DigicoolThings Forum

Earlier, I posted an article (and video) on my TMS9929A Video Display Processor (VDP) rediscovery. This included designing an alternative Retro VRAM solution, which I then implemented as a breadboard prototype and verified successful operation.

Having built an MECB backplane, and my first actual MECB card (a Prototype card), and also having proved the PLD based address decoding logic, it then seemed like a good time to implement my TMS9929A based VDP circuit design onto a PCB, as my first MECB Video Card.

See the full post and video (plus follow-up video), here: Minimalist Europe Card Bus (MECB) – TMS9929A / TMS9928A VDP RGBS Video Card

More recently, someone mentioned that they were planning on using a TMS9918 VDP chip, with the MECB TMS VDP Display Card.

This prompted me to update the MECB VDP Display Card design to v2.0, to also add support for the TMS9918A variant. So now, all variants are catered for!

See the v2.0 update post and video here: Minimalist Europe Card Bus (MECB) – TMS992x or TMS9918 VDP Display Card – v2.0 Update!

So, this v2.0 TMS VDP Card now supports: Update: I've now finally tried a TMS9928A on the VDP Display Card, which provides a really clean and nicely framed 60Hz RGB Video on my small workbench monitor. Very happy with the result, which you can see here: Minimalist Europe Card Bus (MECB) - A TMS9928A on the VDP Display Card!

Just updated this topic to now reflect v2.0, and I also added a link (above) to the latest blog post & video covering the v2.0 Update!

Hi Greg,

Well I experimented with putting a TMS9118 on to your Video card. Here it is: Yeah, it was a bit of a bodge job. Kinda worked, the background colors cycled but the text was there
but a wash out. So I made my own pcb and while I was there I added a YM2413 sound chip to it:
Well, this worked a little better, at least I could SEE the text on screen. Unfortunately there was a still
a lot of noise ie the text was "sparkly" and it was best to have text and background colors close to each
other, for example light green background and dark green text. The layout of the pcb wasn't exactly optimal
so I've redone it and am waiting for the pcbs to arrive - here's the 3d render:
Well it looks like I can have only 3 images (via attachment) per post and I've got six! So I've cut off the bottom
half of this post and added a "part 2" post. See ya the.re

Editor wrote: ↑Fri May 03, 2024 7:33 pm Just updated this topic to now reflect v2.0, and I also added a link (above) to the latest blog post & video covering the v2.0 Update!

Nicely done. I see the old and new designs have a different port placement on the PCB, am I right?

Also, I have a number of retro CRT monitors that have Digital RGB standard connectors, now I did try to have these old computers I have, use a conversion cable to a standard 15 pin VGA using 157ohm resistors on the R,G and B lines, but not many modern monitors (or even most CRTs for that matter) support the 15Khz output, and I'm stuck using either composite, or back using these Digital RGB monitors - so since I have a number of these low Khz monitors on hand anyway, would it be a huge stretch to convert any of the TMS series video chips to use these Digital RGB monitors?

lenzjo wrote: ↑Mon May 06, 2024 12:51 pm ... Well I experimented with putting a TMS9118 on to your Video card. Here it is: ...

You have been busy!

Firstly, let me say how awesome it is to see your post! You really have dived right-in with what my core intention was, with documenting the MECB system.
That is, to provide a modern standard framework for re-discovering our early days of building our own 8-bit creations!

Next, we need to get your awesome images visible to all! (See my reply on your intro post).

My first 6502 MECB Card prototype PCB has been done for a while now, but has unfortunately just been sitting in its PCB delivery box waiting for me to get to it. I seem to be mostly slowed down by other "life" projects, other MECB Card updates, and the time it takes me to make a video! LOL

What you have achieved so far with MECB is like a breath of fresh air, and very inspiring! Keep it up!

lenzjo wrote: ↑Mon May 06, 2024 12:51 pm Future plans: I have a couple of mc6828s from way back in the eighties. Always wanted to use them but never
got around to it and largely forgot about them. All this 6809 stuff refreshed my memory about them and so I'm
gonna have a go at making a priority interrupt card. I've also got some 6845 and 6545 vdu chips. If the tms9118
display doesn't improve on the next card I may have a go using one of them. I would like some form of mass
storage so I am looking into that. In the meantime I'm writing a monitor for the 6502 board.

I've never played with the 6828 PIC, so I'm keen to see what you come up with.

Yes, the 6809 was always my favourite 8-bit to program with it's more complete & powerful ISA. Also, although I enjoyed coding on the 6502 (back in the day), because I had played with the 6809 first I was kind of spoiled and therefore found some of the necessary 6502 codlng "workarounds" a little frustrating (as in, taking focus away from the core programming function I was working on).

Being originally a Motorola fan, I do have 6845 and 6847 video chips in my parts storage, and these have also been in the back of my mind for some future MECB card experimentation.

bugeyedcreepy wrote: ↑Mon May 06, 2024 1:42 pm Nicely done. I see the old and new designs have a different port placement on the PCB, am I right?

