Programming instructions

CALL – Call Subroutine

SRET – Subroutine Return

FEND – Main Routine Program End

The call subroutine command allows the execution of a section of code only

when activated. Unlike the jump command, execution of the main program

resumes from the point where the subroutine was called. By removing code from

the main ladder, scan times can be improved, since the subroutine code is only

processed when the subroutine is active.

Subroutines are coded at the end of a PLC program. Main program execution is

stopped at the FEND instruction, and the subroutines are created between this

instruction and the END instruction. Subroutines are referenced by their pointer

number for a starting point, and the next SRET command is considered the end

of that subroutine. When the logic in front of it is active, the CALL instruction

executes the code for that subroutine until the SRET subroutine return command

is reached. Once the SRET is reached, program execution returns to the main

ladder program and continues from the location of the CJ instruction.