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s it ok when EGA display dont properly work with CGA cards ?

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Sandisk78

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Apr 2, 2016
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s it ok when EGA display dont properly work with CGA cards ? Tried two cards - one from IBM 5160, the other from Bulgarian XT clone Pravetz16. With EGA cards display works ok.

Digi_new_229.jpgDigi_new_230.jpg
 
They are different scan frequencies, so that is what I would expect. You would need a multisync monitor to do both with one monitor.
 
thanks for tha info. Once I had a Cortran display that worked both in CGA and EGA. Now I get it that later and cheap EGA displays dont work in both modes...
 
Sandisk78 said:
thanks for tha info. Once I had a Cortran display that worked both in CGA and EGA. Now I get it that later and cheap EGA displays dont work in both modes...
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That doesn't seem right. EGA cards output modes that are fully backwards compatible with CGA, IE, the 320/640x200 line modes. Unlike VGA, which double-scans these modes, they are *literally* the same from an electrical standpoint as the signals from CGA card. As this page explains, the way an EGA monitor decides what mode to display in, 200 or 350 lines, is determined by the polarity of the vertical sync pulses. An EGA monitor that couldn't display both modes would be sort of useless outside of, I don't know, an industrial/business context?, because it wouldn't be able to display a lot of software. (Like almost all EGA games.)

Looking at your screenshots what you're seeing on the screen there doesn't look like a sync problem. There are perfectly formed characters mixed in with the color blocks, which are also perfectly square and in sync. I don't know why you're getting that garbage display with those monitors attached, but I don't think sync is the answer.
 
krebizfan said:
The old discussion points to a lot of EGA only monitors that won't handle CGA signals.
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I don't see a "lot", I see one mention from one person who said they had one. Everyone else in that thread said it should work, and even the OP found his worked when he actually tried it.

Again, if you look at the screenshots the monitor seems to be synch-ing perfectly fine, they're just syncing with a garbage display. What is the make and model of those monitors, and is it a stock, genuine CGA card in the 5160? I'm wondering if one of the members of this pair is doing something proprietary on the connector that's somehow shorting out the PC enough to make it hang on a garbage screen.

(I recently ran into an issue with my Tandy 1000 EX in that a pin that's normally NC on a CGA card is actually connected to "green" on the Tandy's connector because apparently the Tandy has some secret support for a monochrome mode using that pin for video, and because of that connection green was getting shorted to ground if I connected it to my Commodore 1084 monitor with a cable with all pins present. Maybe something similar but worse is happening here?)
 
EGA monitors do work with CGA cards. The pictured one works decently, the vertical size can be extended via monitor controls. The problem is related to your computer and/or its videocard.
 
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Just as a sanity check; I realized you said you tried two CGA *cards* from two different computers, are you sure you configured the computer you placed them in correctly? On an old machine with DIP switches you have to adjust them differently depending on if you have a CGA, Mono, or EGA/VGA card installed.
 
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