SINAMICS G120C PN Not Assigned in TIA Portal: PROFINET Name Fix

The combination of a SINAMICS G120C PN drive and a SIMATIC S7-1200 in TIA Portal is one of the most common low-voltage variable-speed setups in machine building. The first-time commissioning flow almost always runs into the same wall: the drive icon in the topology view persistently shows Not assigned, the controller offer dialog stays empty, and a flashing red BF LED on the front of the Control Unit indicates that no PROFINET AR (Application Relationship) has been established. This article walks through the underlying DCP (Discovery and Configuration Protocol) naming principle, the firmware constraints on the S7-1200, and the exact sequence of TIA Portal operations that resolves the symptom without replacing hardware.

Problem Description

When commissioning a G120C PN with a SIMATIC S7-1200 in TIA Portal V13 or later, the drive frequently appears in the device diagnostics view with the status Not Assigned and the BF (Bus Fault) LED on the Control Unit front cover flashes red at approximately 2 Hz. The drive does not appear under any IO-Controller in the Devices & Networks topology editor, and the standard automatic assignment when entering online detection fails because no PROFINET controller is offered in the selection dialog.

The symptom is identical for both a fresh project (drive still carries a factory-default PROFINET name) and for a previously commissioned unit that has been re-imported into a new project. The PLC and drive are on the same subnet and respond to ping from the engineering station, which confirms Layer 1 (electrical) and Layer 3 (IP) reachability but does not confirm Layer 2 PROFINET station-name resolution.

Root Cause Analysis

PROFINET IO uses a station-name-based discovery mechanism defined in IEC 61784-2 and transported by DCP. Before the IO-Controller can establish an AR with the IO-Device, the IO-Device must carry a PROFINET device-name string in its non-volatile memory that exactly matches the device name declared for that node in the engineering tool's IO-Device configuration. The IO-Controller also requires a unique device name that is allowed to differ from the IO-Device name; it identifies the PLC side of the AR.

The field-failure pattern that produces the "Not assigned" state on a G120C PN when paired with an S7-1200 falls into one of the following root-cause buckets:

1. Device-name mismatch. The PROFINET device name stored inside the G120C PN (written by the previous project, by another engineering station, or by the unit's factory profile) does not match the name entered for the IO-Device in the TIA Portal device configuration. The TIA Portal Assign PROFINET device name function compares names case-sensitively. The most common operator error is to type the name of the PLC into the G120C's name field of the topology editor, or vice-versa, leaving the two stations unable to recognise each other.
2. PLC firmware too old for IO-Controller role. An S7-1200 with firmware V1.0 cannot act as a PROFINET IO-Controller. Only firmware V2.0 and later support the PROFINET IO-Controller role. A CPU with the older firmware appears in the project, compiles cleanly, but will not expose itself as a controller in the device list, and the drive will be unable to find any controller to attach to.
3. TIA Portal version mismatch. TIA Portal V13 SP1 is the minimum that fully supports the SINAMICS G120C PN HSP (Hardware Support Package) used by early G120C PN units. TIA Portal V13 without the matching HSP, or TIA Portal V14 with an outdated GSD file, may show the device but leave the IO configuration incomplete, producing the same "Not assigned" message.
4. Wrong device family selected. Inserting a non-PROFINET G120C variant (USS, Modbus, or PROFIBUS G120C) while wiring PROFINET will not produce a controller assignment; TIA Portal will not allow IO assignment at all because the device family declares no PROFINET interface.
5. Subnet or interface mismatch. The PLC and drive are placed in different PROFINET subnets in the topology editor and therefore fall into different broadcast domains; DCP discovery cannot cross routers. This is also the most common outcome of mistakenly typing the name of the drive into the PROFINET device name field of the PLC, leaving the PLC with no name on its own interface.

Affected Hardware and Firmware

Verify the PLC firmware with Online > Diagnostics > CPU operating mode in TIA Portal or by reading the value of the MMC. Verify the SINAMICS firmware with parameter r0018 in the parameter list, the BOP-2 / IOP, or the SD-card nameplate printed on the Control Unit cover. The order of checks matters: a wrong PLC firmware is resolved by update, a wrong drive firmware by parameter download or SD-card update — never by re-naming.

Prerequisites

Confirm each item before changing the configuration. Skipping checks is the most common reason the symptom re-appears after a fix.

1. The S7-1200 firmware is V2.0 or higher. If the firmware is V1.0, perform a firmware update using a SIMATIC Memory Card (SMC) with at least 4 MB free and the matching *.upd file from the Siemens support portal. The PLC must be in STOP during the update.
2. The G120C PN has been commissioned to the point where it accelerates an unloaded motor in JOG mode from the BOP-2 (Basic Operator Panel). If JOG is impossible, a separate commissioning issue (motor data, ramp, 24 V enable) blocks the motion regardless of PROFINET.
3. The engineering station and the PLC are on the same physical Ethernet segment as the drive, with no Layer-3 router required. If a router is unavoidable, enable DCP relay (LLDP) forwarding on the switch.
4. The S7-1200 PROFINET interface and the G120C PN are configured in the same PROFINET subnet in the TIA Portal topology editor. Verify by selecting the line connecting the two devices and checking the subnet property — both must read PN/IE_1.
5. TIA Portal has been started "as administrator" (Windows UAC elevation) when loading the G120C PN HSP for the first time, otherwise the GSD file is not registered correctly.
6. The Windows firewall on the engineering PC allows UDP port 34964 (DCP discovery) and UDP port 34963 (DCP identification). On locked-down corporate PCs, temporarily disable the firewall for the test.

