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EGA deep dive

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First post, by rasteri

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I decided to take a deep dive into the EGA capabilities of my Amstrad PC1640.

Had lots of fun along the way - built a circuit to convert CGA/EGA to analog for the GBS-8200, using an EEPROM for the encoding logic (got the idea from the IBM5154 service manual).

Also got EGA hi-res mode working on the GBS-8200 using gbs-control.

Also did some investigating of the weird 64-color mode used on Rambo 3 and Ironman Super Offroad.

Also found time to stick a VGA card in there and play with dual monitor support.

Full video is here -

https://www.youtube.com/watch?v=vwKA1z8tg1g

Reply 1 of 8, by root42

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Oh, I still have a GBS 8200. Such a circuit would be handy! Will check out the video later. Thanks!

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80486DX@33 MHz, 16 MiB RAM, Tseng ET4000 1 MiB, SnarkBarker & GUSar Lite, PC MIDI Card+X2+SC55+MT32, OSSC

Reply 3 of 8, by root42

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maxtherabbit wrote on 2020-04-15, 21:03:

GBS-Control is godtier. NEVER use a stock GBS though it is total shit

Please elaborate! I haven’t used the GBS yet. Since it couldn’t sync with my VGA properly I bought a OSSC straight away.

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80486DX@33 MHz, 16 MiB RAM, Tseng ET4000 1 MiB, SnarkBarker & GUSar Lite, PC MIDI Card+X2+SC55+MT32, OSSC

Reply 5 of 8, by Anonymous Coward

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Paradise EGA can do 64 colours in lowres on a 5154? That deserves more investigation.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 6 of 8, by rasteri

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Anonymous Coward wrote on 2020-04-16, 14:55:

Paradise EGA can do 64 colours in lowres on a 5154? That deserves more investigation.

It certainly does appear so.

I don't have a 5154 to test it on, but I just built an MCE2VGA. It does 64-color mode selection based on VSYNC polarity just like the 5154 does, and doesn't (AFAIK) have a manual override.

Rambo 3 in Paradise 64-color lowres mode displays the correct colors on the MCE2VGA, so it should do the same on any other autoswitching EGA monitor, including the 5154.

As expected, Ironman Super Offroad in 64-color lowres mode doesn't display correctly on the MCE2VGA at all, since it outputs normal VSYNC polarity. Inverting the sync using a 74LS04 makes it display correctly (though the geometry is all screwed up, I suppose the MCE2VGA must use the sync polarity for other stuff than just color mode detection).

Anyone know of any hardware docs for Paradise EGA cards that might mention this weird mode? Presumably they distributed programming guides to software vendors at least?

Reply 7 of 8, by Anonymous Coward

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What about the Boca cards? Do they work the same as the Paradise? I don't have Paradise EGA, but I do have Boca.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 8 of 8, by rasteri

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Anonymous Coward wrote on 2020-04-23, 00:08:

What about the Boca cards? Do they work the same as the Paradise? I don't have Paradise EGA, but I do have Boca.

I'm not sure, but if I run Rambo 3 in Boca mode on my Paradise I get exactly the same result (low-res, inverted vsync, 17.8KHz hsync). So the Boca and Paradise cards must have very similar register sets at least.

I can't find any more information on programming the Boca than I can the Paradise. Probably some disassembly of Rambo 3 is in order.

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