The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby czietz » Wed Aug 01, 2018 4:49 pm

OK, I figured out what happens with the STE. There, in mono mode, the GSTMCU will not generate a BLANK(ing) signal, since that is not needed in monochrome mode anyway. Hence, if we only switch the Shifter to color, /BLANK will be constantly asserted and thus the RGB outputs are blanked. This is why one only gets a black screen, not even background color.

Unfortunately, this means that unless there is way to force the GSTMCU to always generate /BLANK or to force the Shifter to ignore it -- and I don't think there is --, this 400 lines color mode will not display anything in an STE without HW modification. :(

This also explains why it works the other way around. If the GSTMCU is in color but the Shifter is in mono, the Shifter will simply ignore the then superfluous blanking signal.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby thomas3 » Wed Aug 01, 2018 5:48 pm

Regardless, this is as cool af. People shouldn't be deterred - let's rock some stf only effects like it's 1989 xD

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ryan » Wed Aug 01, 2018 6:34 pm

It's absolutely awesome, and given that there are far fewer STes than STfs out there, really not that big of a deal if it's not supported on the STe.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby Cyprian » Wed Aug 01, 2018 6:41 pm

czietz wrote:Unfortunately, this means that unless there is way to force the GSTMCU to always generate /BLANK or to force the Shifter to ignore it -- and I don't think there is --, this 400 lines color mode will not display anything in an STE without HW modification. :(

until somebody breaks it, as it was done with borders...
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby arf » Wed Aug 01, 2018 6:53 pm

BlankVector wrote:czietz, you are a genius 8)
It is incredible that no one has found that for 33 years...


Congrats from me, too!

BlankVector wrote:This opens the door to a whole new generation of demo effects. I'm sure amazing new prods will appear shortly.


And/or a way to make use of that screen estate in GEM. BrutalOverscanInSoftware ;)

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ryan » Wed Aug 01, 2018 7:06 pm

I'm sure EmuTOS could be hacked up to get VDI to render to it. But aspect ratio of 320x400 would look pretty strange. I suppose one could use the 8x16 font with it, though.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ube » Wed Aug 01, 2018 7:17 pm

evil wrote:The STe have a VGA-adapter that can be switched between colour and mono then sent to OSSC on to a HDMI-screen. The OSSC nicely display the ST output frequencies and that matches what can be expected.


You're not using my ubeswitch are you? It won't work with this mode..
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby czietz » Wed Aug 01, 2018 7:44 pm

ryan wrote:I'm sure EmuTOS could be hacked up to get VDI to render to it.


It certainly can be. This is EmuTOS in 320x400x4 colors:
emutos_320_400_4colors_.jpg


(160x400 is too small however to display the Desktop.)
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby Cyprian » Wed Aug 01, 2018 7:49 pm

what about EmuTOS 1280x400 interlace
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby BlankVector » Wed Aug 01, 2018 8:24 pm

czietz wrote:It certainly can be. This is EmuTOS in 320x400x4 colors:

Oh, brilliant :cheers:
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby evil » Wed Aug 01, 2018 8:25 pm

ube wrote:
evil wrote:The STe have a VGA-adapter that can be switched between colour and mono then sent to OSSC on to a HDMI-screen. The OSSC nicely display the ST output frequencies and that matches what can be expected.


You're not using my ubeswitch are you? It won't work with this mode..


No, I'm using the MCSWITCH by Olivier Gossuin.
http://www.gossuin.be/index.php/shop

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby mlynn1974 » Wed Aug 01, 2018 8:44 pm

Amazing discovery!! So just to get this right, you need a RGB->VGA adaptor and it displays 320*200 in 2 bitplanes (4 colours?)
It would be interesting to see Oxygene's Bob demo running in that resolution. 4 colours would mean just the Bobs - not the background obviously.
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby thomas3 » Wed Aug 01, 2018 8:54 pm

mlynn1974 wrote:Amazing discovery!! So just to get this right, you need a RGB->VGA adaptor and it displays 320*200 in 2 bitplanes (4 colours?)
It would be interesting to see Oxygene's Bob demo running in that resolution. 4 colours would mean just the Bobs - not the background obviously.


Presumably, you'd get 16 pixels of bitplanes 1+2, then 16 of 3+4, then 16 of 1+2, etc etc...?

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ijor » Wed Aug 01, 2018 8:56 pm

czietz wrote:OK, I figured out what happens with the STE. There, in mono mode, the GSTMCU will not generate a BLANK(ing) signal, since that is not needed in monochrome mode anyway. Hence, if we only switch the Shifter to color, /BLANK will be constantly asserted and thus the RGB outputs are blanked. This is why one only gets a black screen, not even background color.


