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Access Siemens SINUMERIK 840D HMI and navigate to Commissioning → Machine Data → PROFIsafe Safety Configuration (typically MD 18xxx-19xxx range for safety I/O modules).

Identify the specific MD parameter referenced in alarm message %1[%2] and note the displayed maximum sub-slot address %3.

Cross-reference the hardware module documentation (e.g., PN 6SL3 or 6FC safety interface card) to confirm maximum supported sub-slot addresses for the installed module.

Verify module part number on the PCB matches commissioning documentation.

Correct the MD parameter value to remain within 0 to the maximum sub-slot address displayed in the alarm message, then perform a cold restart (POWER OFF 10 seconds, then ON) to reload NCK parameter validation.

Power down the CNC control and physically inspect the PROFIBUS/PROFINET safety I/O module installed in the control cabinet. Note the exact module part number (e.g., 6SL3 055-0 AA63-0AB0).

Compare the physical module part number against the module type recorded in the NCK configuration (Diagnostics → Module Overview or via SIEMENS STEP 7/TIA Portal if accessible).

If modules do not match, either replace the installed module with the correct high-capacity version, or update all affected PROFIsafe MDs to match the actual module's sub-slot address limits.

Always consult the machine builder's safety documentation before modifying safety I/O configurations.

After hardware correction or MD adjustment, perform a complete NCK parameter reload (Commissioning → Reset All MD to Factory → Restart) if configuration is fundamentally altered.

Access the PROFIsafe MD parameter listed in alarm %1 and verify the exact numeric value displayed (use Commissioning → Detailed View to see raw MD values without interpretation).

If the value appears corrupted (e.g., negative number, extremely large integer, or non-numeric character), delete the parameter entry and re-enter a valid sub-slot address (typically 0-3 or 0-15 depending on module).

Do not attempt to edit MD binary or EEPROM directly; use HMI only.

If the MD was loaded from an external file (.asc, .mpf, or configuration backup), reload the file from a known-good backup and re-import, ensuring the source file was not corrupted during transfer or previous edit.

Perform a control restart and verify the alarm no longer occurs. If it persists, contact Siemens Support with the MD file and a memory dump (Diagnostics → Dump) for detailed analysis.