Resolving SINAMICS S110 CU305 PN Connection Failure in Starter V4.5.1.5

Starter V4.5.1.5 reports the SINAMICS S110 CU305 PN as a bus node with a question mark when the control unit ships with firmware 04.40.45. The drive was visible to DCP discovery but could not be accepted into the project, and a direct TCP/IP connection could not be opened. This article breaks the failure into its two independent root causes, then walks through the commissioning and recovery path used in the field, including a fallback to TIA Portal / Startdrive when the legacy Starter catalog cannot match the firmware.

1. Problem Statement

The reported failure is reproducible as follows:

• PC running Starter V4.5.1.5 with SSP SINAMICS V4.4 SP3 installed.
• Target hardware: SINAMICS S110 CU305 PN with firmware V4.4.45 (04.40.45), connected to the engineering PC via a direct Ethernet cable on the X150 P1/P2 PROFINET ports.
• Starter's accessible nodes view shows the S110 with a question mark overlay; the node cannot be accepted into the project tree.
• Online connection fails; the drive does not respond to standard TCP/IP commissioning attempts.

The "?" is a catalog miss, not a cable fault. Starter cannot match the device's reported firmware identity to any entry in the installed SSP, so it refuses to bind the device to a project slot. A second, independent fault is usually also present: the CU305 PN ships with PROFINET interface 1 set to 0.0.0.0, which prevents a TCP-based commissioning connection from being opened even when the device is identifiable.

2. Affected Hardware, Firmware, and Software

3. Root Cause Analysis

The reported fault is the visible symptom of two layered problems. Fix only one and the connection will still fail.

3.1 Default IP on the PROFINET interface

PROFINET interface 1 on a factory-fresh or recently reset CU305 PN has the IP address 0.0.0.0 and DHCP mode active. Starter performs a DCP identify-all broadcast, then opens a TCP connection to the discovered IP. With 0.0.0.0, no TCP socket can be established regardless of how the cable is wired. This is the same behavior the user observed: the node is visible (DCP success) but unreachable (TCP failure). Assigning a valid IP is a strict prerequisite.

3.2 SSP / firmware version mismatch

Starter's project tree is bound to the device catalog that ships inside the installed Support Package. The default SSP for Starter V4.5.1.5 is V4.4 SP3, whose highest supported firmware entry is 04.40.44.00. When Starter polls the drive, the drive announces FW 04.40.45. The catalog lookup returns no match, and Starter renders the device as a generic unknown PROFINET node with a "?". The fix is to either install a newer SSP that recognizes FW 04.40.45, or to switch to a commissioning tool that carries a newer device library (Startdrive).

3.3 Why downgrading is not recommended

Downgrading FW 04.40.45 to 04.40.44 will clear the catalog miss but it is a destructive operation: all saved parameters on the CF card / non-volatile memory are overwritten, motor data may need to be re-commissioned, and any safety-related parameters (e.g., Safety Integrated configurations) must be re-validated. Only fall back to a downgrade when the project is in factory state or all parameter backups are present.

4. Prerequisites

• Siemens engineering PC running Windows 10 / 11 (64-bit) with administrator rights.
• Starter V4.5.1.5 (or any 4.5.x / 4.4.x variant) installed locally.
• Siemens PRONETA (free) or SIMATIC Primary Setup Tool (PST) installed for IP assignment.
• Ethernet cable (Cat 5e or better) terminated to RJ45, with at least one crossover-capable port pair (most modern NICs auto-MDIX; direct cable works).
• PROFINET device name sticker on the S110, or read access via DCP.
• Optional: TIA Portal V14 SP1 or newer with the Startdrive option installed for the alternative path.
• Optional: SD card (1 GB+) with the SINAMICS FW 04.40.45 image if a downgrade is later required.

5. Pre-Connection Network Verification

1. Connect the engineering PC directly to X150 P1 of the CU305 PN. Disable all other network adapters (Wi-Fi, secondary LAN) to prevent DCP confusion.
2. Set the PC NIC to a fixed address in a private subnet, for example 192.168.0.10 / 255.255.255.0, with no gateway.
3. Open a command prompt and verify link: ping 192.168.0.10 -n 1 must return from the local interface. If it fails, replace the cable or the NIC.
4. Run arp -a to confirm no stale PROFINET entries exist; if the S110 was previously reachable on another IP, flush the ARP cache with netsh interface ip delete arpcache.
5. Disable Windows firewall temporarily on the private profile, or open UDP/34964 (DCP) and TCP/102 (S7 / SINAMICS RFC 1006) inbound and outbound. These two ports are sufficient for Starter commissioning.

6. Assigning a Valid IP Address to the CU305 PN

Use one of the three methods below. Method A is the fastest when only the S110 is on the bench.

