OSWORD &05

OSWORD &05 (5) - Read I/O processor memory Acorn MOS 1.00 and later

On entry:
 XY!0=address to read from
On exit:
 XY?4=the byte read

Some systems recognise screen memory at &FFFExxxx and sideways ROMs at &FFrr8000-&FFrrBFFF.

Coding

The following routines can be used to copy data to and from I/O memory regardless of the location of the calling program. It requires X%=>5-byte control block, Y%=X%DIV256.

    DEFPROCmem_rd(io%,mem%,num%)
    A%=5:REPEAT
      !X%=io%:CALL&FFF1:?mem%=X%?4
      io%=io%+1:mem%=mem%+1:num%=num%-1
    UNTILnum%<1:ENDPROC
    :
    DEFPROCmem_wr(io%,mem%,num%)
    A%=6:REPEAT
      !X%=io%:X%?4=?mem%:CALL&FFF1
      io%=io%+1:mem%=mem%+1:num%=num%-1
    UNTILnum%<1:ENDPROC

    REM To read a single byte:
    !X%=addr:A%=5:CALL&FFF1:byte=X%?4
    :
    REM To write a single byte
    X%?4=byte:!X%=addr:A%=6:CALL&FFF1

Implementations

All 8-bit Acorn systems read from whichever ROM is paged in. All except the BBC B+ read from main memory. The B+ recognises &FFFExxxx to read from the shadow screen memory, otherwise it reads from main memory.

See Also

• OSWORD &06
• http://mdfs.net/Docs/Comp/BBC/Oswords
• MemIO library at http://mdfs.net/blib

Jgharston 23:56, 30 October 2011 (UTC) Jgharston (talk) 04:27, 29 March 2015 (UTC)