Falcon RGB or VGA?

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mrbombermillzy
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Falcon RGB or VGA?

Postby mrbombermillzy » Mon Jul 03, 2017 9:35 pm

Hi all,

Sorry if this has been discussed before, but I couldnt find any evidence of it!

Im just about to get a multisync flatscreen LCD monitor. It should be able to sync right down to ST low res (15khz).

So the question is, how does the falcon/software differentiate between RGB and VGA modes? (Surely VGA is essentially an RGB mode?)

I take it that the software would switch between a BP and chunky screen memory system, but what identifies the different modes?

Is there an xbios or cookie jar setting or something along them lines?

Many thanks as always for any info.

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dhedberg
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Re: Falcon RGB or VGA?

Postby dhedberg » Mon Jul 03, 2017 10:38 pm

It's determined by pin 18 and 19 of the monitor port. You select VGA or RGB mode by grounding the pins (pin 18 for RGB, pin 19 for VGA). To use RGB mode on your multisync monitor you need a VGA monitor adapter with an RGB/VGA switch. If you have the parts and know how to solder you can build one yourself. Otherwise you need something like this: viewtopic.php?f=27&t=31453
Daniel, New Beat - http://newbeat.atari.org

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Greenious
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Re: Falcon RGB or VGA?

Postby Greenious » Mon Jul 03, 2017 11:14 pm

mrbombermillzy wrote:So the question is, how does the falcon/software differentiate between RGB and VGA modes? (Surely VGA is essentially an RGB mode?)

I take it that the software would switch between a BP and chunky screen memory system, but what identifies the different modes?

Is there an xbios or cookie jar setting or something along them lines?

Many thanks as always for any info.


Well, technically RGB & VGA are the same in that the same 5 signals create the picture, hsync, vsync and red, green, blue.

The big difference is hsync, (and to a certain extent vsync), in what most of us call RGB mode hsync is locked at 15,75kHz which essentially makes it compatible with standard TVs and similar monitors. The only TV connector afaik that allows you to actually connect the pure RGB signal to a TV set is the SCART-connector, which from my understanding is common in europe and somewhat rare to see on US TV sets. The 2 alternative ways of connecting the F030 to a TV is the RF Antenna output or via composite sync. Obviously RGB is preferred for the picture quality. (And hence is why we call it RGB-mode, since the same also is true for ST/STE)

The cookie jar only tells you what hardware you got, specific xbios-calls depending on your hardware tells you what type monitor is connected and also let's you change resolution etc. Of course, you could also access the hardware registers directly.

A good place to start if you want to know the exact workings of this would be "The Atari Compendium", which you can find at http://dev-docs.atariforge.org/
Updated my guides as of june 28th, 2016. Check'em out and feedback!
viewtopic.php?t=5040

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mrbombermillzy
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Re: Falcon RGB or VGA?

Postby mrbombermillzy » Tue Jul 04, 2017 10:09 pm

Greenious wrote:A good place to start if you want to know the exact workings of this would be "The Atari Compendium", which you can find at http://dev-docs.atariforge.org/


Funnily enough, Ive just started reading that for the last few days (Im still on GEMDOS functions).

Ok guys, thanks for the help. It was just as I feared, with the same sort of hamstrung pin swapping like what the ST low/med<>high cable types have (i.e. requiring a switch).

So the chunky RGB is only good for PAL/15khz then? (And obviously faster than bitplaned modes for screen draw/blit operations?)

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dhedberg
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Re: Falcon RGB or VGA?

Postby dhedberg » Tue Jul 04, 2017 10:15 pm

mrbombermillzy wrote:
Greenious wrote:A good place to start if you want to know the exact workings of this would be "The Atari Compendium", which you can find at http://dev-docs.atariforge.org/


Funnily enough, Ive just started reading that for the last few days (Im still on GEMDOS functions).

Ok guys, thanks for the help. It was just as I feared, with the same sort of hamstrung pin swapping like what the ST low/med<>high cable types have (i.e. requiring a switch).

So the chunky RGB is only good for PAL/15khz then? (And obviously faster than bitplaned modes for screen draw/blit operations?)

You only need hardware for telling the Falcon whether you want a RGB video mode (15kHz) or VGA video mode.
The number of colors and the screen resolution can be set by software using OS calls or manipulating hardware registers. The 16bit TrueColor chunky pixel mode is available in both RGB and VGA video modes.
Daniel, New Beat - http://newbeat.atari.org


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