No changes to the port placement. The only port change was to the silkscreen labeling of the MD2 Video Output, which I changed from "RGBS" to "Video", as a more general term (to allow for either). The added TMS9918A Composite Video circuitry, just hooks into the existing port routing.

bugeyedcreepy wrote: ↑Mon May 06, 2024 1:42 pm Also, I have a number of retro CRT monitors that have Digital RGB standard connectors, now I did try to have these old computers I have, use a conversion cable to a standard 15 pin VGA using 157ohm resistors on the R,G and B lines, but not many modern monitors (or even most CRTs for that matter) support the 15Khz output, and I'm stuck using either composite, or back using these Digital RGB monitors - so since I have a number of these low Khz monitors on hand anyway, would it be a huge stretch to convert any of the TMS series video chips to use these Digital RGB monitors?

The only "digital" RGB CRT I recall owning (for a short while) would have been a CGA (or EGA?) colour monitor, before VGA took over.

I'd assume the best approach to make these monitors usable for Retro RGB Standard Defintion video use, would be to convert the monitor inputs to support standard 1V peak analog RGB input levels.

I'd expect the Digital RGB inputs probably convert the input signals to normal RGB video levels for further processing, so hopefully you can just identify this point on the input circuit to hook-up a normal RGB level video signal? A service manual / schematics would certainly help here. Perhaps a google for your monitor, will find more information on this?

I haven't ever done this conversion myself, so I can't really advise any furter on this. But I'm sure, that once done, the monitors would make for really awesome image quality retro monitors for Standard Defintion video signals in the clean RGB Component Video format!

Here's the rest of my post:


While I'm here I may as well show you other stuff. Being an ancient 6502er, I've put together a 6502 board. Based
heavily on your 6809 for layout here it is:
It has selectable clk speed (1, 2, 4, 8 and 16Mhz) can accept either the wdc 6502 or a NMOS one, I'm just
waiting for the SRAM so I can test it.

The last toy to share is my backplane. I'm not really a fan of all kinds of cables hanging of the top of the
cards. So I've moved as much as I can onto the backplane.For power I kept only the 2.1mm connector, to
keep power input options open I use the adapter below. With it I can still have the choice of 2.1mm, bare cables
or USB.
I kept the power switch but added an LED to show it's status. As I/we are experimenting with diff. cpus I put the
reset circuitry (DS1813 and btn) on here as well. For serial i/o I added a USB mini B with a cp2102
to do USB to serial conversion and there to LEDs to show Tx and Rx activity. Along the top I've put PS2 keybd
socket and a composite video output on the backplane and while I was in layout mode I added a couple more
DIN 41612 sockets. Here it is:
Future plans: I have a couple of mc6828s from way back in the eighties. Always wanted to use them but never
got around to it and largely forgot about them. All this 6809 stuff refreshed my memory about them and so I'm
gonna have a go at making a priority interrupt card. I've also got some 6845 and 6545 vdu chips. If the tms9118
display doesn't improve on the next card I may have a go using one of them. I would like some form of mass
storage so I am looking into that. In the meantime I'm writing a monitor for the 6502 board.

lenzjo wrote: ↑Tue May 07, 2024 8:05 am Here's the rest of my post: ...

Hi Clive,

What you've built so far is awesome.

For your Backplane, I'm assuming the middle 4 connectors are standard MECB (for any MECB Cards), and just the two labeled straight female connectors at each end (i.e. connectors 1 and 6) have the custom connections for each external connector?

Okay, my next big question is: Are you planning on sharing your Card / Backplane designs with others, so that others who are interested in them can also build their own too? e.g. shared gerbers via Gihub etc. (when you're ready to share them, of course).

If so, you could create a seperate Forum discussion topic for each Card design that you're happy to share, or to further discuss the design details (in this Minimalist Europe Card Bus subforum).
I could then add your creations to the table in the MECB Roadmap / Index, featuring links to each of your Card topics.

Just a thought... over to you.

lenzjo wrote: ↑Tue May 07, 2024 8:05 am I would like some form of mass
storage so I am looking into that

I'm part way through a compact flash attempt since I have hundreds of them from old cisco devices - I have no idea what I'm doing though. If you know much about anything along those lines, I'd love to hear about it...

Editor wrote: ↑Tue May 07, 2024 10:07 pm What you've built so far is awesome.

Your too kind...

Editor wrote: ↑Tue May 07, 2024 10:07 pm For your Backplane, I'm assuming the middle 4 connectors are standard MECB (for any MECB Cards), and just the two labeled straight female connectors at each end (i.e. connectors 1 and 6) have the custom connections for each external connector?

Close.. The I/O board can go in slot 1 or 2, and the VDP can go in slot 5 or 6. I did debate about the lines run the full length of the backplane, but I felt it was better (esp for the the VDP) to limit the path length.

Editor wrote: ↑Tue May 07, 2024 10:07 pm Okay, my next big question is: Are you planning on sharing your Card / Backplane designs with others, so that others who are interested in them can also build their own too? e.g. shared gerbers via Gihub etc. (when you're ready to share them, of course).

Of course I am Only the backplane is "finished" so fa,r and ready for public consumption. It's just finding the time. Some pcbs arrived on Friday and I've been soldering and writing firmware since then hence the radio-silence. The updated VDP card is put together and I've been writing the screen routines for the Text Mode.

Editor wrote: ↑Tue May 07, 2024 10:07 pm If so, you could create a seperate Forum discussion topic for each Card design that you're happy to share, or to further discuss the design details (in this Minimalist Europe Card Bus subforum).
I could then add your creations to the table in the MECB Roadmap / Index, featuring links to each of your Card topics.

Can do, again it;s finding the time...