8-bit Computer TV Channel Use

Mark J. Blair nf6x at nf6x.net
Sat May 23 11:33:53 CDT 2015

> On May 23, 2015, at 08:35, Chris Osborn <fozztexx at fozztexx.com> wrote:
> On May 23, 2015, at 8:24 AM, Mark J. Blair <nf6x at nf6x.net> wrote:
>> In the middle will be some FPGA to perform any necessary magic. I've been looking at a prohibitively expensive ($115) one that has enough dual-port RAM blocks to support a frame buffer.
> Are you on the CoCo mailing list? Have you seen the RGB2VGA by Luis Antoniosi (CoCoDemus)? I know at one point he had been tinkering with making it support composite from the Apple II. It’s semi open-source, I think there are 2 versions and the latest version is currently all closed source.
> https://sites.google.com/site/tandycocoloco/rgb2vga

I'm on the list, but it's so high-volume that I rarely read it. I'll look at the RGB2VGA board to see if I might learn anything from it. His mention of a line buffer is already my "Oh, duh!" moment about how to use cheaper external SDRAM instead of on-FPGA dual-port memories for the frame buffer. The dual-port memories are very convenient, but having enough to form a frame buffer pushes the design up into over-$100 FPGAs.

> On May 23, 2015, at 08:36, Fred Cisin <cisin at xenosoft.com> wrote:
> Where are you located?
> Would you like some of the REAL monitors?

I'm in Riverside, CA, but I already have enough real monitors. :)

> On May 23, 2015, at 08:45, wulfman <wulfman at wulfman.com> wrote:
> maybe this will do ?
> http://www.ebay.com/itm/GBS-8220-RGB-CGA-EGA-YUV-to-VGA-ARCADE-VIDEO-CONVERTER-BOARD-Latest-Software-/120967105011?ssPageName=ADME:B:FSEL:US:1123

It's similar, but probably not right for this application. It outputs VGA, which is already obsolescent, at a maximum resolution of 1360x768. The goal of this project is to drive modern 16:9 monitors and TVs at 1080p, over HDMI. I believe that board on eBay is intended for replacing monitors in coin-op video games, which generally have very different video hardware compared to vintage 8-bit home computers. Has anybody tried this board with home computers that are known to be troublesome with modern displays? I'm at least interested in seeing how they got the price down to $40, and whether anything in their solution might be usable for this application without being able to read Chinese datasheets. :)

On May 23, 2015, at 08:59, Jochen Kunz <jkunz at unixag-kl.fh-kl.de> wrote:

> Am 23.05.15 um 17:24 schrieb Mark J. Blair:
>> In the middle will be some FPGA to perform any necessary magic.
> What about the analogy of Software Defined Radio:
> Use only as much electronics as minimal necessary to get the input
> signal digitized by a high speed ADC.

I initially considered using SDR techniques for the TV demodulation. Using an off-the-shelf TV tuner IC would probably be much cheaper than building an appropriate RF front end from scratch, though if it outputs an IF instead of baseband then SDR techniques might still be the cheapest way to extract the video baseband, since the design would have a couple of ADCs in it in any case to handle Y/C from a C64. Don't want the ADCs to be too expensive, though...

> Maybe some cheap DVB-T USB thing
> can be abused for the ADC part. Do the processing in software on a
> "normal" computer. (PeeCee, some ARM single board thing.)
> Disadvantage:
> - needs extra PeeCee / ARM-SBC for processing.
> - No obscure FPGA magic needed.

+ Latency

I think that's a non-starter due to latency. I can't imagine the overall latency being lower than several video frames, and that would be a killer for games. If it could work with sufficiently low latency, then using something like a Raspberry Pi or Beaglebone Black instead of a PC could lower the price and make it more stand-aloney.

Mark J. Blair, NF6X <nf6x at nf6x.net>

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