INT 10 - VIDEO - SELECT DISPLAY PAGE
        AH = 5
        AL =
            0-7: new page value for modes 0 & 1
            0-3: new page value for modes 2 & 3
            80h: read CRT/CPU page registers [PCjr only]
            81h: set CPU page register to value in BL [PCjr only]
            82h: set CRT page register t
o value in BH [PCjr only]
            83h: set both display registers [PCjr only]
            {Corona/Cordata BIOS v4.10+}
            0: set address of graphics bitmap buffer (video modes 60h,61h)
               BX = segment of buffer
            0Fh: get address of graphics bitmap buffer (video modes 60h,61h)
Return: BH = CRT page register (if AL >= 80h)
        BL = CPU page register (if AL >= 80h)
        DX = segment of graphics bitmap buffer (video modes 60h,61h; AL=0Fh)
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