The *FX command can be used to control some of the system's "special effects", such as keyboard repeat rates or manipulating the Escape condition.
*FX is in fact a convenient way to call OSBYTE routines from BASIC programs or the command line. For example, to set the keyboard's auto-repeat rate you set the routine number A to 12 and load the repeat rate into L, then call OSBYTE like this:
A%=12 L%=4 CALL &FFF4
*FX takes up to three arguments, A, L and H, and passes them to OSBYTE. The above code could therefore be rewritten as follows:
All arguments are specified in decimal. The L and H arguments are optional.
For a full list of available *FX routines see the OSBYTE section.