Output to VGA?

[Mangelore]

Mangalore - can you post some screenshots of GEOS 128 on the LCD?  Id like to see how it looks.  Am thinking of going ahead and getting one of those boards.

These converters look better when used with VGA CRT monitors. My LCD didn't scale the low resolutions that well.
Anyway, I had taken a screenshot of GEOS some time ago but it was on a VGA CRT monitor.
I must admit that GEOS looked great on the VGA monitor.

Here's the link. Once it pops up click on it again to view at full resolution.

[xlar54]

Ah damn... see...?  Now I was hoping it would look badly so I wouldnt drool, and now my computer desk is all wet.  THANKS..

Hehehe, seriously, thats a terrific thing.  The board is well worth it.  You might want to post the images in this thread on the intensity fix to that website (if its yours?).  Dunno if image shack eventually removes images or if thats a more permanent account.  Id like to get one and do exactly this.

Thanks

X

[RobertB]

Newsgroups: comp.sys.cbm
From: Wolfgang Moser <wn0...@d81.de.invalid>
Date: Mon, 12 May 2008 16:37:47 +0200
Local: Mon, May 12 2008 7:37 am
Subject: Fotios' C=128-RGBI-to-VGA hack with IBM-CGA color fix for brown

this is about Fotios' hack, where he used one of these CGA-to-RGB converter boards (WEI-YA ACV-011) and hacked it a bit to also accept the Intensity signal from a C128.

References are:
[ 1]   http://groups.google.de/group/comp.sys.cbm/msg/68460b84a2235969
[ 2]   http://groups.google.de/group/comp.sys.cbm/msg/4b85aac68ba2430d
[ 3]
http://landover.no-ip.com/forums/index.php?PHPSESSID=ia67jh0h7to8d3b2vinhq308q08&topic=453.msg2259#msg2259
[ 4]
http://landover.no-ip.com/forums/index.php?PHPSESSID=ia67jh0h7to8d3b2vinhq308q08&topic=2209.0

Well, Fotios surely based his work on other relating documents laying around at Zimmers (Funet) and other CBM archives:

[ 5]
http://www.zimmers.net/anonftp/pub/cbm/documents/cables/128-videocable.txt
[ 6]   http://www.softwolves.pp.se/cbm/maskinvara/scart
[ 7]   http://www.hardwarebook.info/C128_RGBI
[ 8]   http://en.wikipedia.org/wiki/Color_Graphics_Adapter
[ 9]   http://nemesis.lonestar.org/reference/video/cga.html
[10]   http://www.oldskool.org/pc/cgacal

There are two things with his work that I did not like much:
    a) You had to solder wires directly to the board
    b) To give a correct brown color, the IBM CGA palette
       fix needs to be applied


So I started hacking around myself. I got a WEI-YA ACV-011 CGA-VGA board from a polish reseller. I got a power supply with 12V for the converter board and 5V for my own circuits. First I looked out to verify Fotios' results on a simple hack without applying the Intensity signal. This worked fine, but I only had 8 colors [11].

Another drawback is that you desperately need a LCD/TFT monitor that accepts a refresh rate of only 50Hz. My main monitor does not want to accepts the signal from the ACV-011, I had to use a TV-LCD. That one is a bit too small (640x480) to show the 80 column mode with good quality. Well, it seems I have to buy a cheap 800x600 monitor.

I started with buffering the incoming signals with a 74LS244, this is a bus driver IC with integrated Schmitt triggers, just the same IC that is used in the C128 as output driver. Each signal, R, G, B, I, V and H is buffered by one of the drivers and I could work with the refreshed signals from the output stages. To mix the analog RGB colors, I used the resistor networks as shown in [5] or a simplified version of [6]. Since I only had resistors of 390 Ohms and 820 Ohms I used these instead of 470 Ohms and 680 Ohms:

                ______
     R/G/B   --|______|----+  390R
                           |
                           +------ R/G/B_analog
                ______     |
     I       --|______|----+  820R


For each of the three color components such a resistor network was built.

Then I went further to do this IBM CGA palette color fix that turns dark-yellow into brown [8]. I got a 74LS138 binary decoder and watched for the "magic" combination 1,1,0,0 for R,G,B,I. Once this was detected, another 80 Ohms resistor applied to the output channel for Green was pulled to Low level, otherwise it was switched to High level. So the overall resistor network for the
Green channel becomes:

                ______
     G (only)--|______|----+  390R
                           |
                           +------ G_analog (only)
                ______     |
     I       --|______|----+  820R
                           |
                ______     |
     C-Fix   --|______|----+  820R


This then changed the colors into a palette that should look fine [12]. But there is a slight imbalance with this design. With the Green channel _two_ 820 Ohms resistors are pulling to High level most of the time while on the other two color channels only one resistor pulls to High. This can be fixed a bit by giving the Green channel a special adjust on the ACV-011 input stage [14].

See the overall schematics with reference [15].

