Resolving 'Topology is Different' Warning on SINAMICS S120 Drives
The "Topology is different" warning appears in SINAMICS S120 commissioning tools (STARTER, Startdrive, or SIMOTION SCOUT) when the DRIVE-CLiQ wiring detected by the Control Unit at power-up does not match the offline commissioning topology stored in the project. On DQ-motor axes (1FK7, 1FT7, 1PH8 with integrated DRIVE-CLiQ interface) the most common root cause is a manual motor MLFB selection that assigns a Sensor Module (SMC/SME/SMI) instead of the motor's internal sensor module, producing a phantom component in the topology. This reference walks through the diagnosis, the corrective configuration in the drive wizard, and the verification steps on SIMOTION D425 and SINUMERIK environments.
1. Topology Architecture Recap
The SINAMICS S120 topology describes the deterministic DRIVE-CLiQ ring/bus that connects the Control Unit (CU320-2, CU310-2, CX32-2, SIMOTION D4x5), Line Modules (Smart/Active/ Basic Line Module), Motor Modules (Single/Double/DTM), Sensor Modules (SMC10/20/30, SME20/25, SME120/125, SMI20/24), Terminal Modules (TM31, TM41, TM15, TM17, TM120, TM150), and any motor or encoder that exposes a DRIVE-CLiQ port. The Control Unit auto-detects the actual topology at every boot and compares it against the target topology embedded in the commissioning data on the CF card. Mismatches raise faults F01350-F01357 or warnings A01350-A01357 in the diagnostic buffer.
| Topology fault / warning | Meaning | Severity |
|---|---|---|
| F01350 | Topology: Component number missing in target topology | Fault, pulse inhibit |
| F01351 | Topology: Target topology invalid | Fault, pulse inhibit |
| F01352 | Topology: Topology comparison detected illegal differences | Fault, pulse inhibit |
| A01357 | Topology: Comparison between actual and commissioning topology produced differences | Warning, no pulse inhibit |
| F01357 | Topology: Line supply / drive type different | Fault, pulse inhibit |
| F01354 | Topology: Different component type detected | Fault, pulse inhibit |
Reference: SINAMICS S120/S150 List Manual (LH1), firmware V5.x — fault and warning list.
2. Why the Warning Appears on DQ-Motor Axes
A DQ (DRIVE-CLiQ) motor integrates the encoder electronics and the Sensor Module on the motor itself. The DRIVE-CLiQ cable is plugged directly into the motor connector, eliminating the SMC/SME in the control cabinet. The motor MLFB (Siemens ordering code) on the rating plate is in the form 1FK7□□-□AF□□-□... with a DRIVE-CLiQ option digit that flags it as a "DQI" motor.
When the axis is commissioned in the drive wizard, the engineer reaches the Motor selection dialog. There are two distinct paths:
- Select motor from catalog (MLFB): the wizard inserts the configured motor type. If the catalog entry binds an external sensor module (e.g. SMC20 for a resolver-based 1FK7), the topology is created with an extra component that does not physically exist when a DQ motor is wired in.
- Select "Motor with DRIVE-CLiQ interface" checkbox: the wizard disables the external Sensor Module and reads encoder parameters directly from the motor's electronic rating plate (EPR / Motor-ID).
Path 1 produces a topology that does not match the actual wiring and triggers the warning. Path 2 is the only correct procedure for DQ motors.
3. Symptoms on SIMOTION D425
On a SIMOTION D425 system with CX32-2 controller extension, the warning manifests in three ways:
- STARTER / SCOUT online diagnostics: red or amber dot on the affected drive object; alarm buffer lists A01357 with detail "Sensor Module on DO2 differs from topology".
-
Device trace: the
TopologyDiffCounterstatus word (r3974) is non-zero and theStateTopology(r3972) reports a difference. - Component manager: the offline component tree in the project navigator shows a Sensor Module under the drive that has no corresponding online component, or vice versa.
