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Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-18, 17:10

Did you set your I/O port address jumper back to 3xx? In an IBM system EGA installation, the ROM is loaded at boot, not by a TSR. The IBM motherboard is jumpered to load the ROM directly over initializing MDA/CGA from the motherboard BIOS, even if the MDA/CGA is primary. It is the responsibility of …

Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 04:40

If you know the pinout for the sequencer, and can measure CCLK and CLKIN, maybe create a short table on what it is capable of doing in each mode. I discussed my bad card here. http://www.vcfed.org/forum/showthread.php?76762-IBM-EGA-Card-Clock modem7 shared his readings in post 16. My sequencer …

Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 01:28

While I don't know how the card divides the clock by two, I am positive it's not due to a divide-by-2 feature in the standard EGA registers that would be disabled by software setting custom video modes. If they would use the standard EGA divide-by-2 feature to get from 28.5MHz to 14.25MHz, how …

Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 01:25

CLKSEL is bits D2-D3 of the 03C2 register, with four choices according to the IBM EGA Tech Ref: 00=14Mhz, 01=16Mhz, 10=EXT OSC (feature connector), and 11=unused. I think the usual configuration for "superEGA" cards is to connect the faster oscillators to CLKSEL=10 (since apparently nobody ever …

Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-10, 00:16

So that renders this card useless for what I'm intending to do: 8088MPH-style register manipulations during the active video period. Which relies on having the 8254 PIT timer and the EGA CRTC both running from the same clock. (Obviously only in the 200 line modes.) Even though EGA offers a vertical …

Re: Sigma Designs EGA cards - a deep dive

Posted on 2020-10-09, 21:53

But I want an EGA card that works in my Turbo XT at 10Mhz! So let's try the ERGO480.... it has two oscillators onboard, a 28.500Mhz and a 32.000Mhz; hmm, very close to 2x of the standard 14.318Mhz OSC signal and the 16.257Mhz oscillator that one expects an EGA card to use. No matter what I do, …

Re: What specs to look for to play DOS Quake, Diablo II, Warcraft III, etc. at HIGH native resolutions?

Posted on 2020-01-11, 21:21

My treshold for "smooth" must be really low - in simulated LAN game (4 computers, me as observer, medium map) it still looks OK, even with some bigger fights taking place over the map :) Version is 1.00 - I guess in its current state, after many patches, the game is way more taxing then it once was …

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