Int 1A Fn B188  - Pci Bios V2.0c+ - Read Configuration Byte (32-bit)       [X]

   AX = B188h
   BH = bus number
   BL = device/function number (bits 7-3 device, bits 2-0 function)
   DI = register number (0000h-00FFh)

Return: as for AX=B108h

Note:  the meanings of BL and BH on return were exchanged between the initial
     drafts of the specification and final implementation

See Also: AX=B108h,AX=B189h,AX=B18Ah