Mail Archives: djgpp/1997/01/09/18:45:20
> This may not have been in the *original* IBM VGA card, but according
> to my old book in programming for PC video subsystems, the EGA, the
> VGA, and the MCGA supports generating a Vertical Interrupt on IRQ2
> whenever vertical retrace starts, and explains how this is done. On
> the EGA/VGA, these interrupts appears to be controlled by the CRTC
> Vertical Retrace End register (CRTC register 11h) bits 4 and 5, though
> I haven't really studied this in detail.
The original true-blue IBM VGA only had a VSYNC interrupt on the PS/2
models 25 and 30 (ISA bus). The models 50 and 60 (the ones with MCA
slots), had no vsync.
The all had the status bits for it, though.
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