I notice that the VGA has multiple graphics/text mode bits? Both the graphics and the attribute registers have one.
Misc graphics register bit 0.
Attribute Mode control register bit 0.
Why is this? What happens when those bits aren't the same?
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wrote:Why is this?
It's a holdover from EGA, where the CRTC, sequencer, graphics controller and attribute controller were all in different chips, and hence control bits were duplicated in every chip that needed them.
What happens when those bits aren't the same?
Probably implementation specific, ie will vary between different chipsets.
Is it known how it was in the VGA?
When does the Misc graphics register take effect?
Where does the Attribute mode control take effect?
I'm currently using the attribute mode control in attribute calculations (blink bit position at bit 3 or 7 depending on graphics or text mode) and the misc graphics register in all other locations (shift modes vs text mode). Is this correct?
Author of the UniPCemu emulator.
UniPCemu Git repository
UniPCemu for Android, Windows, PSP, Vita and Switch on itch.io
