When calling the OSWRCH routine from machine code you will need to use the absolute address &40EE. However, when CALLing this routine from BBC BASIC it is recommended that you use the BBC Micro-compatible address &FFEE.
This OS call routine outputs the value in the accumulator to the current output stream. It is identical in behaviour to the BASIC VDU statement and so can be used for other purposes as well as outputting text (such as plotting shapes).
All registers are preserved.