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Alley Cat on Hercules Video Adapter (CGA Emulator)

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First post, by 133MHz

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Hello everyone!

Back in the day I had a 386 with a Hercules video card and an amber monitor on which I used to play some DOS games thanks to a CGA emulation TSR. I remember Alley Cat (one of my favorite PC games) not working correctly, the clotheslines never moved and the windows never opened making the game really boring. I never found out why it didn't work but I assumed it had to do with the diferences between CGA and Hercules video.

Recently I got a monochrome green display for my XT clone so I've been playing and tinkering like in the old days. I looked around for the Alley Cat problem and I found this thread. It seems that ripsaw8080 hit the nail right on the head!

Could someone post the relevant bytes I need to modify in the Alley Cat executable to get the vsync routines working on CGA-emulatng Hercules? I'm more of a hardware/electronics guy myself so x86 assembly is a bit out of my league, and I'd love to see Alley Cat finally working on a high persistence monochrome monitor!

Cheers!

http://133FSB.wordpress.com

Reply 1 of 7, by ripsaw8080

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Output of FC.EXE listing offset, original byte, and modified byte:

Comparing files ALLEYCAT.EXE and HERC_CAT.EXE
000078DE: 75 74
00007D54: 74 75
00007FBE: 75 74
00007FC3: 74 75
00008809: DA BA
0000880D: 08 80
00008D75: 75 74
000092AE: 74 75
00009656: 74 75
0000A97A: 74 75
0000AE54: 74 75
0000BD35: 74 75
0000BED5: 74 75
0000D24F: 74 75
0000D48B: 74 75

Alley Cat was originally a booter, but this is based on the DOS conversion. It works in DOSBox, so maybe will work on real hardware, but speed might be different than CGA because of different timing.

Reply 2 of 7, by 133MHz

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Damn, almost a week after I asked but I finally got some time to try this out on my XT clone... it works perfectly! The timing might be a bit different because of the 50~60 Hz difference between Hercules and CGA but between the somewhat laggy CGA emulation and the high persistence screen phosphor I can't really tell. I might shoot a video of it later. 😉

Thank you very much ripsaw8080! 😁

http://133FSB.wordpress.com

Reply 4 of 7, by Great Hierophant

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dr.zeissler wrote:
HERC_CAT.EXE ? […]
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HERC_CAT.EXE ?

Is there a patched Hercules Version of the Game?
Can't find any DL ?

Thx
Doc

You patch it yourself using a hex editor.

Of course, I doubt there was any real way to do this with a booter back in the day unless you had the skillz to crack the game and modify it to workaround the CGA vsync issue. I suppose there could be a monochrome card that emulates CGA on a monochrome TTL monitor in hardware at 60Hz, but I know it not.

This is not to say you could not run Alley Cat in monochrome. You certainly can with a composite monochrome/B&W TV, as shown in this video of the IBM PC Portable, which uses an amber screen fed with a composite connector : https://www.youtube.com/watch?v=rr4FvRoIc2g Note the "jailbars" from the less than ideal video signal.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 6 of 7, by Great Hierophant

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dr.zeissler wrote:

My EuroPC has no composit output 😀

I guess you will have to play it on your Tandy and suffer the colors. 😀

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

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