Resolving CU310-2PN Telegram 105 Isochronous Mode Error

Resolving CU310-2PN Telegram 105 Isochronous Mode Error on SIMOTION D410-2PN

When a SIMOTION D410-2PN controller is paired with a SINAMICS S120 CU310-2 PN drive and the project uses SIEMENS telegram 105, PZD-10/10, the TIA Portal / SCOUT compile often fails with two isochronous-mode diagnostics. This reference documents the precise compiler error text, the underlying cause (DSC + IRT requirement of telegram 105), and the exact topology, sync-domain, and drive-object configuration sequence required to clear the fault on hardware configuration cu003.

1. Problem Details: The Two Compiler Errors

After dragging the SINAMICS S120 CU310-2 PN into the device configuration of a SIMOTION D410-2 PN project, assigning the drive to a TO axis, and selecting SIEMENS telegram 105, PZD-10/10 in the power-module properties, the TIA Portal hardware compile (or SCOUT HWConfig compile) terminates with the following two messages:

Both diagnostics point to the same root constraint: the chosen telegram mandates Dynamic Servo Control (DSC), and DSC in turn mandates PROFINET IRT with high-performance synchronisation plus an isochronous application cycle on the controller.

2. Root Cause: Why Telegram 105 Forces IRT + DSC

Siemens standard telegrams are not interchangeable. Their process-data length and the presence of additional control/status words dictate the bus-class requirements:

Telegram 105 includes the encoder actual value (G1_XACT, 32-bit) and the position deviation XERR words required by DSC. Because the controller uses XERR to pre-compute the next speed setpoint inside the position-control cycle, jitter above 1 µs would destabilise the loop. PROFINET RT class 1 (RT) cannot guarantee that jitter, so Siemens restricts DSC telegrams to IRT high performance (RT class 3) with the IO device flagged as an isochronous synchronous slave.

3. Affected Versions and Compatibility

Refer to the SINAMICS S120 Communication Function Manual (1218) for the canonical telegram-to-RT-class mapping and to the TIA Portal manual collection: Configuring SINAMICS S120 for the drag-and-drop procedure used by SIMATIC S7-1500 projects.

4. Prerequisites

1. Hardware: SIMOTION D410-2 PN (6AU1410-2AA00-0AA0 or higher) with a CU310-2 PN Control Unit (6SL3040-1LA01-0AA0 or higher) on a real PROFINET IRT-capable switch topology. Plain RT switches and wireless segments are not allowed.
2. Engineering tool: SCOUT TIA ≥ V5.4 SP1 (HF1) or TIA Portal ≥ V16 Update 4 with the SINAMICS S120 CU310-2 PN HSP.
3. Firmware on the CU310-2 PN: V4.5 SP3 or V5.x, project compatible with the SCOUT version.
4. Sync cycle budget: A servo cycle of 1 ms or 2 ms on the D410-2 PN. The PROFINET send clock must be 250 µs, 500 µs, or 1 ms. Set Ti (input) and To (output) equal to one PROFINET cycle.
5. Cabling: Direct port-to-port (D410 PN port 1 → CU310 PN port 0) or via a managed IRT switch (e.g. SCALANCE XC-200, XR-300) — never via an RT-only or unmanaged switch.
6. Drive telegram selected on the correct slot: The SIEMENS telegram 105 must be assigned to slot 2 subslot 2 (drive object DO1 = Control Unit / drive), not to the CU module itself. See section 7.

5. Solution Workflow: Step-by-Step

The fix is a three-part change to the offline hardware configuration: port topology, sync-domain rules, and the drive-object slot assignment. After each change, recompile to verify.

5.1 Insert the SINAMICS S120 in the network view

1. Open the project in TIA Portal / SCOUT TIA and switch to the Network view.
2. In the hardware catalog, navigate to Drives > SINAMICS S120 > CU310-2 PN. The supported firmware variant — e.g. V4.5 — must match the target firmware on the physical CU.
3. Drag the drive onto PROFINET IO system 1 of the D410-2 PN.
4. On the drive's PROFINET interface, set the IP address and device name (default cu003 is acceptable, but the name must be unique inside the sync domain).

5.2 Select the correct telegram on the drive object

The most common configuration mistake — and a second, independent cause of the same compile error — is selecting the telegram on the Control Unit slot (slot 0) instead of on the drive (slot 2 subslot 2).

