Resolving S7-400 PROFINET ET200S IM151 Naming and Ring Issues

Problem Overview

A PROFINET I/O network built around a SIMATIC S7-400 CPU 414-3 PN/DP (6ES7-414-3EM05-0AB0) experiences a hard bus fault as soon as a second ET 200S IM 151-3 PN HF (6ES7-151-3AA23-0AB0, firmware V6.0) is added to a SCALANCE X208 managed switch (6GK5-208-0BA10-2AA3). A single IM 151 connected through the X208 exchanges data without errors; the bus fault LED begins to blink and STEP 7 / TIA Portal goes offline against the IO devices the moment the second station is added. Recovery by MMC reset of the CPU does not bring the network back.

The browser-based web interface of the SCALANCE X208 continues to show all physical connections active, which proves the Layer-2 path is intact. The fault is therefore not a cabling or switch-port problem but a PROFINET identification conflict at the IO-device layer.

Affected Hardware and Firmware

Verify the controller and devices are on a release combination that the Siemens compatibility tool lists as approved; mismatch on PROFINET conformance class B / C is a frequent cause of intermittent station failures. Consult the Siemens PROFINET Commissioning and Diagnostics manual for the minimum firmware matrix.

Root Cause Analysis

Three interacting root causes are typical in this configuration. Any one of them will reproduce the symptom.

1. Duplicate PROFINET device name. PROFINET IO uses the PROFINET station name (max 240 characters, label set defined in IEC 61784-2) as the primary identity of an IO device. If both IM 151 stations carry the factory default name (e.g. im151-3pn) or the same name assigned during a prior single-station test, the controller raises a name conflict and refuses AR (Application Relationship) establishment with both devices.
2. Missing SCALANCE X208 in HW Config. The X208 is a PROFINET-capable managed switch. It must be present in the STEP 7 / TIA topology either as a PN device (its GSD file GSDML-Vx.x-Siemens-SCALANCE_X208-...) or as a partner port in the topology editor. Without it, the controller has no port interconnection data and any name assignment on devices beyond the first switch port cannot be tracked by the controller during AR setup.
3. MRP ring not closed or roles undefined. The phrase "you trying to ring?" is the operative clue: the cable is almost certainly forming a ring between the two PN ports of the CPU and the SCALANCE X208 with the two IM 151 stations as ring members. MRP (Media Redundancy Protocol per IEC 62439-2) requires exactly one Manager (MRM) and one or more Clients (MRC). When roles are unspecified, the IM 151 stations default to MRC, but if the controller's PN interface is set to "not MRP-capable" while the rest of the ring expects MRP, the ring stays open and PROFINET diagnostic frames time out, producing the bus fault.

PROFINET IO Device Naming Fundamentals

PROFINET IO devices identify themselves to the controller through the PROFINET device name (also called station name or PNIO name). The name is stored in the device and is assigned by the engineering tool (STEP 7 V5.x: Target system > Ethernet > Assign PROFINET device name; TIA Portal: Online > Device maintenance > Assign PROFINET device name). Assignment is performed using the DCP (Discovery and Configuration Protocol) multicast frame described in IEC 61784-2.

Rules that must be observed:

• Name length: 1 to 240 octets.
• Allowed characters: letters a..z, A..Z, digits 0..9, hyphen -, period .. The first character must be a letter. The name must not end in a hyphen.
• Each IO device in a controller's AR list must have a unique name. The controller matches the configured name against the DCP Identify response from the device.
• Two devices sharing a name will each fail AR establishment; the controller will report "Station failure" or "Device name not unique" in the diagnostic buffer (event IDs 0x001E, 0x001F in STEP 7).

See the PROFINET Addressing and Naming application note for the complete character set and DCP frame format.

Pre-Diagnostic Steps

1. Connect a programming device (PG) to port 1 of the SCALANCE X208 (management port on the front of the unit). Confirm the PG obtains a link and a valid IP in the same subnet as the CPU's PN interface.
2. Open a browser and navigate to https://<switch-ip> (default IP of the X208 is 192.168.0.1, user admin, password admin on a virgin device). Verify under Information > ARP Table that all three PROFINET nodes (CPU PN port, IM 151 #1, IM 151 #2) appear with their MAC addresses. If any node is missing, resolve the physical layer first.
3. Open STEP 7 (or TIA Portal) and read the CPU's diagnostic buffer. Capture every event ID with timestamp and OB number. Event ID 0x001E indicates "PROFINET IO station failure", 0x001F indicates "PROFINET IO station return". Event ID 0x010C indicates "PROFINET interface: name conflict".
4. From the PG, open Online > Accessible Nodes. The X208 should appear. Each IM 151 should appear with its current PROFINET name and IP. Compare the name of IM 151 #1 and IM 151 #2 — if identical, the conflict is confirmed.
5. Power down all three PN nodes. Disconnect the ring cable between the CPU's PN port and port 1 of the X208. Power up only the CPU and IM 151 #1 (direct connection, no switch). This is the "first configuration" that the original installer reported as working; it is the reference state.

Resolution 1: Assign Unique PROFINET Device Names

The single most common cause of the bus fault in this topology is identical PROFINET names on the two IM 151 stations. Restore unique names with the following procedure.