I already thought about a further improved color fix circuit which does the fix truly digital and with only applying 6 resistors instead of the 7 shown above. But there you would need a programmable logic chip so that the whole circuit does not become too clumsy.

I like the current solution very much since it just looks fine and I did not need to solder around directly on the ACV-011 board. I just need to get a nice case and a suitable well sized TFT monitor.


Bye, Womo

References:

[11] http://d81.de/shared/C=128-VGA/C128-Palette-wo-Intensity.jpg
[12]
http://d81.de/shared/C=128-VGA/C128-RGBI-Palette-with-CGA-IBM-Colorfix.jpg
[13] http://d81.de/shared/C=128-VGA/CGA-IBM-Colorfix-RGBI-DAC.jpg
[14] http://d81.de/shared/C=128-VGA/ACV-011-Board.jpg
[15] http://d81.de/shared/C=128-VGA/C=128-VGA-IBM-Colorfix.png

[RobertB]

     Just before last Saturday's SC3 Arcade Party in Claremont, California, I met up with Charles Gutman of 8-Bit Designs and bought his Fotios' re-engineered RGB-to-VGA adapter.  It came with the original manufacturer's not-so-helpful instruction sheet.  Time to try it out with CRT VGA and LCD VGA monitors!

                   Truly,
                   Robert Bernardo
                   Fresno Commodore User Group
                   http://videocam.net.au/fcug
                   The Other Group of Amigoids
                   http://www.calweb.com/~rabel1/

[Andrew Wiskow]

I met up with Charles Gutman of 8-Bit Designs and bought his Fotios' re-engineered RGB-to-VGA adapter.

Cool...  I got to see that one in action. 

[Jakit]

I distinctly remember that there was a discussion regarding some existing products which handled this function.
-------------------------------------
Information on c= to vga methodology.-------------------------------------

http://home.comcast.net/~kkrausnick/c128-vga/c128-vga.html
-------------------------------------
CGA To VGA Converter (800 x 600)
http://www.highway.net.au/parts/converters/1488.html-------------------------------------

RTV VEG Family of Products

The VEG Lite is a compact external unit that easily turns a VGA monitor into a gaming center, giving you enhanced 1024x768 resolution for your game graphics without having to take over the family television.
The VEG Lite can be used as a stand-alone game center or linked through your desktop computer.
http://www.rtv-veg.com/products/veglite/
connectors
http://www.rtv-veg.com/products/specs.php?prod=vegn

[klx300r]

thanks for the info Jakit!..havent played with my 128 in a while and hooking it up to an old vga monitor would be great...

[maraud]

Just an FYI that I got this to work, now that I finally got around to the final modification posted earlier.  All colors display now!!  I actually got one of these boards off of eBay for around $50.  Another $10 in parts and viola.  I was using a Veg Lite as indicated by an earlier poster but contiued to run into LCD scaling issues as my LCD was a 16:9 (off my Mac) so it didn't do a great job.  The 80 col only runs perfectly crisp on 640X480 derivative LCDs', (such as 800x600, 1025X768, etc).  the multiplier on my screen makes it less than square and therefore not perfect. 

However, I've found that I can get perfect 40col output on a little Dynex 15" LCD TV, and the 80 col works pretty darn well.  So for $160 it's a TV/Commie Screen 40/80 and I'm quite happy with the setup!

Thanks to Fotios for the "hack"!

PS, this lovely gem is making me smile now that I can run my 128 Telnet BBS in 80 col mode!!!
maraud.dynalias.com (port 6400)

[RobertB]

However, I've found that I can get perfect 40col output on a little Dynex 15" LCD TV, and the 80 col works pretty darn well.  So for $160 it's a TV/Commie Screen 40/80 and I'm quite happy with the setup!

That's good to hear.  I have the Fotios-modified 80-column adapter, but I have not tried it out with a LCD screen, due to the fact that not all LCD screens are compatible with it.

               Back from Maker Faire,
               Robert Bernardo
               Fresno Commodore User Group
               http://videocam.net.au/fcug
               July 25-26 Commodore Vegas Expo - http://www.portcommodore.com/commvex

[Justin]

Wow, the parts for doing this are prohibitively expensive now, 141 for the cga to rbg converter?  Has anyone come up with a solution that is less ridiculous?  I ran into this when poking around: http://www.ambery.com/rgbcgatovgac.html but I suspect it would require a similar mod to make it work with the RGBI input.

[commodorejohn]

No, the RGBI output on the 128 is exactly identical to the output on a CGA card; if that thing does what it's advertised to do, then it should be as simple as plugging the RGBI cable into the converter.

[maraud]

Wow, the parts for doing this are prohibitively expensive now, 141 for the cga to rbg converter?  Has anyone come up with a solution that is less ridiculous?  I ran into this when poking around: http://www.ambery.com/rgbcgatovgac.html but I suspect it would require a similar mod to make it work with the RGBI input.

I tried one of those and the output was quite poor, granted I was trying it on an LCD but it was nearly illegible.