RGB to VGA

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ADKM

860 posts

Ultimate Geek

#153513 29-Sep-2014 18:11

After more years that I can remember my Commodore 1084 monitor has died. Sometimes I still want to
play with the old Commodore 128 and that may be a problem now. Yes, I can use composite mode, but the 80
col RGB signal is more essential.

Will this do this trick, or is there more to it?

Alternatively, does anyone know of modestly priced adapter or convertor?

Thanks.

Lurch

1061 posts

Uber Geek

#1143718 29-Sep-2014 18:28

This is a good read :-)

https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga

ADKM

860 posts

Ultimate Geek

#1143785 29-Sep-2014 20:16

Thanks Lurch, that was very worthwhile. I'll have a crack at the simple 16 Col circuit onto some veroboard and see what happens!

One puzzling thing - he says Because I don't own the VGA adapter he does, I added 1k Ohm variable resistors to all the VGA output lines (except ground). These are not shown in the schematic (may not be needed, depending on tolerance of VGA converter that you use).

Can't quite figure what he means by 'VGA adapter' and 'VGA Convertor'. Does he mean the VGA screen ?

Mark

1653 posts

Uber Geek

#1144050 30-Sep-2014 10:26

Hiya,

What the design on the website posted previouly does is to take the digital RGBI from the C128 and convert it to analog RGB, you will still need to either find a VGA monitor that will sync down to 15Khz horitzontal or find a CGA to VGA converter (CGA basically being the analog version of what the C128 outputs)

Problem there is that you'll get yellow output when you are expecting brown (Commodore tweaked their monitors), and you may have issues with the 50Hz vertical refresh.

I've a bunch of links to a good converter setup with brown fix at home, I'll dig them out for you later. I also did my own design but haven't gotten around to building it yet.

Oh and I might be a bit of a C64/128 nerd too ;-)

ADKM

860 posts

Ultimate Geek

#1144159 30-Sep-2014 13:16

Hi Mark, Looks like the plot thickens. I wouldn't like to try building a converter and I'm not sure how you determine if a monitor will sync
down to 15Hz horizontal. (I have a couple of older CRT ones). Wasn't going to overly worry about brown/yellow to start with, would have
been happy enough just to see something on the screen!

I don't use the 128 enough to spend a lot of money on (and it might fall over any day) but it has been useful looking at some old stuff I'd written
and converting them to VB. I did make something that would LIST a .PRG file with all control keys in square brackets a bit like Computes Gazette listings.
Also have a working 1571 and 1581 and (somewhere) a 512k mem expander.

Mark

1653 posts

Uber Geek

#1144184 30-Sep-2014 13:43

ADKM: Hi Mark, Looks like the plot thickens. I wouldn't like to try building a converter and I'm not sure how you determine if a monitor will sync
down to 15Hz horizontal. (I have a couple of older CRT ones). Wasn't going to overly worry about brown/yellow to start with, would have
been happy enough just to see something on the screen!

I don't use the 128 enough to spend a lot of money on (and it might fall over any day) but it has been useful looking at some old stuff I'd written
and converting them to VB. I did make something that would LIST a .PRG file with all control keys in square brackets a bit like Computes Gazette listings.
Also have a working 1571 and 1581 and (somewhere) a 512k mem expander.

Well pretty much no modern screens go down to 15Khz .. that's basically ye olde CRT television days, though something like an arcade monitor would most likely work.

I've far to much Commodore gear but usually I'll break out the original kit when I have a new bit of hardware to play with (got a nice 8 player joystick adapter lately that i still have to plumb in) but all my real 1084 monitors have died.

Nowadays when I want to play something retro I use an FPGA based Chameleon to "emulate" the C64 or Amiga or Spectrum or MSX on a VGA monitor :-)

Lurch

1061 posts

Uber Geek

#1151200 10-Oct-2014 11:16

ADKM: Thanks Lurch, that was very worthwhile. I'll have a crack at the simple 16 Col circuit onto some veroboard and see what happens!

One puzzling thing - he says Because I don't own the VGA adapter he does, I added 1k Ohm variable resistors to all the VGA output lines (except ground). These are not shown in the schematic (may not be needed, depending on tolerance of VGA converter that you use).

Can't quite figure what he means by 'VGA adapter' and 'VGA Convertor'. Does he mean the VGA screen ?

You'll need to purchase a GBS-8220. Pretty cheap on ebay.