1. In STEP 7 HW Config (or TIA Portal device view), select the first IM 151 and open Properties > PROFINET interface > Ethernet addresses. Enter a name that follows the naming convention of your plant, for example et200s-line1 and IP 192.168.0.11 / mask 255.255.255.0.
2. Repeat for the second IM 151 with a distinct name, e.g. et200s-line2 and IP 192.168.0.12.
3. Compile and download the HW Config to the CPU. Do not yet power on the second IM 151.
4. From HW Config, right-click the first IM 151 and choose PLC > Assign PROFINET device name. In the dialog select the visible IM 151 by MAC address and click Assign name. Confirm with the LED flash (IM 151 blinks the LINK/Activity LED of port 1 when it is selected).
5. Repeat for the second IM 151 using its unique name. The assignment is written to non-volatile memory inside the IM 151 and survives power cycles.
6. Power the second IM 151. The CPU should now establish AR with both stations; the BF LED on the CPU's PN interface should extinguish within 2-3 update cycles (default update time 1 ms, so within ~3 ms plus AR setup time).

Resolution 2: Integrate the SCALANCE X208 in the Topology

A managed PROFINET switch is a true PROFINET device and must be known to the IO controller. The X208 supports both a GSD-based integration and integration via the topology editor. Choose one of the two methods below.

Method A — GSD-based integration (recommended for STEP 7 V5.x)

1. Install the GSD file for the X208 from the SCALANCE X208 product support page (look under Downloads > GSD files).
2. In HW Config open the catalog, navigate to PROFINET IO > Network components > SCALANCE X-200, and drag the X208 onto the PROFINET IO system of the CPU.
3. Assign the switch a PROFINET device name, e.g. sw-line1 and IP 192.168.0.2.
4. Draw the port interconnections: CPU PN port 1 ↔ X208 port 1, IM 151 #1 ↔ X208 port 2, IM 151 #2 ↔ X208 port 3, X208 port 7 (ring port 1) ↔ CPU PN port 2 (ring port 2).
5. Compile, download, and use Assign PROFINET device name on the X208 itself.

Method B — Topology editor (TIA Portal V14 and later)

1. Open the Topology view in the TIA Portal project tree.
2. Drag the X208 from the catalog onto the topology. Right-click the devices and select Add port interconnection to define the cabling as it physically exists on the plant floor.
3. The TIA compiler then checks the configured topology against the live topology read at runtime via LLDP. Any mismatch (wrong port, swapped cable, missing partner) is reported as a diagnostic alarm of severity "maintenance required".

MRP Ring Configuration

The ring topology that triggers this report (CPU PN port 1 → X208 port 1 → X208 → IM 151s → back to CPU PN port 2 → X208 port 7) is a classic PROFINET MRP ring. The configuration must be explicit.

1. Open the Properties of the CPU's PROFINET interface. On the Media Redundancy tab select MRP Manager and set the Role to Manager. The CPU becomes the MRM.
2. Set the ring ports explicitly: port 1 = ring port 1, port 2 = ring port 2. The CPU blocks all other frames on these ports during the redundancy test, which happens every 50 ms by default.
3. For the SCALANCE X208 open Properties > Media Redundancy and set the role to MRP Client (MRC). The X208 has two ring ports (configurable, default ports 1 and 7 on the 6GK5-208-0BA10-2AA3) that forward frames only when the manager permits.
4. For each IM 151-3 PN HF, on the Media Redundancy tab select MRP Client. The two ring ports of each IM 151 are its PN port 1 and PN port 2 (the IM 151-3 PN HF has an integrated 2-port switch).
5. Maximum ring reconfiguration time per IEC 62439-2 is 500 ms. With four MRCs and one MRM the typical reconfiguration in a Siemens MRP ring is below 200 ms. If you require shorter reconfiguration, upgrade the ring to MRPD (MRP with cut-through), but this requires PROFINET conformance class C and firmware V2.3 or higher on all devices.

Reference: ET 200S IM 151-3 PN HF manual (chapter on media redundancy) and the S7-400 CPU 414-3 PN/DP manual.

Verification Checklist

Troubleshooting Matrix

Advanced Diagnostics

If the network remains unstable after the above, escalate with the following toolset.

1. SIMATIC Automation Tool — use the "Network analysis" function to scan the PROFINET network and report all station names, IPs, and device roles.
2. PRONETA (free Siemens tool, download at the PRONETA product page) — provides a graphical topology view, executes an IO test, and exports the network configuration. PRONETA can also reset a device's PROFINET name and IP without an engineering station.
3. Wireshark with PROFINET dissector — capture on a mirror port of the X208 (port 7, set as "Mirror port" via the Web server). Filter on pn_dcp and pn_io. Verify the DCP Identify requests from the CPU (source MAC = CPU PN port) and the responses with the device name. Duplicate names show up as two DCP Identify responses with the same name from different MACs.
4. SCALANCE X208 Web server > Information > Event log — check for "Topology change", "Ring open", or "MRP timeout" events. Each event carries a timestamp and the affected port.

Resetting Components for a Fresh Start

The original poster asked for a procedure to "initialize components to restart testing". Use the following sequence.

1. CPU 414-3 PN/DP: Power off. Insert the MMC into a PG, format it with the PG (STEP 7: File > S7 Memory Card > Format). Reinsert, power on. The CPU performs a factory reset, clearing the PROFINET device name table.
2. IM 151-3 PN HF: Power off. Hold down the "MRES" button on the front of the head module. Power on while holding MRES for at least 10 seconds. The BF and SF LEDs flash alternately; release MRES. The PROFINET name is reset to the factory default im151-3pn and the IP is cleared. (See the IM 151-3 PN HF manual for the exact button sequence.)
3. SCALANCE X208: Use the Web server System > Reset > Reset to factory settings or, in the absence of an IP, use the SET button on the front panel (hold during power-up for 10 seconds) to restore 192.168.0.1 with default credentials.
4. After the three resets, reassign the names and IPs according to Resolution 1 above.

FAQ