1. Open the device view of the CU310-2 PN.
2. Expand the drive in the slot list. The drive object is located at slot 2, subslot 2. The Control Unit occupies slot 0.
3. Right-click Drive object (DO1) → Properties → Module parameters → Telegram configuration.
4. Set the telegram to SIEMENS telegram 105, PZD-10/10 (or 106/111/116 for two-encoder applications).
5. Confirm that the Control Unit slot (slot 0) still shows the default telegram (typically telegram 391 for CU310-2 PN, which carries only diagnostic / identification data and is not subject to DSC).

5.3 Configure the port topology

The PROFINET topology editor ties each port to a specific peer port, allowing the offline compile to verify that the IRT high-performance path can be synchronised.

1. Right-click the PLC PROFINET interface (the D410-2 PN port 1) and select Topology. The topology editor opens.
2. Add a port interconnection: D410-2 PN port 1 ↔ CU310-2 PN port 0. If an IRT switch sits in between, interconnect all four relevant ports and identify the switch as a managed PROFINET device.
3. Save and close the editor.

5.4 Define the sync domain (Sync-Master / Sync-Slave)

1. Right-click the PLC PROFINET interface and select Domain Management > Sync Domain.
2. Create a sync domain (default name Sync-Domain_1).
3. Set the D410-2 PN to Sync-Master. The role is taken from the Synchronization role drop-down in the interface properties.
4. Move the CU310-2 PN to the same sync domain and set it to Sync-Slave.
5. Confirm the RT class is set to IRT high performance (RT class 3) for both nodes.

5.5 Configure bus cycle times and isochronous mode

1. Open Properties > PROFINET interface > Real time settings of the D410-2 PN.
2. Set the send clock (e.g. 1.000 ms). The send clock becomes the PROFINET IRT cycle.
3. Open Properties > IO cycle of the CU310-2 PN drive slot 2 subslot 2.
4. Tick Operate isochronously and set Ti (input time) and To (output time) equal to the send clock. For 1 ms send clock: Ti = To = 1.000 ms.
5. On the D410-2 PN, open Properties > Synchronous Cycle Interrupts (or Isochronous Mode Tasks in SCOUT TIA) and assign the servo task. The reduction ratio must yield the same 1 ms or 2 ms servo cycle.

5.6 Compile the configuration

1. Right-click the Devices & Networks node and select Compile > Hardware and software (rebuild).
2. Confirm that the slot 2.2 and DSC errors are no longer reported. The expected outcome is a clean compile with the Isochronous mode field populated and the Sync-Slave role visible in the CU310-2 PN properties.

6. Verification Checklist

After the configuration compiles, run the following checks in SCOUT TIA / TIA Portal and on the live system:

1. Offline: In the device view of the CU310-2 PN, slot 2 subslot 2 must show the entry Isochronous mode: yes and RT class: IRT in the module parameters. If either is missing, the topology was not built.
2. Topology view: All ports along the IRT path must display the green check mark for topology configured.
3. Sync domain: In Domain Management, the D410-2 PN must be the only Sync-Master and the CU310-2 PN must be a Sync-Slave.
4. Online (after download): Open Online & Diagnostics > PROFINET diagnostics on the drive. The Sync-Slave status must read synchronised (SYNC_OK) with jitter well below 1 µs.
5. DSC status word: On the drive, parameter r0108.0 shows the firmware configuration bits; bit 0 of r1199 (DSC active) must be 1 after the axis has been enabled.
6. Position controller: Enable the axis and command a small jog. The position controller must remain stable and the following error must be in the single-digit micrometre range. If the loop oscillates at the send-clock frequency, Ti/To or the reduction ratio is wrong.

7. Common Error Matrix

8. Telegram 102 Fallback: When DSC Is Not Available

If the network cannot support IRT high performance — for example because the drive shares a PROFINET segment with HMI panels running RT class 1 — switch the drive to SIEMENS telegram 102, PZD-6/10. Telegram 102 does not contain XERR, so DSC is disabled. The position control loop is then closed in the SIMOTION D410-2 PN, and the CU310-2 PN operates as a torque / speed follower. The same port topology and sync-domain rules can be relaxed; the drive only requires RT class 1 (real-time) on PROFINET.

This is the path of least resistance when:

• The mechanical requirement does not need sub-micrometre following error.
• Existing cabling includes an RT-only switch.
• The PROFINET network is shared with non-IRT devices that cannot be migrated.

9. Parameter Reference

Drive-side parameters that confirm DSC and isochronous-mode state. Adjust as read-only on a live system unless diagnostics demand write access via p0010 = 6 (drive commissioning) mode.

10. Frequently Asked Questions