Bitfields for OPTi FireLink/FireBlast "HceControl" register:
Bit(s)	Description	)
 31-9	reserved
 8	A20 gate state
 7	IRQ12 active (write 1 to clear)
 6	IRQ1 active (write 1 to clear)
 5	A20 gate sequence
	1  D1h written to port 64h
	0  other than D1h written to port 64h
 4	external IRQ emulation enable
 3	IRQ enable
 2	character pending emulation enable
 1	(read-only) emulation interrupt condition
 0	emulation enable
SeeAlso: #00902,PORT 0064h