On a cold start the drive may additionally raise F01354 ("Component not connected") if the wrong sensor module is configured as a separate component and the DQ motor's internal sensor module is detected in the same DRIVE-CLiQ port — only one component can occupy a port at a time, and the conflict puts the drive into a topology-error state.
SIMOTION D425 reference: SIMOTION D4x5 Manual (PJ), SINAMICS Integrated section.
4. Preconditions for the Fix
- STARTER V5.4 SP1 or higher, or Startdrive V15.1 or higher (TIA Portal), or SIMOTION SCOUT TIA V5.4 SP1 / V5.5.
- SINAMICS firmware V4.8 / V5.1 / V5.2 (D425 platforms use V5.x; check the IBN card sticker for the exact version).
- Configured axis in offline project (i.e. project matches the mechanical assembly).
- DRIVE-CLiQ cable integrity verified — see section 9.
5. Step-by-Step Resolution
5.1 Open the Drive Configuration
- Connect STARTER / SCOUT to the D425 (or CU320-2) online via PROFIBUS, PROFINET, or Ethernet.
- Go online and load the actual topology (Project navigator → Drive Unit → right-click → Topology).
- Open the affected drive object (e.g.
DO2_AxisY) and double-click Configure DDS.
5.2 Reach the Motor Selection Dialog
- The DDS wizard opens with the Configuration overview. Click Next through the control structure, power unit, and BICO screens until you reach the Motor selection page.
- Note the current motor MLFB in the dialog. Click Change to enter the selection list.
5.3 Select the DRIVE-CLiQ Motor Path
- Tick the checkbox "Motor with DRIVE-CLiQ interface" at the top of the dialog. This is the critical step.
- The MLFB catalog list is greyed out for the type field, but the motor code field remains editable if you want to enter the DQ motor's order number directly.
- Confirm the motor code (e.g.
1FK7060-2AF71-1AB1) and click OK.
5.4 Validate the Sensor Module Node
- After the wizard closes, look at the navigator under the drive object. The Sensor Module subnode should now show the motor-internal sensor module (e.g.
Sensor Module Integrated (DQ motor)) and the External SMC/SME that was previously inserted should be gone. - If the wrong Sensor Module is still present, right-click the drive object → Delete the sensor module subnode, then run Configure DDS again with the DRIVE-CLiQ motor checkbox set.
5.5 Compile, Download, and Save
- Project → Compile and check (Ctrl+F7). The compiler must finish with status Warnings: 0 for the affected drive; topology warnings are surfaced here too.
- Go online, right-click the drive unit → Download to target device → RAM and ROM (with copy RAM to ROM). The DQ motor's electronic rating plate is read and the encoder parameters are written into p0340/p0431 automatically.
- Save the project to the CF card: Target system → Copy RAM to ROM, then back up the project file on the engineering PC.
6. Verification
- Power cycle the drive (ON/OFF of the 24 V Control Unit supply, not just the line). The "Topology is different" warning must not reappear in r3972 / r3974.
- Open Diagnostics → Drive unit diagnostics → Topology comparison. The actual and target topologies should match component for component.
- Read the encoder status word r0480 — bits 0 and 1 indicate the encoder is initialised and ready.
- Run a small setpoint step in the commissioning test panel (e.g. n_set = 50 rpm for 1 second). The motor should accelerate cleanly with the correct commutation angle. A reversed commutation is unrelated to topology, but a stalled axis here usually means the encoder is the wrong type — re-check section 5.3.
Reference: SINAMICS S120 Commissioning Manual (GH1), STARTER section.
7. Parameter Reference
| Parameter | Meaning | Typical value for DQ motor fix |
|---|---|---|
| p0099 | Device commissioning parameter filter | 0 (no filter) or 1 (factory setting restore) |
| p0100 | IEC/NEMA standard | 0 = IEC, 1 = NEMA |
| p0300 | Motor type code | MLFB code (e.g. 102 for 1FK7060) |
| p0301 | Motor code (motor with DRIVE-CLiQ) | MLFB or motor ID from rating plate |
| p0340 | Automatic calculation of motor/control parameters | 1 = complete calculation after p0300/p0301 change |
| p0431 | Encoder module number | 0 = automatic (read from DRIVE-CLiQ) |
| r3972 | Topology state diagnostic word | Should read 0 after a clean boot |
| r3974 | Topology difference counter | Should be 0; non-zero → residual mismatch |
Source: SINAMICS S120 List Manual, parameter list, section "Encoder / Sensor Module".
