 23, 2016 2:45 pm

A closer view of the center section of the VBI with the border now set to white which results in the Pk-Pk voltage at 1.01V.

Image
You can see the sync pulses frequency now doubled compared to the displayable area.

An even closer look shows these pulses are about 2uS in duration.
Image
The amplitude of the syncs are 300mV which is pretty close to the target 266mV.
No one can do everything. Everyone can do something.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sat Jul 23, 2016 2:52 pm

On this last capture, I activated the interlace mode.

Honestly, on all captures of the VBI I was completely unable to see any difference between interlace and non-interlace mode. I expected to see a notable difference somewhere so this was a disappointment but I did notice the scope was unable to trigger on scanlines 1 to 4 without the interlace mode.

Here is a capture of scanline 1 with the interlace mode active.
Image
The very last scanline is on the left, the start of the VBI is on the right.

You can see the overshoot of the transition from blanking level to white border did corrupt the measure of the Pk-Pk voltage (it shows 1.03V).
No one can do everything. Everyone can do something.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sun Jul 24, 2016 4:59 pm

@Tom
Am I missing anything here ?
No one can do everything. Everyone can do something.

Tom
Vic 20 Amateur
Posts: 50
Joined: Mon Jun 06, 2016 9:07 am

Re: 6560/6561 related oscilloscope and vectorscope images

Postby Tom » Tue Aug 02, 2016 7:43 am

eslapion wrote:@Tom
Am I missing anything here ?

Apologies; I took a quick holiday: no, nothing missing as far as I can see! Thanks again for everything so far.

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Sun Sep 04, 2016 8:38 am

@lance.ewing
Did I forget something important you'd like to have captured ?
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 » Thu Sep 08, 2016 1:43 am

Right now I can't think of anything I'd like to see at the moment but if I do think of something, I'll add it in here. In theory I now have the equipment to do it myself, but not yet the experience or the time. Will give it a go at some point though. I've got four separate VIC 20 related projects on the go now. Lots of fun. :-)

eslapion
ultimate expander
Posts: 4330
Joined: Fri Jun 23, 2006 7:50 pm
Location: Canada
Occupation: 8bit addict

Re: 6560/6561 related oscilloscope and vectorscope images

Postby eslapion » Fri Oct 28, 2016 8:42 am

Postimage seems about to go bust. Their bandwidth provider is going to charge them 12'000$ a month and it seems unlikely they'll be able to foot the bill.

If the scope captures in here are any value to you then I suggest you capture the images and save them locally.
No one can do everything. Everyone can do something.

User avatar
joshuadenmark
Big Mover
Posts: 912
Joined: Sat Oct 23, 2010 11:32 am
Location: Denmark
Occupation: Copier technician

Re: 6560/6561 related oscilloscope and vectorscope images

Postby joshuadenmark » Fri Oct 28, 2016 10:16 am

Why don't you post images here in our forum, all the external image providers will disappear over the years, Denial will remain forever.
Kind regards, Peter.
____________________________________________________
In need of a wiki logon - PM me


Return to “Hardware and Tech”

Who is online

Users browsing this forum: No registered users and 2 guests