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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 4th Feb 2024, 5:49 pm   #1
Erik-Jan
Diode
 
Join Date: Feb 2024
Location: Eindhoven, The Netherlands
Posts: 2
Default 819line video from a PC without software tools

Hello,
Let me first introduce myself;
My name is Erik, living in Eindhoven, the city of Philips.
And active in restoring vintage TV`s from the '40 en 50.
I've been a frequent reader of this great forum, and now finally decided to join this comunity.
English is not my native language, so I hope I can be forgiven for some language errors.

The first project i want to discuss is generating 819 line video using a standard windows-PC VGA output.
Of course this is done before, but is always required manual changing of the video settings, using a specialized program.

My idea is to use the VGA EDID data to force the video-card into the desired resolution.
EDID is the handshake a PC en monitor do when connected together,
In it simplest form it tells the name of the monitor and the supported resolution(s) of the monitor.

The goal is to come up with a plug-and-play solution which will work on as many videos adapters as possible.
So i tinkered a simple interface together.
The EDID data is stored in a 24CL02 eeprom, and contains the monitor name (819L to VGA) and only one allowed resolution (1200x776).
(The binary file for the EEProm can be created using CRU 1.5.2)

I tried this setup on three different PCs (coincidentally all with a HP video adapter).
The results are mixed, on all PC's the interface is automatically recognised, but only two PC's start outputting video.

I think a solution in getting this to work the best lies in the combination of choosing the right pixel clock speed and horizontal/vertical pixel count.

This brings me to my first question, what pixel clock to choose which will work on most video cards?

Greetings Erik.
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Old 5th Feb 2024, 7:32 pm   #2
marceljack
Hexode
 
Join Date: Apr 2021
Location: Paris, France.
Posts: 256
Default Re: 819line video from a PC without software tools

Hi Erik-Jan,
Welcome to the forum.
Your idea is very interesting however I wonder if it can work with all graphics cards or chips.
A long time ago (in the early 90's) I reprogrammed VGA cards in order to make them work in 640 x 480 on the SCART connector of a 625 lines TV.
Different graphic chips used different ways to be put in interlaced mode, so I had to write different routines for different chips.
I did that under DOS by means of a so-called TSR routine (Terminate and Stay Resident).
I dont think EDID existed at that time.
For your information, I was working at Philips Semiconductors France, so I went relatively often to Eindhoven.
Sorry not to be more helpful !

Greetings

Hervé
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Old 6th Feb 2024, 1:09 am   #3
Maarten
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Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,284
Default Re: 819line video from a PC without software tools

Welcome, fellow Dutchman!

While HP writes some of the specifications, multiple factors such as the video chip, the BIOS and the drivers determine whether the EDID method will work. I think it would be useful to document at least the actual video chip as the other factors are often based on reference designs for this chip.

In your picture, I see an (onboard) Intel HD Graphics 520 videochip.

@marceljack: I think you just missed DDC and later EDID by a few years, not too much in any case. Philips monitors made in the mid 1990's already supported at least DDC.
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Old 6th Feb 2024, 8:24 pm   #4
Erik-Jan
Diode
 
Join Date: Feb 2024
Location: Eindhoven, The Netherlands
Posts: 2
Default Re: 819line video from a PC without software tools

Thank you

EDID has indeed known several versions. The interface now works according to the 2.1 standard.
I have now tested with 4 different laptop PCs, all with an onboard HP video card
All PCs recognize the interface, that is positive.
Two PC`s start indeed outputting video in the correct resolution.
One with a Intel HD Graphics 520 chip and one with a HP GMA4500 chip.

The third and fourth PC are not changing the output resolution.

Until now the results are pretty much hit or miss

I think there is some "sweet spot" in the relation between line/frame timing and the chosen pixel-clock.

Greetings Erik
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