C135 PCS 7 (PCS7)
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Troubleshooting SIMATIC PDM Online Communication Errors on Foundation Fieldbus Segments

Troubleshooting SIMATIC PDM Online Communication Errors on Foundation Fieldbus Segments

When SIMATIC Process Device Manager (PDM) fails to connect online to field instruments or the bus interface module (IM 655-5FF) on a Foundation Fieldbus (FF) segment—posting the error An error occurred during communication while cyclic process values update normally in CFC and WinCC—the issue is caused by misconfigured PDM communication routing, mismatched FF H1 communication parameters, or missing Electronic Device Description (EDD) libraries. Cyclic process data flows via deterministic controller I/O telegrams over PROFINET, whereas PDM uses acyclic dataset routing (record data transfers) routed through the controller's communication stack. To restore PDM connectivity, verify acyclic routing in SIMATIC PDM Network View, ensure the Compact FF Link firmware is updated, and reassign the communication path.

Table of Contents

Cyclic vs. Acyclic Communication Architecture on Foundation Fieldbus

In SIMATIC PCS 7, integration of Foundation Fieldbus (FF H1) instrumentation involves two parallel communication pathways:
- Cyclic Process Data (Deterministic): Measurement values (PV), valve positions, and NAMUR signal status bytes (ST) are polled cyclically by the S7-410 controller over PROFINET and the Compact FF Link (IM 655-5FF). This data executes within the controller's OB35 interrupt scan.
- Acyclic Engineering Data (On-Demand): Calibration parameters, transmitter diagnostics, device setup menus, and sensor curves are managed exclusively by SIMATIC PDM. PDM transmits acyclic read/write record datasets through the S7 CPU's diagnostic routing channel down to the FF H1 segment.
- The Divergence: A physical or configuration failure in the acyclic routing pathway leaves cyclic I/O updating with "Good" quality code while completely severing PDM engineering communication.

Why Cyclic CFC Values Work While PDM Online Fails

When an engineer observes healthy live process values in CFC but receives An error occurred during communication in PDM:
1. PROFINET S2 Cyclic Channel Healthy: The PROFINET link between the CPU 410-5H and the IM 655-5FF interface module is operating normally, satisfying cyclic telegram exchanges.
2. Acyclic Gateway Routing Blocked: To reach the FF H1 field devices, PDM requires the controller to act as an S7 router using acyclic DS100/DS101 records.
3. Common Roadblocks:
- The PDM communication path was assigned to the wrong network interface (e.g., mapped to an isolated plant bus instead of the routing CPU).
- The FF Link's internal acyclic buffer is locked due to an unclosed diagnostic session.
- The Electronic Device Description (EDD) installed in PDM does not match the exact hardware and firmware revision of the field transmitter.

The Role of Compact FF Link (IM 655-5FF) and Fieldbus Couplers

The SIMATIC Compact FF Link (6ES7 655-5FF00-0AB0) acts as the protocol converter between redundant PROFINET IO and Foundation Fieldbus H1:
* Upstream: Redundant PROFINET IO connections (System Redundancy S2).
* Downstream: Foundation Fieldbus H1 segment operating at 31.25 kbps with integrated fieldbus power supply and physical layer diagnostics.
* If one segment communicates while another segment fails, the issue is isolated either to the specific IM 655-5FF module, lower-layer bus termination, or the PDM network assignment for that second segment.

Method: Step-by-Step PDM Communication Route Recovery

Follow this troubleshooting procedure to restore online PDM communication:

Step 1: Verify the PDM Network View Configuration

  1. In SIMATIC Manager, switch to the Process Device Network View (or open SIMATIC PDM from the Windows Start menu).
  2. Expand the network hierarchy:
    Networks -> PROFINET IO -> CPU 410 -> IM 655-5FF -> FF H1 Segment.
  3. Verify that all field devices under the affected segment appear under the correct segment node.
  4. If the device was inserted manually into the Plant View without proper network linking, right-click the device and select Object Properties -> Communication Path:
    - Ensure the path points to the active CPU 410-5H and the correct PROFINET interface.

