OSWORD &06 (6) - Write I/O processor memory (Acorn MOS 1.00 and later)
On entry: XY!0=address to write to XY?4=byte to be written.
Some systems recognise screen memory at &FFFExxxx and sideways ROMs at &FFrr8000-&FFrrBFFF.
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,
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
All 8-bit Acorn systems write to whichever ROM/RAM is paged in. All except the BBC B+ write to main memory. The B+ recognises &FFFExxxx to write to the shadow screen memory, otherwise it writes to main memory. It is possible to write a modified Tube Host that intercepts OSWORD 5 and 6 to access extended memory, but most programs rely on adding an extra OSWORD call.
- OSWORD &05
- OSWORD &FA
- OSWORD &FF
- MemIO library at http://mdfs.net/blib