RGB2HDMI mod for the Atari STacy

[DarkLord]

I thought I'd posted pictures here on my RGB2HDMI mod equipped STacy (I know I did at Exxos's
Atari Forums) but I guess I didn't.

Here's just a few. One interesting thing is that the RGB2HDMI mod doesn't interfere with the
external color monitor port so you can actually have -2- screens going at once.

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[DarkLord]

I had a few people ask if the RGB2HDMI mod for the ST also allowed mono (hi-res) mode. It does, and in the pictures below you can see it in action. On the ST, simply grounding pin #4 on the video port causes it to go into mono/hi-res mode (assuming your display can handle it). Adding a simple mini-toggle switch gives you the easy ability to switch back and forth between color and mono modes (after a reboot). So my STacy can now do lo-res, medium-res and hi-res. Yay!

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[DarkLord]

BTW, here is what you get if you leave your SC1224 plugged into the external color monitor port on the STacy,
while running in hi-res mode.

https://www.youtube.com/watch?v=ZwDGV5b1vrU

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[MasterOfGizmo]

Seriously? The sc1224 basically copes with the monochrome signal? It syncs horizontally and vertically and just flickers a little bit? The mono hsync is 35khz which is more than twice the 15khz it's designed for.

That's unexpected and I wonder why they didn't went the last few steps to make it fully compatible with all three modes.

[czietz]

Seriously? The sc1224 basically copes with the monochrome signal? It syncs horizontally and vertically and just flickers a little bit?

The video does not look like it's showing the SC1224 but the builtin screen of the STacy.

[MasterOfGizmo]

Then what's the relationship to the sc1224? Does an external sc1224 disturb the internal rgb2hdmi?

Do you then have two sets of RGB termination resistors which affect the signal levels in a way that the rgb2hdmi doesn't cope with?

[af0l]

BTW, here is what you get if you leave your SC1224 plugged into the external color monitor port on the STacy,
while running in hi-res mode.

https://www.youtube.com/watch?v=ZwDGV5b1vrU


Capture.JPG

A Macintosh? Nice

Anyway, I'm following your guidance, just ordered the PCB's...

[DarkLord]

Seriously? The sc1224 basically copes with the monochrome signal? It syncs horizontally and vertically and just flickers a little bit? The mono hsync is 35khz which is more than twice the 15khz it's designed for.

That's unexpected and I wonder why they didn't went the last few steps to make it fully compatible with all three modes.

Er, what I was showing is how the replacement LCD screen in the STacy itself looks when a SC1224 is plugged into the
external monitor port.

The SC1224 screen itself is blank, and that's with the SC1224 powered on or off.

Works fine though in low and medium resolution.

I'm pretty sure a SM124 hi-res monitor would work fine with the STacy in hi-res mode. I just don't have one to try out.

[DarkLord]

The video does not look like it's showing the SC1224 but the builtin screen of the STacy.

That's it.

[DarkLord]

Then what's the relationship to the sc1224? Does an external sc1224 disturb the internal rgb2hdmi?

Do you then have two sets of RGB termination resistors which affect the signal levels in a way that the rgb2hdmi doesn't cope with?

I think this is not unexpected and working exactly like it's supposed to.

STacy in low res/med res = works fine with the SC1224.

STacy in hi-res = works fine with the SM124 or other display that can handle hi res.

I've not tried it yet but I'm going to assume that my Dell 27" monitor with the VGA adapter set to hi-res would work
with the STacy in hi-res mode as well (or any res).

Does that make more sense?

[DarkLord]

A Macintosh? Nice

Anyway, I'm following your guidance, just ordered the PCB's...

Hahaha, yeah - just grab a Spectre GCR or the like and you'd be right there.

Great! I've been well pleased (and amazed) at what the RGB2HDMI mod has done
for my STacy.

Be sure and check out Derkom's "Summer STacy Project" message thread over at
Exxos's Atari Forum - he did it first (as far as I know) and I learned a lot there. It's
a big thread but well worth going through:

https://www.exxosforum.co.uk/forum/viewtopic.php?t=3009

Let us know how things go and post pictures - we love pictures!

[MasterOfGizmo]

I've not tried it yet but I'm going to assume that my Dell 27" monitor with the VGA adapter set to hi-res would work
with the STacy in hi-res mode as well (or any res).

Does that make more sense?

To be honest: not really.

The video signals are one-way out only. Despite the mono detect signal there's no way for the St to actually know what display type is connected. You are kind of overriding the mono detect in the Stacy as it's forced into mono even with the sc1224 connected. In that case the st should not be able to tell there's a sc1224 connected.

So I am wondering how the presence of the sc1224 does impact the Stacy's own mono signal.

[DarkLord]

To be honest: not really.

The video signals are one-way out only. Despite the mono detect signal there's no way for the St to actually know what display type is connected. You are kind of overriding the mono detect in the Stacy as it's forced into mono even with the sc1224 connected. In that case the st should not be able to tell there's a sc1224 connected.

So I am wondering how the presence of the sc1224 does impact the Stacy's own mono signal.

Okay, probably someone with more knowledge than me (that would be about anyone here), could explain
this better but I'm thinking what might be missing is an explanation of the STacy's external monitor port. I don't
think it's a standard ST port out in that includes a disconnect switch. I'll attach some pictures below. Look
at the white clip on top. On an unmodified STacy, when you plug the SC1224 into the external monitor port,
it disables the onboard LCD screen. With the RGB2HDMI mod in place, this white plastic clip is removed.


Here is an unmodified STacy MB showing the external monitor port:

STacy-External Monitor Port (unmodified).JPG

Here is mine, showing the clear cover, white plastic clip both removed, and a wire running from pin #4 to a
simple toggle switch, then to ground. With the toggle switch off (open), it boots up in low or med res, and
works fine with the SC1224. With the toggle switch on (closed/connected), the STacy boots up into hi-res and
the SC1224 will flash white once, then go black and stay there for that session. The onboard LCD replacement
screen shows the garbled/wobbly screen I posted.

STacy-External Monitor Port (modified).jpg

As I mentioned, maybe someone with more knowledge can step in and explain this better...