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Siemens SINUMERIK Controller
Servo/Axis · Intermediate · 30-120 minutes
Siemens 840D 6500 - NC memory full
Alarm 6500 fires when the NCK file system buffer memory is exhausted, preventing allocation of new memory blocks for NC programs, drive data, MMC configuration files, or FIFO buffers. This typically occurs during system initialization or when accumulated file data exceeds the available RAM allocated to the NC kernel (controlled by MD 18100 'NCK_MEMORY_SIZE').
6500
Siemens 840D 6500 - NC memory full
NC memory full
Siemens SINUMERIK alarm 6500: NC memory full. This alarm indicates a fault or error condition on the SINUMERIK 840D control. Refer to the Siemens SINUMERIK alarm documentation for the complete description and remedy.
Root Cause Summary
Alarm 6500 fires when the NCK file system buffer memory is exhausted, preventing allocation of new memory blocks for NC programs, drive data, MMC configuration files, or FIFO buffers. This typically occurs during system initialization or when accumulated file data exceeds the available RAM allocated to the NC kernel (controlled by MD 18100 'NCK_MEMORY_SIZE').
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Access Diagnostics → File System via HMI/HHU. Check NCK file system status and available free space. Compare against MD 18100 'NCK_MEMORY_SIZE' parameter (typical range 8000-16000 KB).
Do not reset parameters yet; document current state first.
- 2
Delete unnecessary .mpf, .spf, .opt, and backup .bak files from /NC/PROG directory via HMI File Manager. Target files >10 MB or duplicate program versions. Verify deletion via SINUMERIK directory listing.
Ensure deleted programs are backed up externally before removal.
- 3
Execute file system defragmentation: Navigate to Diagnostics → File System Maintenance → Defragment NCK FS (if available on your 840D version) or power-cycle the controller after clearing space to trigger file system rebuild.
- 4
Verify alarm clears on next NC startup. If persistent, increase MD 18100 value by 2000 KB increments (via offline parameter editor) and reload parameter set via /NC/PARAM/ACTIVE directory.
Changing MD 18100 requires PLC recompile and full memory allocation recalculation; coordinate with system integrator.
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