Step-by-Step Resolution

1. Open Devices & Networks. In the TIA Portal project tree, double-click Devices & Networks. The network view should display the S7-1200 PLC_1 on the left and the G120C PN on the right with a coloured line connecting them. If no line exists, drag from the PLC PROFINET port to the G120C PN to create the topology link.
2. Inspect the controller offer for the G120C PN. Click the G120C PN. In the lower Properties pane, open PROFINET interface > PROFINET device name. If the field shows a value different from what is stored in the physical drive (read with the web server, parameter r6500), this confirms a mismatch.
3. Select the controller in the topology. Click the G120C PN icon. The status bar should show Not assigned to any IO controller. Right-click the device and choose Assign to new IO controller. If a line to PLC_1 already exists, click directly on the line and pick Assign IO controller > PLC_1.PROFINET_1.
4. Confirm the device name. When prompted, accept the prompt to assign the PROFINET device name to the device. TIA Portal issues a DCP Identify frame (matched against the current MAC) followed by a DCP Set frame with the desired name. The drive stores the new name in non-volatile memory and reboots its PROFINET stack in approximately 5 s.
5. Set the PLC PROFINET name correctly. In the PLC properties, open PROFINET interface > Ethernet addresses and verify the PROFINET device name. A reasonable choice is plc1 or cpu1214c. Do not type the name of the G120C PN in this field, and do not leave it blank if the network policy requires a name. This is the exact mistake that produced the original symptom.
6. Compile and download. Right-click PLC_1 > Compile > Hardware (rebuild all) > Download to device. Choose PN/IE_1 as the interface and the PLC's IP address as the target. Once the PLC is in RUN, the BF LED on the G120C PN extinguishes and the AR is established.
7. Read the assignment in online mode. Click the G120C PN, then Online > Online and diagnostics. The PROFINET diagnostics tab shows the IO-Controller reference. The status field should now read the PLC's PROFINET device name and IP.

Alternative PROFINET Naming Methods

If the Assign PROFINET device name dialog in TIA Portal does not complete (for example, the firewall blocks DCP multicast 239.255.255.255, or the engineering PC has multiple active network adapters), use one of the following alternatives.

Method 2a: Web server of the G120C PN

1. Set the engineering PC to a fixed IP in the same subnet as the drive's default IP 192.168.0.32 / 255.255.255.0 (factory-default Control Unit address).
2. Open the SINAMICS web server in a browser at http://192.168.0.32.
3. Navigate to Parameters > Communication > PROFINET.
4. Enter the exact device name that TIA Portal is configured to expect and click Set Values.
5. Power-cycle the drive's Control Unit for the name to take effect from cold start.

Method 2b: PRONETA (network analysis tool)

Siemens provides the free PRONETA tool for IO testing and PROFINET commissioning. Launch PRONETA, scan the network, identify the G120C by its MAC address (printed on the front label), and use the Assign PROFINET device name action. PRONETA is the fastest method when multiple identical drives are present and cannot be told apart by DCP name yet.

Method 2c: SIMATIC Automation Tool

The SIMATIC Automation Tool can assign PROFINET names in batch from a CSV. This is helpful for series commissioning of multiple G120C PN units with a reproducible naming convention such as g120c_pn_01, g120c_pn_02, ...

Verification

Troubleshooting Matrix

Configuration Reference for a Working Project

Related Drive Commissioning Considerations

Restoring PROFINET assignment alone will not turn the motor. The G120C PN needs its drive-side commissioning finalised: motor data set (p0300 – p0311), application macro (p0015), control mode (p1300), ramp times (p1120, p1121), and command source (p0700 = 6 for PROFINET).

With the standard telegram 1 in place, the PLC controls ON/OFF via control word bit 0 (ON/OFF1) and bit 1 (OFF2). The ramp function generator receives the speed setpoint via PZD 2. Confirm the drive accepts an enable from the PLC by setting p0850[0] to 722.0 (BI: Control word 1, word 0, bit 0) and clearing all faults with p3981 = 1. Read the active commissioning macro from r3996.

If STARTER is used instead of Startdrive, the same parameters apply. The factory-default macro of the G120C PN when delivered is typically Standard I/O with analog setpoint (no PROFINET). On first power-up the firmware auto-selects the fieldbus macro only if PROFINET is detected as the wired interface — otherwise the macro must be changed manually.

Field Tips for Series Commissioning

• Adopt a single naming pattern from day one: g120c_pn_NN where NN is a zero-padded index. Write the chosen name on a sticky label on the Control Unit so the field service engineer does not have to read the SD card to know what the drive believes it is called.
• Configure Identification and Maintenance (I&M) data on the drive (parameters p8806[0..4]) and enter the same values into the TIA Portal I&M view. This lets you locate a drive in the network by serial number or by plant location tag.
• Enable the diagnostic interrupt on the drive slot in TIA Portal, so a PROFINET fault generates a PLC OB82 call. The OB82 can be left empty initially and is the cleanest place to forward drive faults to a global HMI alarm.
• For multi-drive cabinets, reserve PROFINET names per slot using a shared Excel spreadsheet and have PRONETA or the SIMATIC Automation Tool load the CSV during commissioning. Naming errors are the most common source of "the wrong axis moves" calls during field service.
• Always download the SINAMICS drive project (Startdrive) AFTER the PLC hardware config. The drive requires the host PLC to be in RUN for online diagnostics to populate, even if the basic AR was established while the PLC was in STOP.

Frequently Asked Questions