6.1 Method A: PRONETA (recommended)

1. Launch PRONETA and switch to Network Analysis.
2. PRONETA lists every PROFINET device reachable via DCP. The S110 will appear as an unidentified node with MAC address, original device name (often blank), and current IP 0.0.0.0.
3. Right-click the S110 → Assign PROFINET name. Enter a name that matches the IO controller configuration, e.g. s110-cu305.
4. Right-click the S110 → Set IP address. Enter 192.168.0.20, subnet 255.255.255.0, no gateway.
5. Click Apply. The S110 reboots the PROFINET stack (about 5–10 s). PRONETA now shows the device as online with the assigned IP.

6.2 Method B: Direct STARTER parameter write (advanced)

If a different tool is already online (e.g., a PLC acting as IO controller), the IP can be assigned by writing to the drive's PN configuration parameters. This is also useful when the new IP must persist across power cycles.

After writing, activate with p8925 = 2 to commit, then perform a POWER ON of the CU305 PN. On the next boot the IP persists in non-volatile memory.

6.3 Method C: SIMATIC Manager / TIA Topology Editor

When the S110 is already part of a PROFINET IO system, the PLC project owns the name and IP. Open the device properties in HWCN / TIA Portal, navigate to PROFINET interface → Ethernet addresses, and assign both the PROFINET device name and the IP from the controller side. The PLC will push the configuration to the S110 on the next IO start.

7. Installing the Matching SSP for Starter

Starter's device catalog is built from Support Packages. To add FW 04.40.45, install a newer SSP that contains the corresponding SINAMICS V4.4 description file. The current SINAMICS V4.4 support package family is the correct branch for this firmware.

1. Download the latest SSP SINAMICS V4.4 (SP4 or SP5, depending on what is current) from the Siemens support portal under entry ID 109751275 (SINAMICS Support Packages overview).
2. Close Starter and the SINAMICS commissioning trace tools.
3. Run the SSP installer as administrator. The default path is C:\Program Files (x86)\Siemens\Automation\STARTER\SupportPackages.
4. Restart Starter. Open Help → Installed devices and confirm the entry SINAMICS S110 CU305 PN V4.4.x V04.40.45.00 (or the highest FW supported by the SSP) is listed.

8. Establishing the Starter Online Connection

1. Open Starter and open or create the project that targets the S110.
2. Right-click the drive → Target device → Accessible nodes.
3. Starter performs a DCP scan. The S110 should now appear with a green icon and a recognized catalog entry (no "?").
4. Highlight the device and click Accept. The S110 is bound to the project slot.
5. Right-click → Connect to target system. Starter opens the TCP connection to 192.168.0.20 on port 102 (S7 / RFC 1006).
6. After a successful connection, click Load HW configuration to target device to push the project offline image to the drive, then Load to PG/PC to read back the current parameter set.

9. Alternative Commissioning Path: TIA Portal / Startdrive

If an SSP for FW 04.40.45 is not available, switch to TIA Portal with the Startdrive option. Startdrive carries a continuously updated device library that already supports recent SINAMICS V4.4 firmware. The TIA path is also the strategic replacement for Starter for new projects.

1. Install TIA Portal V16 (or newer) with the Startdrive option.
2. Create a new project and add the S110 CU305 PN from the device catalog (search order number 6SL3040-1JA01-0AA0).
3. Open the device view, navigate to PROFINET interface → Ethernet addresses, and assign the device name s110-cu305 and IP 192.168.0.20.
4. Right-click the drive → Go online. Startdrive will identify FW 04.40.45 and download the matching device description automatically.
5. Use the Startdrive commissioning wizard to configure the motor (using the motor code on the rating plate), encoder, setpoint source, and telegram (Standard Telegram 1 for speed control, 2 for speed/torque, 3 for positioning with the FB POS of the technology object).

10. Verification and Online Diagnostics

Once the connection is established, run the following checks to confirm the drive is in a known-good state:

10.1 Inline connection state diagram

11. Firmware / SSP Compatibility Reference

12. Troubleshooting Matrix

13. Recommended Permanent Fix

1. Migrate the project to Startdrive in TIA Portal. Startdrive is the long-term commissioning tool and is the only path that follows the SINAMICS device library without manual SSP management.
2. Persist the IP and PROFINET name on the CU305 PN by writing p8920 / p8921 and committing with p8925 = 2, so the drive boots with a usable address even on a fresh PLC project.
3. Back up the S110 parameters to a CF card after every successful commissioning: in Starter / Startdrive, Copy RAM to ROM, then save the project to the card. This avoids the recurring catalog-miss problem when a support engineer reopens the drive months later with an older tool.

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