PS051

Review the active part program structure and trace all M98 subprogram calls. Count the maximum nesting depth from main program through each subprogram level (Main > O1000 > O2000 > O3000 = 3 levels).

Check parameter 3107 (Subprogram Nesting Level) in SYSTEM > PARAM > search [#3107]. Note the maximum allowable nesting value. On 0i/16i series this is typically fixed at 4 levels; on 30i/31i/32i it may be adjustable.

Restructure the part program to reduce nesting depth by consolidating subprograms, eliminating unnecessary intermediate subprogram calls, or using macro variables (G65) with local subprograms instead of deeply nested M98 calls.

Test the modified program in single block mode (SINGLE BLOCK key ON) while monitoring the program stack in CURRENT screen > PROGRAM > STATUS to verify nesting depth remains within limits.

In EDIT mode, search all subprograms in memory using ADDRESS key [O] to list all program numbers. Document each M98 call and the target subprogram number to create a call tree diagram.

Identify circular calling patterns where any subprogram in the call chain eventually calls a parent subprogram already on the stack. Check for conditional M98 calls (IF/WHILE statements) that may not have proper exit conditions.

Correct the program logic by removing recursive calls, adding proper loop counters using macro variables (#100-#199 for local, #500-#531 for common), or implementing external loop control in the main program instead of within subprograms.

Verify program flow using PROGRAM > CHECK or DRY RUN mode with Feed Hold ready. Monitor CURRENT > PROGRAM screen to observe subprogram call sequence and ensure no repetitive nesting occurs.

Recursive calls can fill the program stack in milliseconds. Always test corrected programs in dry run with machine locked out.

Verify each subprogram called by M98 contains a proper M99 return statement before the program end. In EDIT mode, open each subprogram and scroll to the end to confirm M99 is present and not commented out.

Check program integrity by comparing CRC or file size if programs were loaded via DNC, USB, or memory card. Re-transfer suspect programs using EDIT > I/O channel F-EDIT or SYSTEM > FILE menu to ensure clean data.

Examine parameter 3404 bit 0 (M99 in main program) in SYSTEM > PARAM to verify proper M99 behavior settings. Check diagnostics 0300-0303 (Program Path Status) to identify if program pointer is advancing correctly through nested calls.

If corruption is confirmed, delete the affected subprograms using EDIT > DELETE > [O####], then reload verified clean copies. Execute a control reboot (SYSTEM > power cycle) to clear any residual stack data before retesting.

Always backup all programs to external media via SYSTEM > FILE > DEVICE before deleting potentially corrupted data.