C128 RGBI Electrical Characteristics
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From: LocalH on 9 Oct 2006 01:16 silverdr wrote: > Joseph Fenn wrote: > >>> >>> J> BTW, the 2407WFP is an awesome monitor. It allows me to do split >>> J> screen and picture-in-picture views of 8-bits on the composite or >>> J> S-Video ports and my Wintel PC on the VGA port. This is useful for >>> J> referencing online docs while working with the 8-bit. >>> >>> Ooh, nice. >> >> No way can it be done with NTSC protocol. At least no one has >> succeeded to date! Pal yes it exists. NTSC negativeo > > Hm, interesting. Why? Both types of signals have to get very much > "refactored" before they can get displayed on the LCD so one may wonder > what's wrong with NTSC in that case. Don't pay attention to him. He's spammed eight times across four threads already saying the same thing - "It's never been done for NTSC". What type of signal does a VDC in a PAL 128 output? PAL or NTSC? (Yes, I know, it's not actually "PAL" or "NTSC", I'm referring to the VBI rate) Are there thick vertical borders, similar to what you might see with an 8- or 16-bit game console? If not, then it's likely an NTSC-equivalent signal anyway. I can't find any documentation either way, so I'm beginning to doubt that there is any difference in VDC output between PAL and NTSC C128s.
From: Kelli Halliburton on 14 Oct 2006 13:36 On Thu, 05 Oct 2006 10:05:27 -0700, a7yvm109gf5d1 wrote: > 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. Salvage! The output of the 128's VDC was essentially CGA at the RGB output level. A lot of CGA cards had a composite video connector, thus they had a video modulator on the card that could be hooked to the RGB output of the CGA chip. If you can find one of those old cards, or find the composite video circuitry from a PCjr or Tandy 1000 motherboard, you're in business.
From: John Heitmuller on 14 Oct 2006 20:10
Kelli Halliburton wrote: > Salvage! > > The output of the 128's VDC was essentially CGA at the RGB output level. A > lot of CGA cards had a composite video connector, thus they had a video > modulator on the card that could be hooked to the RGB output of the CGA > chip. If you can find one of those old cards, or find the composite video > circuitry from a PCjr or Tandy 1000 motherboard, you're in business. There are a few CGA cards, PCjrs and Tandy 1000 on ebay. This seems like an interesesting idea. But, frankly it is beyond my current capability. Have you actually done this? Thanks for the idea, John |