268

Review the part program for nested M98 subroutine calls and count the maximum nesting depth (subroutines calling other subroutines).

Verify each M98 call has a corresponding M99 return statement in the called subroutine program.

Reduce nesting levels by restructuring the program logic - combine subroutines or eliminate unnecessary nesting layers to stay within 4 levels maximum.

Check parameter 3107 (if available on your control) which defines the subroutine nesting level limit and verify your program stays within this value.

Search all subprograms (O-number programs) for M99 commands and verify each subprogram ends with M99 before the program end marker.

Do not place M99 in the main program (except for loop-to-start applications) as this can cause stack issues.

Check for conditional statements (IF/GOTO) that might skip over M99 commands, preventing proper subroutine returns.

Verify M99 commands do not include a P address pointing back to earlier program locations within subroutines, which can create infinite loops.

Test the corrected program in single block mode to confirm proper entry and exit from each subroutine level.

Press RESET button on the control panel to completely clear the retrace stack and all program execution states.

Avoid using program restart or search functions in the middle of nested subroutine execution - always restart from the program beginning (O-number start).

If background editing is enabled, disable it temporarily (parameter 3107.7 or similar) and test if the alarm clears during program execution.

Changing parameters requires proper authorization and may require a control restart.

Run the program from the beginning without any search or restart operations to verify normal execution without stack overflow.