CALLS, SBRT, RET
CALLS label
SBRT label
The CALLS command calls a subroutine with the specified label.
SBRT marks the subroutine's starting point and RET marks the subroutine'
end.
Please be aware that when adding sub-routines to your program, RET must be appended to the end of main program, before the first subroutine. END must be placed at the very end of the main program after the last subroutine.