This command indicates the end of the main program. It is the same as
the END command when the PLC executes this command.
The CALL command program must be written after the FEND command,
and the SRET command is added to the end of the subprogram.
When using the FEND command, an END command is also needed.
However, the END command must be placed at the end, after the main
program and subprogram.