Troubleshooting ET200SP Remote I/O Communication with ET200S CPU

ET200S IM151-8 PN/DP controllers fail to exchange process data with ET200SP IM155-6 PN stations when BaseUnit color coding, slot mapping, or PROFINET device-name assignment does not match the TIA Portal hardware catalog. This field guide documents the diagnostic pattern—RN LED blinking on the IM and Diag LED blinking on every I/O module—and the deterministic resolution path verified on a four-station distributed I/O network programmed in TIA Portal V11.

1. Problem Statement and Diagnostic Symptom

A SIMATIC ET200S-based controller (CPU 6ES7 151-8AB01-0AB0) is configured as PROFINET IO controller with four ET200SP stations (IM 6ES7 155-6AU00-0BN0) acting as distributed I/O. After the hardware is wired and the TIA Portal V11 project is loaded, the controller cannot establish cyclic data exchange with any of the four remote stations.

Observed LED state on every IM155-6 PN:

• LED RN (RUN) is blinking green at ~2 Hz
• LED ER is off
• LED MAINT is off
• LED LK1 or LK2 is on (physical link present)
• LED PWR is solid green

Observed LED state on every I/O module:

• LED Diag is blinking at ~0.5 Hz

This state matches the Siemens diagnostic pattern "station in commissioning / parameter assignment error." The PROFINET connection is physically present (LK lit), but the controller is unable to finish parameter assignment to the slots. Because the symptom appears on all four stations simultaneously, treat the issue as project-wide (TIA Portal configuration) before assuming a per-station hardware fault.

2. Reference Hardware Configuration

The original system uses the following catalog numbers, recorded for cross-reference against TIA Portal hardware catalog entries. Verify every MLFB before commissioning—Siemens re-revisions modules frequently and a V11-era project may not contain the latest article number.

Main panel (ET200S, slot 1 = CPU):

Remote I/O 1–4 (ET200SP, each starts with one IM):

Compare against the current SIMATIC ET 200SP catalog and product overview when verifying module revisions. The IM155-6AU00-0BN0 is the standard (ST) PROFINET interface, not the high-feature (HF) variant. If your project enables HF-only features (shared device, S2 system redundancy, MRP manager, iPAR server), the configured IM is wrong and the station will reject parameter assignment even with valid slots.

3. LED Diagnostic Reference for IM155-6 PN

The IM155-6AU00-0BN0 has four status LEDs (PWR, RN, ER, MAINT) plus two link LEDs (LK1, LK2). Use the following table to decode observed LED states:

The I/O module Diag LED uses the same pattern:

• Off: module OK, parameter assignment complete
• Flashing ~0.5 Hz: module in commissioning state or diagnostic pending (the IM has not finished parameter assignment for this slot)
• On red: module fault, channel fault, or parameter error (this module specifically failed)

The combined pattern of "RN blinking on IM + Diag blinking on every I/O module" points to a station-wide parameter-assignment error, not an individual module failure. When the cause is a single bad slot, only that module's Diag LED is on solid; the others stay off. Station-wide flashing indicates a structural issue at the IM or the load-group level.

4. Root Cause Catalog

When the symptom set above appears on all four remote stations simultaneously, the most probable causes are ranked by field frequency:

1. BaseUnit color-coding mismatch (white BaseUnit placed where dark grey is required, or vice versa). Most common field error when migrating from ET200S-style terminal blocks to ET200SP BaseUnits.
2. PROFINET device name not assigned to the IM155-6. The controller cannot establish an Application Relationship (AR) without a matching name, and the IM stays in the "blinking RN" state indefinitely.
3. Slot / empty-slot configuration mismatch. A slot is occupied in TIA Portal but empty in the real rack, or the real slot is filled with a different module type or order than the project shows.
4. Firmware update in progress. The IM and I/O modules flash in sequence during a station-wide firmware update; this is normal behavior and resolves on its own after 2–10 minutes.
5. GSDML file revision mismatch. The HW catalog in TIA Portal V11 may not contain the exact firmware revision of the physical module, and the wrong version is being loaded—producing a "module does not match expected type" diagnostic event.
6. Power supply sequencing. The 24 V load voltage (L+) is missing on the first BaseUnit of a load group, or the dark/light BaseUnit wiring is inverted (L+ on the wrong terminal).
7. Watchdog time too short. If the project sets a PROFINET watchdog of 1–3 ms but the controller and four stations cannot complete the parameter handshake in that window, the controller aborts the AR and reports the IM as failed.
8. Shared-input / shared-output misconfiguration. The ST variant of IM155-6 does not support shared device. If the project imports HF parameters from a GSDML, the IM rejects them.

