Bitfields for retrieval mode:
Bit(s)	Description	)
 0	enable data retrieval
 1	0 = interrupt-driven
	1 = polling mode
 2	0 = read port 60h everytime
	1 = read port 60h only when OBF of port 64h is set
 3	0 = don't call old INT 9
	1 = call INT 9 before our INT-handler
 4-7	reserved
SeeAlso: #02708,#02710