What a pitty.

The STf version of GLUE still cares to generate blank pulses in monochrome, even when it is really not used. I remember Troed "complaining" about that some time ago (yeah, I know you wasn't really complaining) and wondering why the hell GLUE bothers doing that. This is why! LOL

We are indeed very lucky that at least it works on the ST. Actually we are unbelievable lucky that so many tricks do work. I was thinking about that with the issue that Alien's 4-bit sync scroll doesn't work on some SHIFTER versions. The timing is so tight that we are very lucky it still works in the more common SHIFTER version. It's about the same for most other overscan and sync scroll tricks.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby czietz » Wed Aug 01, 2018 8:57 pm

mlynn1974 wrote:Amazing discovery!! So just to get this right, you need a RGB->VGA adaptor and it displays 320*200 in 2 bitplanes (4 colours?)


320x400 in 2 bitplanes.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ryan » Wed Aug 01, 2018 9:05 pm

czietz wrote:
ryan wrote:I'm sure EmuTOS could be hacked up to get VDI to render to it.


It certainly can be. This is EmuTOS in 320x400x4 colors:
emutos_320_400_4colors_.jpg

(160x400 is too small however to display the Desktop.)


Neat. Needs taller icons, too I guess. But great work.

So basically it's just med-res 'turned around'.

The 160x400 I can see being useful for vertical scroller type games.

Can a 640x100 with 4 bits depth be done?

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby joska » Wed Aug 01, 2018 10:46 pm

Cyprian wrote:what about EmuTOS 1280x400 interlace


Interlace on the ST means two different framebuffers for the odd and even frames, I'm quite sure that EmuTOS' VDI isn't up to that without significant changes.
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby Cyprian » Thu Aug 02, 2018 7:46 am

joska wrote:
Cyprian wrote:what about EmuTOS 1280x400 interlace


Interlace on the ST means two different framebuffers for the odd and even frames, I'm quite sure that EmuTOS' VDI isn't up to that without significant changes.

yep, it would be a challenge in case of ST.
But STE has virtual screen ability, and if I'm not wrong can shows Mono in color mode
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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby arcx » Thu Aug 02, 2018 12:14 pm

All these years. Such a find. ( What have we still not found ?! )

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby troed » Thu Aug 02, 2018 12:37 pm

troed wrote: As long as GLUE is in color then monitors will accept the signal, and the Shifter manically outputting lots of pixels will just make for some really nice dithering one bitplane possibilities.


So here's another reason for ube to make new firmware for the ubeswitch. This mode (color sync but mono output) will output video on the mono pin. So even if a regular SC1224 or 15KHz flatscreen etc should be able to display it, unless you route the mono output to the RGB pins you won't get an image.

I'm not certain it can be autodetected though. Sync signals look exactly like regular color modes. New hardware which always muxes mono and RGB should work.

(1280x200 in one bitplane will make awesome demo effects)

Regarding the missing BLANK on STE. It might be possible to get around it using synclocked code. Will be as problematic to code around as a regular fullscreen, and won't enable the mode in GEM, but for demos it should do.

(I'm on holiday with no Atari access, haven't thought about it in detail)

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby keops » Thu Aug 02, 2018 2:54 pm

Excellent!

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ijor » Fri Aug 03, 2018 1:15 pm

troed wrote:Regarding the missing BLANK on STE. It might be possible to get around it using synclocked code. Will be as problematic to code around as a regular fullscreen, and won't enable the mode in GEM, but for demos it should do.


Doesn't seem to be possible, at least according to the schematics. BLANK is asserted constantly whenever GLUE rez bit one is set on the STE. There are no BLANK comparators for mono, as they are on STF GLUE.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby ijor » Fri Aug 03, 2018 3:20 pm

Or to be more precise, to avoid BLANK being forced, it would require setting both SHIFTER and GLUE in color during the whole horizontal active display. And only set to MONO at the borders. Switching to color and back to mono right away as the typical overscan switch won't work.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby troed » Fri Aug 03, 2018 3:36 pm

Well running GLUE in color during active display should work, right? Still only two changes per scanline.

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Re: The SECRET VIDEO MODE in an ST: 400 lines in COLOR (and with 72 Hz)!

Postby PeterS » Fri Aug 03, 2018 4:25 pm

So does that mean the available video modes would become:

Low : 320 × 200 (16 colour), palette of 512 colors
Med : 640 × 200 (4 colour), palette of 512 colors
High : 640 × 400 (mono)

Secret : 320 × 400 (4 colour), palette of 512 colors


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