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Re: Diy VL bus

Is it one pin that all devices talk to or is there a pin for each device? Each VL device has a totem pole output for LDEV (sometimes called differently, it's called LOCA on the S3 graphics chips for example). Most chipsets just have one input (again, names vary. UMC calls it ELBA instead of LDEV). …

Re: Diy VL bus

My other YT comment under Atheatos video: You replied to a comment on a video at 2021-06-03 17:20:40 UTC. ... LCLK is the FSBx2. LCLK is FSB x1 on the 486 local bus, and it also is that way in VL in 486 mode. Possibly you are right about VLB in 386 mode, but this is extremely rare. Most VL 386/486 …

Re: Diy VL bus

Afaik VLB itself is just a small arbitration circuit added to 486 bus. The "small arbitration circuit" is the key to implementing local bus add-on cards (like VL, or earlier local busses). A local bus cards "takes over" the frontside bus if it is addressed and stops the chipset from processing the …

Re: IBM VGA BIOS initialization

Great info, and all that makes sense. I am a little puzzled as to why the Maximum Scan Line is set differently in the CGA 320x200 mode (1) vs EGA 320x200 mode (0). Or what the purpose of the '2T4' bit is if it's set for those modes but not mode 13h. I don't understand what you mean by "2T4". Maybe …

Re: IBM VGA BIOS initialization

I got things more or less working, I think. One surprising thing in Mode 13h, is that the CRTC is set up for 80 characters and 400 lines instead of the expected 320x200. I don't see any of the bits that would affect the clock enabled. How does the VGA know to double the resolution? First the most …

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