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;* DisableCga - Disables CGA video by reprogramming the control register.
;*
;* Shows:   Instructions - cli     sti
;*
;* Params:  None
;*
;* Return:  None
 
DisableCga PROC USES ax cx dx           ; Preserve registers
 
        mov     cx, -1                  ; Set maximum loop count
        mov     dx, 03DAh               ; Address of status register
 
        .REPEAT
        in      al, dx                  ; Get video status
        .UNTILCXZ !(al & 8)             ; Until retrace end/timeout
        cli                             ; Disallow interruptions
        mov     cx, -1                  ; Reset loop count
 
        .REPEAT
        in      al, dx                  ; Get video status
        .UNTILCXZ al & 8                ; Until retrace start/timeout
 
        sub     dx, 2                   ; DX = address of control reg
        mov     al, 1                   ; Value to disable CGA video
        out     dx, al                  ; Disable video
        sti                             ; Reenable interrupts
        ret
 
DisableCga ENDP
                                    -♦-