C128 RGBI Electrical Characteristics
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From: JohnH. on 5 Oct 2006 11:22 I'm looking for a detailed description of the electrical characteristics of the C128s RGBI output. A friend of mine is an electronics engineer for Hamilton Beach. In an exchange of favors he has agreed to help me build a color interface between C128 80 column RGBI output and a modern flat panel monitor. I'm not sure if the output would be VGA, S-Video or component video at this point. The starting point is obviously a fundamental understanding of RGBI output. In my web searches I recall seeing a document that went into the C128's RBI output in great detail showing voltage levels and timing. I can't find that web site again. I'm beginning to doubt my memory. Has anybody seen, or does anybody have a document like this? Thanks, John
From: a7yvm109gf5d1 on 5 Oct 2006 13:05 JohnH. wrote: > I'm looking for a detailed description of the electrical > characteristics of the C128s RGBI output. A friend of mine is an > electronics engineer for Hamilton Beach. In an exchange of favors he > has agreed to help me build a color interface between C128 80 column > RGBI output and a modern flat panel monitor. It's just a 74LS245. Look here http://www.dfpresource.org/ How much longer can you wait? > I'm not sure if the output would be VGA, S-Video or component video > at this point. The starting point is obviously a fundamental > understanding of RGBI output. There's not that much to understand. There's a Hsynch, a Vsync and 4 bits that describe the color of each pixel on a line. > In my web searches I recall seeing a document that went into the > C128's RBI output in great detail showing voltage levels and timing. > I can't find that web site again. I'm beginning to doubt my > memory. Has anybody seen, or does anybody have a document like this? > > Thanks, > John You're better off reading the specs on the timing of the VDC to understand the signal. I just bought a 128 prg reference guide from eBay to help me do just that, even though I already have a pretty complete Compute's Gazette Mapping the 128 here. Electrically, there's not much to it. TTL levels. The basic thing you're likely to need is a AL250 or AL251 chip. You can then take the upscanned digital outputs to a DVI transmitter chip, or be happy with analog VGA. The AL250 chips are like 10$ each in small qties. There are some people in this group that insist that a device to convert RGBI to VGA already exists made by Extron. This is false and I'm still waiting for a picture of the working setup. The other person thinks you can just program the VDC to output 31KHz Hsync when every test I've made show the VDC stops at about 21KHz Hsync. Ignore these people.
From: a7yvm109gf5d1 on 5 Oct 2006 14:32 JohnH. wrote: > I'm looking for a detailed description of the electrical > characteristics of the C128s RGBI output. A friend of mine is an > electronics engineer for Hamilton Beach. In an exchange of favors he > has agreed to help me build a color interface between C128 80 column > RGBI output and a modern flat panel monitor. > > I'm not sure if the output would be VGA, S-Video or component video > at this point. The starting point is obviously a fundamental > understanding of RGBI output. > > In my web searches I recall seeing a document that went into the > C128's RBI output in great detail showing voltage levels and timing. > I can't find that web site again. I'm beginning to doubt my > memory. Has anybody seen, or does anybody have a document like this? > > Thanks, > John Oh yeah, what's really important is understanding the palette http://en.wikipedia.org/wiki/List_of_palettes There is still some confusion in my mind as to wether the 128 uses the "real" RGBI colors or if the C= monitors used the same trick the CGA monitors used to get brown. http://en.wikipedia.org/wiki/Color_Graphics_Adapter Honestly, my 1080 is so out of whack I can't tell what the colors "really" are supposed to look like on a C= monitor. If you want, I can send your friend the spreadsheet I'm using to develop my hardware. email me.
From: MagerValp on 5 Oct 2006 15:08 >>>>> "J" == JohnH <john(a)jrcc.net> writes: J> I'm looking for a detailed description of the electrical J> characteristics of the C128s RGBI output. A friend of mine is an J> electronics engineer for Hamilton Beach. In an exchange of favors J> he has agreed to help me build a color interface between C128 80 J> column RGBI output and a modern flat panel monitor. Nice :) J> I'm not sure if the output would be VGA, S-Video or component video J> at this point. RGBI -> Component video would require the least work, so that's probably a good starting point. Schematics for turning RGBI into analog RGB can be found in a couple of places: http://www.softwolves.pp.se/cbm/maskinvara/scart.en.html http://www.zimmers.net/anonftp/pub/cbm/documents/cables/128-videocable.txt J> The starting point is obviously a fundamental understanding of RGBI J> output. Fortunately it's dead simple. The signals are TTL level, sync frequency matches NTSC or PAL timing. AFAIK the sync can be wired without conversion to a SCART connector. Scart to component adapters can be found in HiFi stores. -- ___ . . . . . + . . o _|___|_ + . + . + . Per Olofsson, arkadspelare o-o . . . o + MagerValp(a)cling.gu.se - + + . http://www.cling.gu.se/~cl3polof/
From: Jukka Aho on 5 Oct 2006 16:48
a7yvm109gf5d1(a)netzero.com wrote: >> RGBI -> Component video would require the least work, so that's > I think you'll find that's completely untrue. I eagerly await a > simple circuit to take 16MHz dot clock video and encode color > unto a 3.58MHz colorburst. It's not trivial, not by a long shot. What are you on about? The previous poster talked about component video, not composite video. Component video does not have a "colorburst". > Debatable, the exact frequency of color NTSC is derived from the > colorburst frequency. There is only *one* _true_ color NTSC hsync > frequency. The 128 is close but not the same. Monitors work fine > because they can accomodate some variation in the sync, but a > color TV will expect signals at the right place, esp the colorburst. (Practically) all European tv sets have the ubiquitous SCART connector with its RGB input pins, so only a fool would fiddle with the composite or s-video signals here when a better option is available. The simple SCART cable described in the links that MagerValp already mentioned should suffice. The situation on your side of the pond is probably worse in that respect, since tv sets there don't come with RGB inputs. But I believe modern NTSC tv sets - at least the larger ones - usually come with YPrPb component inputs for DVD players and game consoles. This should be almost as good. I'm not an electronics buff, but I've been told that converting from analog RGB to YPrPb is a relatively trivial matrixing job. Here's a device that does exactly that, and it doesn't look too complicated: <http://www.siliconchip.com.au/cms/A_102648/article.html> As you say, converting the C128's RGBI signal to composite or s-video signal is probably a harder problem - but who really cares about composite or s-video signal if you can use European-style SCART RGB or American-style component (YPbPr) signal? And why are you bringing obsolete composite or s-video signals and their color burst timing problems into this discussion at all when the original poster doesn't even want to use a tv set but a flat-panel PC monitor? -- znark |