These two OSBYTEs are part of a set that read/write OS memory locations. In each case they set the contents to (<OLD VALUE> AND Y) EOR X, then return the old contents in X and the content of the next location in Y (to help with reading 16-bit values). If you only want to read the old value, as recommended for these two, you make the call with X=&00 and Y=&FF.The https://beebwiki.mdfs.net/OSBYTE_%26EA and https://mdfs.net/Docs/Comp/BBC/OsbyteA6 are rather cryptic.
Statistics: Posted by Coeus — Tue Sep 24, 2024 10:19 pm