Int 15H [PS/2] Function C4H (196) Programmable option select

Returns the base Programmable Option Select register address, enables a slot for setup, or enables an adapter.

Call with:

AH = C4H

AL = subfunction

00H to return base POS adapter register address

01H to enable slot

02H to enable adapter

BL = slot number (if AL = 01H)

Returns:

If function successful

Carry flag = clear

and, if called with AL = 00H

DX = base POS adapter register address

If function unsuccessful

Carry flag = set

Notes:

This function is available only on machines using the Micro Channel Architecture (MCA) bus.

After a slot is enabled with Subfunction 01H, specific information can be obtained for the adapter in that slot by performing port input operations:

Port Function 100H MCA ID (low byte) 101H MCA ID (high byte) 102H Option Select Byte 1 bit 0 = 1 if enabled, = 0 if disabled 103H Option Select Byte 2 104H Option Select Byte 3 105H Option Select Byte 4 bits 6—7 = channel check indicators 106H Subaddress Extension (low byte) 107H Subaddress Extension (high byte)