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Access SINUMERIK HMI or Automation Tool and navigate to Diagnostics > Alarms. Note the exact timestamp and any secondary alarm codes in the alarm buffer that may indicate PLC-side failures.

Check MD $MN_PLC_RUNNINGUP_TIMEOUT value in NCK parameter list (access via HMI: Machine Data > System > PLC Interface or via SIMATIC Automation Tool). If value is too restrictive (< 15 seconds for systems with many I/O modules), increase incrementally (e.g., from 15000ms to 25000ms) and cold restart the control.

Changes to MD parameters require control power cycle to take effect. Ensure machine is in safe state before restart.

Verify PLC program executes OB100 (startup block) successfully without runtime errors. Check PLC diagnostic buffer in TIA Portal or STEP7 for compilation errors, missing function blocks, or watchdog timeouts that delay DP initialization.

If alarm persists, perform a cold restart (power cycle) of the entire system, ensuring the PLC CP (Communication Processor) fully initializes before the NCK begins requesting DP configuration.

In SIMATIC Automation Tool (or TIA Portal), open Hardware Configuration and verify that the DP interface (typically PROFINET or PROFIBUS module) is assigned to the correct CPU slot and that the interface parameters match the physical hardware installed on the control cabinet.

Check NCK parameter MD $MN_PLC_LINK_TYPE and MD $MN_PLC_LINK_ADDRESS to confirm they correctly define the communication interface (typically PROFINET with specific IP address or PROFIBUS address). Verify these match the PLC configuration in Automation Tool.

Run Network Diagnostics: In HMI, navigate to Service > Diagnostics > Network and check for DP link errors, packet loss, or interface down status. Also verify PROFINET/PROFIBUS cable connections and ensure all switches/connectors are secure and not damaged.

If using PROFINET, check for IP conflicts and confirm gateway/subnet settings match between NCK and PLC. Perform a system rebuild in Automation Tool (compile PLC code and download to hardware) to ensure configuration consistency.

Open PLC source code in TIA Portal and review OB100 (Startup Block) and any system startup modules. Verify that DP configuration function blocks (e.g., PROFINET Configurator or equivalent) are present and called with correct parameters before the PLC signals ready to NCK.

Check that the DP slave configuration descriptor is populated with all required I/O modules, slave addresses, and safety integrity level (SIL) parameters if using PROFIsafe. Ensure no configuration steps are skipped or conditional (gated by flags that may not be set during startup).

Compare current PLC program with a known working backup or reference project. Use Version Control tools in Automation Tool to identify any missing function calls or structural changes introduced during recent edits.