If you need a specific subroutine to run at program initialization, you can specify *INZSR in factor 1 of the BEGSR op code. On subsequent calls, the subroutine will not be executed unless LR is set on and the program is reloaded. *INZSR can contain any logic that is valid for any other subroutine; the program can also explicitly execute it by using either the EXSR or CASxx op code.