exxos's Atari, Amiga & retro forum

I have some questions about the RGBtoHDMI project (hardware which adds HDMI video output to a range of vintage computers). I intend to add it to an STe:

1) According to the official Wiki project page for RGBtoHDMI 12-bit board, it is now at version 4. But several sellers have a version 7 (CJEmicros and RetroHackShack to mention a couple).

Is this an unoffical offshoot from the official one?
Is there a website with more information?
Are there file-downloads somewhere so I can make my own?

2) As I don't have much experience with SMD components and there's so much that can go wrong with this project (also involving multiple boards) I would like to buy it (and the other boards needed for it) ready-made.
I see that several PCB-manufacturing companies also offer ready made boards and not just bare boards, one of them being PCBway.
I suppose it's also possible to upload the Gerber and BOM files to other manufacturers.
Has anyone here ordered ready made RGBtoHDMI and 12-bit Extender boards? How did they come out and how much did they cost?

3) Since there's no buffer board available for the STe I'm working on a design for that, but I'm confused about the signal pins of the RGBtoHDMI and 12-bit extender boards. I've compared several of the existing buffer boards (Atari ST, Amiga, Atari ST with no buffer etc.) and I see that the signals aren't the same.
For instance, in one design (12-bit Atari ST buffered pickup board) the R3, G3 and B3 pins all receive the Atari ST MONO signal.
In other designs the SYNC pin receives a variety of sync type signals, and a modified Amiga buffer for use with the STe has CSYNC going to the SYNC pin of the RGBtoHDMI and MONO going to the VSYNC pin.
Is this because although the RGBtoHDMI input pins have a specific signal labelling they're not fixed, but the actual signal it will carry is determined by which profile has been chosen, differing between the various vintage computer settings?

The answer to question 3 will be that ST only had a 9-bit colour and STe had 12-bit colour and so on the ST there is no R3, G3 or B3

alexh wrote: 18 Sep 2026 20:12 The answer to question 3 will be that ST only had a 9-bit colour and STe had 12-bit colour and so on the ST there is no R3, G3 or B3

Thanks for confirming :thumbup:

Would it then be safe to also assume that the reason for the different signal names (on the input pins of the RGBtoHDMI) are indeed because they're not hardwired and fixed, but re-configurable. So the signal names don't necessarily match the actual signal received. Do you agree?
For instance, comparing the STe and ST, here showing only the pins that differ for simplicity (and with pin numbers of the RGBtoHDMI input connector in paranthesis):

ST	STe	RGBtoHDMI input connector
MONO	R3	R3 (11)
MONO	G3	G3 (13)
MONO	B3	B3 (15)
HSYNC	CSYNC	SYNC (12)
VSYNC	MONO	VSYNC (14)

These topics over on AF are probably helpful to you:

Flow diagrams which help understanding of how it works with ST & STe:
https://www.atari-forum.com/viewtopic.p ... 98#p487598

MegaSTe wiring:
https://www.atari-forum.com/viewtopic.p ... 08#p488108

STe wiring:
From page 4: https://www.atari-forum.com/viewtopic.p ... 21#p420221

Some slight differences in wiring, perhaps there was an error on page 4.
From page 5: https://www.atari-forum.com/viewtopic.p ... 17#p421117

I have 5 ready built rgb2hdmi hats if you want one, PM me. They are 12 bit issue 4's.

They have had basic tests done, they boot, displays the menu etc and the CPLD was programmable via RPi.

I haven't fully tested yet but I can if you want one.

Steve wrote: 19 Sep 2026 10:35 These topics over on AF are probably helpful to you:

Flow diagrams which help understanding of how it works with ST & STe:
https://www.atari-forum.com/viewtopic.p ... 98#p487598

That's actually my own posting!
I made some diagrams when I was pretty clueless about the project (I still am, but at a lesser extent), hoping to get some comments so I could figure out the basics/get an overview.
Apparently I got it right, since you're reposting it here :lol:

I'm curently working on a buffer-board for the STe as there's no such thing available, as you can see in the diagrams.

Actually I can't take credit for the design as it's an already available 12-bit Amiga buffer board (the schematic, PCB files etc. can be downloaded from here). It's been slightly modified to work with the STe and documented here (there's a pinout error there, but the author is in the process of fixing it).

I'm working on a redesign and some smart mounting solution inside the STe.

MegaSTe wiring:
https://www.atari-forum.com/viewtopic.p ... 08#p488108

STe wiring:
From page 4: https://www.atari-forum.com/viewtopic.p ... 21#p420221

Thanks! I've read through those before, but re-read them now with "new eyes" and discovered some information that confirmed that my connections were right (particularly the quote by IanSB in that posting).

Some slight differences in wiring, perhaps there was an error on page 4.
From page 5: https://www.atari-forum.com/viewtopic.p ... 17#p421117

Yes, that's a good piece of information!
You're right about there being errors in those connections to the STe's resistors attached to the video shifter chip. I know lots of people had problems with this because the STe schematic had a different way of explaining things compared to other standard methods or something (not the first time Atari re-invented established standards), so I followed the instructions somewhere telling me to also check the resistor values from the video shifter chip as that would help determine the correct order (i.e. R0, R1, R2, R3 and similarly for the G and B lines).

So I now have the signals checked and noted from both my STe computers which matches some "corrected pinout" posting somewhere in the Atari forum. I just can't remember which one at the moment.
Someone really should write a proper user-guide/installation-guide on the RGBtoHDM for Atari ST/STe ownersI!
As someone pointed out: there are lots of cool hardware add-ons for Atari ST computers, but most of them are presented as "projects", and most people aren't interested in buying into a project, but rather a ready to use solution.
For the RGBtoHDMI you really have to (in my experience anyway) read through numerous threads to connect the dots, and even then there's a lot fo guesswork :shock:

@Pacman I managed to install RGBtoHDMI in two of my STe's following those spotty forum posts, but I am no expert. You probably know more about it than me now.

In terms of making a standard installation method, perhaps @exxos may be interested in modifying his STe DAC upgrade board to being more of a RGBtHDMI pick-up board: https://www.exxosforum.co.uk/atari/last ... /index.htm

I assume it's tagging on to the same signals required by the DAC?

Pacman wrote: 18 Sep 2026 21:53 Would it then be safe to also assume that the reason for the different signal names (on the input pins of the RGBtoHDMI) are indeed because they're not hardwired and fixed, but re-configurable.

Mono will be low in colour mode and for the standard ST will hold R3, B3 and G3 low which converts the 9-bit Atari ST input into a compatible 12-bit value for the 12-bit pickup board. (In Mono mode, when the MONO pin is high, the Pi doesn't look at R3/B3/G3)

This is the VHDL for the latest 12-bit pickup CPLD

https://github.com/hoglet67/RGBtoHDMI/b ... oHDMI.vhdl

You can see that it has three inputs "VSYNC, CSYNC and VERSION". VERSION (which is probably user controlled) changes the behaviour of VSYNC or CSYNC. I think it implies you have to switch (but it might be automatic) between ST and STe sync modes.

The design intent for wiring MONO to the VSYNC pin in the STe isn't 100% clear to me but I'm sure if I looked long enough I could work it out.

Steve wrote: 23 Sep 2026 14:15 I assume it's tagging on to the same signals required by the DAC?

It is.

My own resistor notes, which I assume echo the threads above:


It does mean a bit of a rat's nest of wires and I'd love if it was cleaner. I'm always paranoid that I'll have a weak solder joint in that mix. My kingdom for something more stable!

Is BLANK signal not needed on the STe RGB2HDMI board?