Register parameters

IN:
     A = character to be written
OUT:
     Fc = 0 always (error handler is never provoked)

Registers changed after return:
     A.BCDEHL/IXIY same
     .F....../.... different

Notes

OS_Out may also be used to write screen driver codes by writing them in a series of OS_Out sequences, eg. 1, '2', '+', 'B' to switch on bold typeface.