VGA --> RGB for 1084S Monitor (solved!)

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NegSol
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VGA --> RGB for 1084S Monitor (solved!)

Postby NegSol » Thu Nov 02, 2017 2:36 pm

I just completed a cable to input the VGA of the MiST into my old 1084S D1 CRT Monitor using the 9 pin RGB input. After disabling the scandoubler in the MiST.ini I got a perfect picture on the MiST, just like I got from my old machines.

Trying the same cable with the MiSTer I was not as lucky. MiSTer shows a rolling picture on the 1084S Monitor. I know that the 1084S only requires H.sync and I use the composite sync for this. As it works perfectly with my MiST, it should work with the MiSTer too, or am I wrong?

My MiSTer.ini settings:

forced_scandoubler=0
ypbpr=0
composite_sync=1
vga_scaler=0

I tried all other combinations in ini however nothing changes. Not even when I enable the forced_scandoubler.
Actually the fact that nothing changes, even when I for example enable the scandoubler makes me wonder if I set up the MiSTer.ini file correctly. Enabled scandoubler on the MiST would give me no picture on the 1084. Maybe the MiSTer.ini settings are not read by MiSTer for some reason.

Anyway here are some pictures and a link to a video showing the rolling effect

https://youtu.be/GLWY14qhciM

Any ideas, what the matter could be? :shrug:
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Last edited by NegSol on Fri Nov 03, 2017 7:27 am, edited 1 time in total.

Sorgelig
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Re: VGA --> RGB for 1084S Monitor

Postby Sorgelig » Thu Nov 02, 2017 3:22 pm

Your MiSTer.ini settings are correct. Need further testings as VGA output on MiSTer is not main video output.
Do you have oscilloscope to check the hsync/vsync signals?

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 3:32 pm

Sadly I have no real oscilloscope. I can only test it against the MiST output (i.e. direct comparison). But this is of limited value. Actually I did know that the VGA Output of the MiSTer is mainly used for development. I guess I just was happy that the old monitor worked on the MiST first try with the cable I built. That is why I tested it on the MiSTer. I would not consider it a major use case. But I guess it would be great to get this to work at some point :P

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Re: VGA --> RGB for 1084S Monitor

Postby Sorgelig » Thu Nov 02, 2017 3:44 pm

I will look at this issue sometime later.
Too much to do for a single dev.

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 4:02 pm

I understand - no problem - It is not urgent :mrgreen: :)

I used my shoddy DSO138 Oscilloscope to get a reading on the H sync pin (VGA pin 13). Both MiSTer and MiST looks very similar. MiST looks more stable though and MiSTer signal seems to disappear in regular intervals. Maybe this is a clue. But again - I am no expert and am not used to reading this kind instrument.

https://youtu.be/-1e4JUef6qE MiSTer Sync Signal (VGA Pin 13)

https://youtu.be/LTZ-2KRHY9w MiST Sync Signal (VGA Pin 13)

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 4:22 pm

I noticed the AC setting - But switching to DC I get the same result. MiST signal is more stable - I guess...

https://youtu.be/NehqqL0LohY MiSTer - Sync Signal - VGA Pin 13 (close up DC)


https://youtu.be/7R7baKwap3Y MiST - Sync Signal - VGA Pin 13 (close up DC)

Sorgelig
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Re: VGA --> RGB for 1084S Monitor

Postby Sorgelig » Thu Nov 02, 2017 5:53 pm

your oscilloscope shows horizontal sync. It's not visible how vertical sync is mixed.
Anyway, try some other cores like ZX or BK0011M - they should work similarly to MiST versions.

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 8:08 pm

Thank you for your suggestion. The picture rolls on the MiSTer RGB connection independent of the core in use. The 1084S offers a so call Analogue RGB which works without vertical sync. Vertical sync is identical to composite sync here. It has not vertical sync for analogue RGB at all. It also offers a TTL RGB which is a digital RGB and uses both horizontal and vertical sync. However I am quite sure MiSTer will not support TTL as this was only used for PC CGA back in the day. Also TTL uses different volt settings and would require some inline resistors. Maybe I wrong.

Anyway - again - not so important, as the monitor works fine with the RGB connection on my MiST. I just wonder what the difference to the MiSTer could be. :shrug:

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 8:29 pm

Okay - I have a hunch of what could be going on.
I read that the old analogue RGB of my 1084S uses a combined H.Sync/V.Sync that is outputted by some old machines (amiga and genesis) on the same pin as the composite sync signal. Maybe the MiST simulates this somehow?

NegSol
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Re: VGA --> RGB for 1084S Monitor

Postby NegSol » Thu Nov 02, 2017 8:54 pm

Just to show how the setup works on the MiST

https://youtu.be/JBBZwuAqF54 MiST RGB on 1084S

Sorgelig
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Re: VGA --> RGB for 1084S Monitor

Postby Sorgelig » Fri Nov 03, 2017 1:38 am

MiSTer outputs the same VGA with composite sync as MiST. Why it doesn't work for you - i have no idea now.
I'm using external scaler which supports several kinds of video input, and composite sync is one of them. And it works. So, basically composite sync works on MiSTer.

If you have PAL TV with SCART, then try it with MiSTer. You can use the same VGA-SCART cable from MiST. At least ZX/BK0011M cores should work through SCART with composite sync option.

Another possible cause: Where you put your MiSTer.ini file?

NegSol
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Re: VGA --> RGB for 1084S Monitor (solved!)

Postby NegSol » Fri Nov 03, 2017 7:39 am

Again I have to thank you Sorgelig for pointing out the issue/solution.

Just in case other stumble into the trap, let me explain:
It was indeed the MiSTer.ini location. Actually I placed it in the /media/fat when it had to be placed in /media/fat/config (easy mistake I guess if you are used to how it is handled on MiST).
Also, I used an old version of MiSTer.ini which had (at least one) different parameter name in it. But there is more. I found out that one definitely should not edit the MiSTer.ini too much. I delete the line brakes "^M" ate the end of the header line (more a mistake than with intent) and apparently this also ensured the parameter not being correctly read. So please leave those line breaks in as well.

Thanks again Sorgelig for the help :-)

Here are some pictures to show the successful solution:
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NegSol
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Re: VGA --> RGB for 1084S Monitor (solved!)

Postby NegSol » Fri Nov 03, 2017 8:04 am

https://youtu.be/JHQbrtSgQso Video showing the working RGB output on MiSTer

:mrgreen:

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Re: VGA --> RGB for 1084S Monitor (solved!)

Postby seastalker » Fri Dec 01, 2017 10:22 am

I have said monitor and others and would LOVE such a cable! Any chance you plan to make a few of these?

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Re: VGA --> RGB for 1084S Monitor (solved!)

Postby bernouilli » Fri Dec 01, 2017 11:05 am

It's the same cable as for MiST, you can buy it from here :
http://lotharek.pl/product.php?pid=168

EDIT : This cable has a SCART connector at the other end and is for TVs.
But you can use the schematic to build your own cable for the 1084s.

NegSol
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Re: VGA --> RGB for 1084S Monitor (solved!)

Postby NegSol » Fri Dec 01, 2017 7:58 pm

@seastalker: sorry to disappoint - I am not producing the cable myself.

But as bernoulli stated - it is quit easy to make (no inline components - only direct connections to solder).

I used the following forum entry as reference
https://circuit-board.de/forum/index.ph ... t-Adapter/

vga pin assignment is the same as descrition on wikipedia:
https://en.wikipedia.org/wiki/VGA_connector

Ask if you run into any trouble... :D


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