Bitfields for Intel 82425EX/82371 X-bus Chip Select A register:
Bit(s)	Description	)
 7	extended BIOS enabled at FFF80000h-FFFDFFFFh
 6	lower (E000h) BIOS enabled
 5	trigger IRQ13 on FERR#
 4	IRQ12 mouse function enabled
 3	(82371AB only) alias accesses to PORTs 63h/65h/67h to 61h
	(else) reserved (0)
 2	BIOS memory write protect
 1	keyboard controller addresses (60h,62h,64h,66h) enabled
 0	RTC addresses (70h-77h) enabled
SeeAlso: #01083,#01167,#01088,#01102