If the same symptom appears on all four stations, treat the issue as project-wide (TIA Portal configuration) before checking per-station hardware. Begin with the most common cause (BaseUnit color) and work down the list.

5. BaseUnit Color Coding and Load-Group Construction

ET200SP BaseUnits (BU) are mechanically and electrically distinct. The physical color of the spring-release bar encodes the load-group role:

• White (light) release bar: BU type A0, B0, C0, D0. Starts a new load group. Provides a new feed-in path for 24 V L+ and 24 V AUX. The first BaseUnit to the right of the IM155-6 must be white.
• Dark grey release bar: BU type A1, B1, C1, D1. Passes the L+ supply through to the next module. Does not start a new load group. Used for slot gaps and mid-group positions.

The electronic coding of the BaseUnit (the white plastic key on the left side of each BU) is read by the I/O module at insertion. If the I/O module expects a "with AUX" or "with infeed" BaseUnit but the physical slot has a "pass-through" BaseUnit, the module reports a configuration error. TIA Portal V11 enforces this; if the project has a different BU type than the physical rack, the offline/online compare shows a yellow conflict on that slot.

Verification in TIA Portal:

1. Open Devices & Networks, click the ET200SP station.
2. Right-click the BaseUnit in the device view, choose Properties.
3. On the General tab, confirm the BU type matches the physical BaseUnit's part number (printed on the side label).
4. On the Potential group tab, confirm "New potential group" is checked only on the first white BaseUnit after the IM. All other BaseUnits in the station must show "Continue potential group."
5. Compile the project (Project → Compile all) and verify the device view shows no yellow or red conflict markers.

6. System Topology and PROFINET Addressing

The four ET200SP stations hang off the PROFINET port of the ET200S CPU through a managed switch. The typical commissioning topology is:

Addressing scheme for the four ET200SP stations:

The IP address is assigned automatically by the controller during the AR setup; you only need to assign the device name. The IM155-6 stores the name in non-volatile memory and retains it across power cycles.

7. Step-by-Step Resolution Procedure

Apply the steps in this order. Each step is independent; if a step's check passes, move to the next.

1. Power down all four ET200SP stations to clear the IM diagnostic state.
2. Compare each physical slot's BaseUnit part number against the TIA Portal device view. Replace any mismatched BaseUnit (white vs. dark grey, or A0 vs. B0 mismatch).
3. Open TIA Portal, select the ET200SP station, and check the Potential group of every BaseUnit. Only the first white BaseUnit to the right of the IM should have "New potential group" enabled. All subsequent white BaseUnits must be changed to "Continue potential group."
4. Compile the project (Project → Compile all) and verify the device view shows no yellow or red conflict markers on any slot.
5. Download the hardware configuration to the ET200S CPU (Online → Download to device). Confirm the CPU is in STOP, or stop it manually if the controller permits online download.
6. Open Online → Accessible Nodes, confirm all four IM155-6 stations appear with their MAC addresses. The MAC is printed on the front of each IM. If a station is missing, check the Ethernet cable and switch port.
7. Assign PROFINET device names to each station. Verify the name assigned in the dialog matches the name in the project exactly (case-sensitive). For a four-station project, you can also use the PRONETA tool to assign names in batch via a CSV import.
8. Power cycle each ET200SP station. The RN LED should transition: blinking → solid green within 5–10 seconds. The I/O module Diag LEDs should go off.
9. If RN is still blinking after power cycle, repeat step 7 with PRONETA to confirm DCP discovery succeeds. Open the controller's diagnostic buffer; a persistent "station failure" entry indicates a GSDML or hardware revision mismatch.
10. If the I/O module Diag LED is still flashing but the IM RN is solid green, compare the slot mapping. The most common cause is a wrong module order, a missing module between two placed modules, or a wrong BU type on a specific slot.
11. Verify cyclic data exchange by forcing a sensor input and observing the corresponding process image bit in the CPU. The I/O area is mapped according to the slot order in TIA Portal; document the I-address and Q-address ranges in the project notes.

