PS077

Review the active program structure and count nesting levels. Navigate to EDIT mode and trace all M98 Pxxxx calls through each subprogram level to identify maximum depth reached.

Check parameter 3107 (subprogram nesting level limit). Navigate SYSTEM > PARAM > search P3107. Typical values: 4 for 0i/16i/18i series, 10 for 30i/31i/32i series. Verify current program does not exceed this limit.

Restructure the part program to reduce nesting depth. Replace deeply nested M98 calls with sequential subprogram calls at higher levels, or consolidate repetitive operations into fewer subprogram levels.

If nesting is legitimately required and control supports higher limits, consult Fanuc documentation for your series to determine if parameter 3107 can be safely increased within hardware memory constraints.

Increasing nesting depth beyond factory defaults may cause memory issues or system instability on older control models with limited RAM

Examine all subprograms in memory for recursive calls. Check if any Oxxxx program contains M98 Pxxxx where xxxx matches its own program number or calls another subprogram that eventually calls back to the original.

Use EDIT > PROGRAM > LIST to display all programs in memory. Document the call tree structure: which programs call which subprograms, and identify any circular references.

Correct the recursive logic by redesigning program flow. Use conditional branching (IF/GOTO statements with macro variables) or looping structures (WHILE/DO) instead of recursive M98 calls for repetitive operations.

Verify program logic after correction by dry-run execution in EDIT mode with single block enabled, monitoring CURRENT > PROGRAM display to confirm subprogram call sequence does not repeat indefinitely.

Verify every subprogram called with M98 contains a corresponding M99 return statement. Navigate EDIT mode and inspect each Oxxxx subprogram for proper termination. Missing M99 causes unpredictable nesting behavior.

Check for program memory corruption. Navigate SYSTEM > DIAGNOSIS > PMC and check diagnostic screen #0200 (program memory status). If errors are present, backup and re-transfer programs via RS-232 or CF card.

Ensure battery backup (diagnostic #0196 bit 7) is functional before clearing program memory to prevent total program loss

Verify all M98 P-addresses reference valid existing program numbers. Calling non-existent programs may cause nesting counter errors. Cross-reference all M98 Pxxxx calls against actual program directory.

If issue persists after program verification, perform control reboot (power cycle) to clear nesting stack counters. If alarm recurs immediately, suspect SRAM or FROM/FLASH memory hardware fault requiring Fanuc field service.