Format of BBC Master control block for function FAh:
Offset	Size	Description	)
 00h	BYTE	number of parameters sent to I/O processor (0Dh,0Eh)
 01h	BYTE	number of parameters read from I/O processor (01h)
 02h	DWORD	I/O processor address
 06h	DWORD	80186 segment:offset address
 0Ah	WORD	number of bytes to transfer
 0Ch	BYTE	operation type
		00h write to 65C12 at 24 us/byte
		01h read from 65C12 at 24 us/byte
		02h write to 65C12 at 26 us/word
		03h read from 65C12 at 26 us/word
		04h write to 65C12 at 10 us/byte using 256-byte blocks
		05h read from 65C12 at 10 us/byte using 256-byte blocks
 0Dh	BYTE	65C12 memory access control (only used if offset 00h = 0Eh)
		(see #03212)