Connect with us

An IC for generating composite video signals

Discussion in 'General Electronics Discussion' started by Volter, Jul 23, 2016.

Scroll to continue with content
  1. Volter


    Jul 23, 2016
    Hello, first post! :D

    I have recently built my own Z80 computer and now would like to allow the computer to print graphics and text to a TV/Screen.

    My question is: is there a simple standalone IC that can read bitmaps from RAM and produce a composite (PAL) signal that can then be fed to a display?

    The main limitation I have is that I don't want to use microcontrollers/microprocessors like Arduino, to be more clear I would only want to use "vintage" IC's.

    Hope this is not to much of a silly question.
  2. AnalogKid


    Jun 10, 2015
    It's an ok question, just 20 years late. Most of the analog video CG chips are out of production. You can search for old datasheets and app notes from companies like Mostek, National, SGS, etc.. Also, this and other fora have a flea market section for buy/sell/swap. You might find someone with a few chips laying around from a past project.

    Volter likes this.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    It's a wunnerful question, not a silly question at all for those interested in vintage computers! You could start by trying to find this obsolete Analog Devices AD722 encoder. Good luck with that. I wasn't able to find any for sale anywhere, but I didn't try eBay. Caveat emptor there.

    You would also have to add the readout circuitry to retrieve RGB pixels from the RAM and send them at the proper video rate to the encoder. We used to parallel-load shift registers with pixels and shift the bits out at video rates to make composite video, but that was, like... in the 1970s. Most of those parts are obsolete too. Matter of fact, I once bread-boarded an NTSC encoder back then using standard TTL components. A few months after I finished that project, ICs that did the same thing became available. <sigh> It was a good learning experience though. Microprocessors were new then and we had begun playing around with Intel 8080s at the time.

    Wouldn't you rather buy a nice new computer? I hear there have been some improvements since the Z80 was released for production. Some of the newer models can be programmed to play games like PACMAN or PONG, and many have been recently built into new arcade games that emulate games of that era when arcade games were built around the Z80 and a real color CRT (vacuum tube type with shadow mask). Or maybe you could find a used Commodore 64, or something similar like an Atari game console, and hack its video converter and RAM. Might even find the parts you need inside one of those oldie goldie PCs... TRS-80 perhaps? Be sure to wear protective clothing and a filter mask when diving around in landfills. Estate auctions would be a better place to start looking. Good hunting!

    Now that you have a working Z80-based personal computer, what are you going to do with it? Add a color monitor fer sure. Maybe a Kansas City or even a Tarbell tape interface for loading and storing programs? Hows about a 5-1/4" floppy drive? A vintage 100 MB hard disk drive too?:D
    Volter likes this.
  4. evanpnz


    Feb 19, 2013
    I think the Z80 itself will do the job nicely. I believe the Commodore 64 used the processor to generate video and did all it's other housekeeping, running Basic etc. during the vertical blanking interval. If you want source code, or at least a basic idea of how it was done, an amateur radio TV signal generator called PIC-Dream should still be floating around the web archives somewhere...
    hevans1944 likes this.


    Mar 28, 2011
    The original Tandy TRS80 had all that's required built in, including a RF modulator to be used with ordinary TVs, this is probably the best bet.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day