8-bit Computer TV Channel Use

Mark J. Blair nf6x at nf6x.net
Mon May 25 12:03:38 CDT 2015

> On May 25, 2015, at 05:46, Alan Hightower <alan at alanlee.org> wrote:
> OMG, stop.

No, thank you. You are not compelled to participate if the idea offends you.

> Google "Composite to HDMI" and you will find hundreds of low
> cost boxes that do this.

And as has been already discussed, none of them is universal, all of them are quirky, and many/most of them work poorly.

> Hopefully one of them will work for you.

If you would like to purchase hundreds of converters to catalog which ones work with each screwball vintage computer, I will welcome the data.

> I was
> going to do your idea for C64s long ago until I realized there's no way
> I can do it nearly as cheap as Mr. Wong in his apartment in Shenzhen,
> Guangdong.

It would be delightful if Mr. Wong saw fit to make the cheap converter that many collectors are asking for, but anecdotal evidence suggests that he has not yet made it. As Mr. Hirsch posted:

>> On May 23, 2015, at 10:28, Steven Hirsch <snhirsch at gmail.com> wrote:
>> I own one of just about every commercially available (and hobby) converters and precisely none of them provides a universal solution. Some give great displays from an Amiga and suck for anything else.  Of my two (pricey) CVP CM-345S converters, only one provides useable display from an Apple IIGS.  My GBBS-8220 can occasionally be coaxed into giving a solid display from a Color Computer 3.  The list goes on...

Our friend Mr. Wong is very good at making inexpensive products using off-the-shelf commercial chips that were designed for use in mass-market products (particularly including zillions of them that are difficult to impossible to buy without learning to speak Chinese and heading over to Shenzen), but I get the impression that handling misbehaving 80's analog video outputs for modern displays in a clean, multi-standard way has been a requirement that's much too niche for the commercial market to address with cheap ASICs. But if I'm wrong about that, I'll be happy to buy a $15 converter or three that just work!

> However if you really want to pursue your idea "because it is fun for
> you", I suggest looking at the Lattice XO2 Control Development Kit
> (novel idea of OpenLDI in/out + LPDDR2), the Digilent Atlys board
> (Spartan 6 + dual direct TMDS in&out), or NeTV (Marvell SoC + Spartan 6
> w/ dual direct TMDS) as starting points.

Thanks for the suggestions, and I'll look at them. I'm leaning towards considering the least expensive Xilinx Zynq chip at the moment, because I am intrigued by the idea of using the CPU core to analyze an unknown incoming signal to see how "automagic" it could be made. I certainly don't expect 100% success, and some user configurability is certainly needed, but it would be pretty neat if the user could plug in an arbitrary computer, and the box could determine "oh, this is PAL on UK channel xx", "this looks like an Apple ][ in monochrome 80 column mode", etc.

> You don't even need a full frame buffer if you need to scale. If the
> frame rates match, you can just store one line if you need to horizontal
> stretch and/or line-double, or three lines if you want to perform
> multi-tap vertical scaling. All HDMI TVs (at least in North America)
> support 480i however you generally have to pixel double per the CEA-861
> standard to have enough clocks in the HBI/VBI to pass audio.

True, but one of my primary goals is to support vintage computers from countries other than the US, so I cannot rely on frame rates matching. I expect that I will have some learning curve to get over to obtain clean scan rate conversion.

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

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