8. Firmware Update Sequence and Timing

The IM155-6 supports field firmware update via TIA Portal (Online → Firmware update) or via SIMATIC Automation Tool. When a station-wide update runs, the timing sequence is:

Expected durations for the module set in this project:

• IM155-6AU00 firmware: 60–120 s
• DQ 16×24 V (6ES7 132-6BH00-0BA0): 30–60 s per module
• AI 4×U/I (6ES7 134-6DH00-0BA1): 30–60 s per module

Total expected time per station: 2–4 minutes for this configuration. If the RN LED continues to blink beyond 10 minutes with no progress indication, the update has stalled. Power-cycle the station and re-attempt the update from the TIA Portal Online menu. If the module is non-responsive, the SIMATIC Automation Tool can recover the IM by forcing a firmware downgrade through the TIA Portal "Update firmware" wizard.

9. TIA Portal V11 Configuration Caveats

TIA Portal V11 was released in 2012 and predates many current ET200SP module revisions. Known issues with V11 against modern IM155-6 hardware:

• HW catalog age: the V11 catalog may not contain the latest MLFB. Use "Update catalog" or import the GSDML file from the Siemens support portal before commissioning.
• Parameter dialog reduction: module parameter dialogs in V11 may show fewer options than the module supports. Parameters set in V14/V15 may not be editable when the project is re-opened in V11.
• IM155-6 firmware compatibility: the IM155-6 PN ST (6ES7 155-6AU00-0BN0) firmware V3.x is the first revision fully supported in TIA Portal V11 SP2 Update 5. Earlier V11 service packs may reject the device entirely.
• GSDML import: when importing a GSDML for a module not in the V11 HW catalog, place the GSDML file under C:\Program Files\Siemens\Automation\Portal V11\Data\Hsp\ and restart TIA Portal.
• Project portability: TIA Portal V11 projects can be opened in V13 SP1 or later, but the device view may be silently re-numbered on upgrade. Always recompile and verify slot mapping after any portal upgrade.

If a project upgrade to TIA Portal V14 or later is feasible, do so. The diagnostic buffer, online compare, and PRONETA integration are significantly improved in newer releases. The V11 release is past its support window and Siemens no longer provides SP updates for it.

10. Verification Checklist

After applying the resolution, confirm the following with TIA Portal online diagnostics and visual inspection:

11. Troubleshooting Matrix

12. Resolution Flowchart

13. Cross-Platform and Migration Notes

The same diagnostic pattern appears on other Siemens controller families pairing with ET200SP, including S7-1500 CPU 1511/1515/1516 and S7-1200 CPU 1215C/1217C. The IM155-6 PN ST behaves identically regardless of controller. The HF variant (6ES7 155-6AU01-0BN0) adds shared device, S2 redundancy, and MRP client features; if the project is migrated from ST to HF, the HW catalog entry and any HF-only parameters must be updated.

For projects where the ET200S CPU is being replaced with an S7-1500, port the TIA Portal V11 project into V15 or V16 first. The ET200S CPU 151-8AB01 is end-of-life and spare-part supply is constrained. When porting, the ET200S-specific modules (PM-E 6ES7 138-4CA01) require a one-to-one replacement with an ET200SP PM or removal from the slot table.

For brownfield projects where the IM155-6 firmware is older than V3.0, upgrade the IM firmware before commissioning. The V3.0 firmware adds S2 system redundancy support and improved diagnostic buffer depth, both of which simplify field troubleshooting.

14. FAQ