Int 15 Fn C4 - System - Programmable Option Select (ps50+) [B] AH = C4h AL = subfunction 00h return base POS register address 01h enable selected slot for setup BL = slot number (1 to 8) 02h disable setup for all slots Return: CF set on error DX = base POS register address (if subfunction 00h) See Also: AH=C6h