Step 2: Check EDD Device Description Assignment

  1. In SIMATIC PDM Network View, right-click the failing field transmitter and select Open Object.
  2. If PDM fails with a device description error:
    - Close PDM.
    - Open the Device Integration Manager (DIM) in SIMATIC PDM.
    - Verify that the Foundation Fieldbus Device Library is installed.
    - Import the vendor-certified EDD file matching the transmitter's device type and revision.
  3. In PDM, right-click the device, select Assign Device Type..., and assign the matching EDD descriptor.

Step 3: Clear Module Communication Locks on IM 655-5FF

  1. Open HW Config for the station hosting the Compact FF Link.
  2. Go online (Station -> Open Online).
  3. Select the IM 655-5FF module on the failing segment and choose PLC -> Module Information.
  4. Check the Diagnostic Buffer tab:
    - Check for acyclic buffer overflow events or FF H1 token circulation timeouts.
  5. If communication is hung, cycle power to the specific IM 655-5FF interface module (or execute a warm restart via HW Config online).

Step 4: Re-establish Online Connection in PDM

  1. Return to the PDM Process Device Network View.
  2. Select the field device, right-click, and select Start Device - Online.
  3. PDM initializes the S7 routing channel, connects through the CPU 410-5H, routes through IM 655-5FF, and opens the online parameterization interface.

Verification

To verify that PDM communication is fully operational:
- In SIMATIC PDM, open the online parameter dialog: verify that the title bar reads Online and the bottom communication status indicates Connected (green).
- Upload parameters from the device (Device -> Upload to PG/PC): verify that all analog calibration ranges, engineering units, and sensor diagnostic logs transfer without communication timeout errors.
- In WinCC Maintenance Station (if active), open the PDM diagnostic view for the device: confirm that the device health state displays healthy green without communication fault flags.

Limitations and Operational Precautions

  • H1 Segment Bus Load: Foundation Fieldbus H1 operates at 31.25 kbps. Uploading massive parameter blocks from multiple field devices simultaneously consumes available bus bandwidth and can introduce temporary jitter into cyclic communication. Perform extensive parameter uploads during stable operating periods.
  • Firmware Compatibility: Ensure the Compact FF Link IM 655-5FF is updated to the latest firmware release (V1.1 or higher) to ensure full compatibility with modern EDD libraries.
  • FF Bus Terminators: Every Foundation Fieldbus H1 segment requires exactly two approved bus terminators (one at each physical end of the cable). Missing or redundant terminators cause signal reflections that disrupt high-frequency acyclic PDM telegrams while slower cyclic signals appear to function.

Engineer FAQ

Does SIMATIC PDM officially support Foundation Fieldbus?

Yes. SIMATIC PDM has fully supported Foundation Fieldbus (FF H1) since PDM V8.x, utilizing the official Foundation Fieldbus Communication Device Library and standard EDD device descriptions.

Why do cyclic values work if the PDM communication fails?

Cyclic data uses deterministic, scheduled time slots negotiated by the Link Master over PROFINET I/O. Acyclic PDM data uses unscheduled token-passing slices; if routing descriptors or EDDs are mismatched, only the acyclic layer fails.

Can I connect PDM directly to the FF H1 segment using a handheld communicator?

Yes. Handheld field communicators (such as Emerson Trex or Siemens field tools) can connect directly to the physical H1 segment wires to configure transmitters independently of the DCS PDM routing.

Where can I check the physical bus health of the FF segment?

The Compact FF Link IM 655-5FF features integrated physical layer diagnostics accessible in HW Config and PDM, reporting signal amplitude, noise levels, and jitter for every connected device.

Technical References

  • Siemens Industry Online Support: SIMATIC PCS 7 Compact FF Link Operating Manual.
  • Siemens Industry Online Support: SIMATIC Process Device Manager (PDM) Manual.
  • SIOS Entry 109742323: PCS 7 Compendium Part A - Configuration Guidelines (Section: Field Device Integration).
  • FieldComm Group: Foundation Fieldbus H1 Communication Profile Specifications.

Related Articles

Related Tags

  • SIMATIC PDM
  • Foundation Fieldbus
  • IM 655-5FF
  • Compact FF Link
  • Diagnostics
  • EDD
  • Industrial Automation
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