6520

Access the NCK machine data editor via HMI or SINUMERIK Operate: navigate to Maintenance > Machine Data > General > Protocol Management and locate $MN_MM_PROTOC_NUM_FILES (typically a DWORD parameter in the 600xx range).

Do not edit while NC programs are executing or during automatic operation.

Document the current value of $MN_MM_PROTOC_NUM_FILES and count the number of active protocol users in the system configuration (check PLC program diagnostic data, HMI protocol settings, and NC kernel trace modules).

Increase $MN_MM_PROTOC_NUM_FILES to a value greater than the number of protocol users identified (recommended: add 2-3 buffer slots above the actual count to allow for future expansion).

Increasing this value consumes additional NCK memory; do not set excessively high values (typical range: 4-16).

Save the machine data change and restart the NCK (Ctrl+Restart via HMI or power cycle the system). Verify alarm 6520 no longer appears during system boot and protocol initialization.

A warm restart (software restart) may not reload all machine data; perform a cold restart if the alarm persists.

Review the system event log and NCK diagnostic buffer (via Siemens SINUMERIK Diagnostics or HMI menu: Service > Diagnostics > NCK Messages) to identify which protocol user module triggered the alarm and at what point in the boot sequence.

Check the PLC program source code (in TIA Portal or offline project) for any conditional or timer-based protocol module initialization; verify that module activation logic does not exceed the $MN_MM_PROTOC_NUM_FILES limit.

Disable non-essential protocol users temporarily (via PLC code or HMI configuration) and re-test system startup; if alarm 6520 clears, the culprit protocol module is confirmed.

Increase $MN_MM_PROTOC_NUM_FILES by the number of protocol users you intend to enable, then re-enable the modules and restart the NCK to confirm operation.

Verify the NCK firmware version matches the expected version for your 840D/840D sl system (check via HMI: Machine > System Info or SINUMERIK Operate > Service > System Information). If a firmware mismatch is detected, refer to Siemens firmware update documentation.

Perform a full NCK restart (power cycle or warm restart) and monitor the startup sequence for any additional alarms that may indicate memory corruption or hardware issues.

If alarm 6520 persists after restart, use the Siemens Service and Support tool to perform an NCK memory diagnostic scan (typically available in Maintenance > Diagnostics > Memory Test or similar path depending on HMI version).

Memory diagnostic scans may take 5-10 minutes and require the system to be in idle state.

If memory diagnostics reveal errors, contact Siemens field service to schedule NCK firmware re-flash or hardware replacement. As a temporary workaround, reduce the number of active protocol users until hardware service is available.