Int 4A  - Acorn Bbc Master 512 - "osword" - Misc Functions Using Control   [O]

   AL = function code
       FAh transfer data between 80186 and 65C12 I/O processor
   DS:BX -> control block (see #2882)

Return: FLAGS destroyed
   control block updated

Note:  there are more functions than are listed here, but details are not
     available

See Also: INT 40"Acorn",INT 4B"Acorn",INT 4C"Acorn"

Format of BBC Master control block for function FAh:
Offset Size    Description (Table 2882)
 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 #2883)

Bitfields for 65C12 memory access control:
Bit(s) Description (Table 2883)
 7 unused
 6 always use main screen memory if I/O addr 3000h-7FFFh (overrides bit 5)
 5 use shadow screen memory if screen address specified
 4 use current ROM rather than ROM selected by bits 3-0 (only if I/O
     address between 8000h and BFFFh)
 3-0   paged ROM number