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Power down the CNC system completely and wait 30 seconds for capacitor discharge.

Ensure the machine is in a safe state and all axes are stationary.

Open the NCU cabinet and visually inspect the communication module slot (typically located on the main NCU backplane). Verify that an RS422 board is physically present and fully seated.

Observe ESD precautions; ground yourself before handling boards.

If the module is missing, install the correct Siemens RS422 digitizer communication board (typically part number 6FC5372-0AA30-0AA0 or equivalent for your NCU generation) into the available slot until it clicks fully into place.

Ensure the board orientation matches the slot keying; do not force insertion.

Power the system back on and monitor the boot sequence. The alarm should clear once the module is detected during NCK initialization.

Power down the NCU and reseat the RS422 board by fully removing it, inspecting the connector pins for corrosion or damage, then reinserting it firmly until the retention clips engage.

Do not touch the gold connector contacts; handle the board by its edges only.

Access the NCU Diagnostics menu (typically via HMI: Main Menu > Diagnosis > Hardware) and check the detected modules list to confirm whether the RS422 board appears in the inventory after reboot.

If the module still does not appear, proceed to step 3.

Verify that the RS422 module firmware version is compatible with the installed NCU/SINUMERIK version (check via Siemens service documentation or the board label). If a firmware mismatch is suspected, contact Siemens service for a firmware update or module replacement.

Access the Machine Data editor via the HMI or SINUMERIK engineering software (Manage > Machine Data). Navigate to the channel-specific parameters and locate MD $MN_ASSIGN_DIGITIZE_TO_CHAN.

Do not modify parameters without proper authorization and backup.

Verify that the channel number assigned in MD $MN_ASSIGN_DIGITIZE_TO_CHAN matches the physical channel configuration on the machine. If digitizing is not required, set the parameter to 0 (disabled) or comment it out.

Disabling this parameter will prevent digitizing functionality; ensure this is intentional.

If digitizing is required, ensure the RS422 module is installed (see Cause 1), then save the machine data and perform a cold start (power cycle) to re-run the boot diagnostics.