8. Troubleshooting Matrix
| Symptom after fix attempt | Likely root cause | Next action |
|---|---|---|
| Warning persists, identical text | Project not reloaded to ROM, or CF card contains old topology | Copy RAM to ROM, then power cycle the Control Unit. Verify CF card write (LED activity on CU) |
| Warning replaced by F01354 | Sensor Module subnode not deleted before recompile | Delete SMC/SME node, re-run DDS wizard with DQ checkbox |
| Encoder reports "unknown type" (F31118) | Motor ID was not read (p0431 forced to a wrong value) | Set p0431 = 0, then p0340 = 1, then Copy RAM to ROM |
| CX32-2 extension not recognized | CX32-2 firmware mismatch with D425 firmware | Check firmware compatibility matrix, run Tools → Update firmware on CX32-2 |
| Commutation error on first motion | Encoder is the correct type, but p0425 / p0437 polarity | Swap p0410 bit 0 or p0437 if angle is 180° off; not a topology issue |
| Topology diff counter r3974 > 0 but no fault | Additional module present (e.g. TM31 on a port that was configured empty) | Add the module to the project OR remove the module from the wiring |
9. DRIVE-CLiQ Wiring and Diagnostic Checks
Before changing the project, rule out a cable or port issue. The Control Unit provides per-port LEDs:
| LED state | Meaning |
|---|---|
| Off | No module connected or 24 V missing on the partner |
| Green flashing 2 Hz | Module communication active, cyclic data exchange |
| Green flashing 0.5 Hz | Module detected, identification in progress |
| Red solid | Fatal communication error, replace cable/module |
| Red flashing 2 Hz | Cyclic communication error, check EMC and shielding |
DRIVE-CLiQ cable rules (per SINAMICS S120 Commissioning Manual):
- Maximum cable length 100 m between two nodes (fiber-optic 50 µm: up to 300 m).
- Never run DRIVE-CLiQ parallel to motor power cables closer than the cable tray separation defined in the EMC manual.
- Use only Siemens DRIVE-CLiQ cables — color-coded by port speed: grey for fixed-port CU, green for port 0/1 of a D4x5/CX32-2, red for high-speed ports.
10. Edge Cases and Field-Proven Caveats
- 1PH8 main spindle motors: the motor has both a DRIVE-CLiQ interface and a separate SSI encoder on the same axis. You can use the SSI only as a backup; do not enable both — only one sensor module is allowed at the DRIVE-CLiQ port.
- Second encoder on a DQ motor: parameters p0421/p0422 for a second encoder must reference the next free Sensor Module, not the motor's internal one. Mixing the two produces a topology warning plus an F31118.
- Starter < V4.4 / SCOUT < V4.4: the "Motor with DRIVE-CLiQ interface" checkbox is not present. Upgrade STARTER/SCOUT or configure the motor MLFB as an SMI (Sensor Module Integrated) and manually set p0431 to the motor-internal value.
- Drive object number conflicts on D425 with CX32-2: the CX32-2 expands the available DO count; the DQ motor port must land on a DO that exists in the project (max 6 for D425, max 12 for D435/D445, max 16 for D455). Otherwise, the topology reports F01350.
- Hot-plugged components: SINAMICS supports the p9910 = 1 function to re-detect topology on hot-plug, but it does not clear a pre-existing wrong sensor module assignment; you must still go through section 5.
11. Commissioning Checklist
- Confirm Motor MLFB on the rating plate matches the configured MLFB digit by digit.
- Confirm DRIVE-CLiQ port LED on the Control Unit is green flashing 2 Hz when wired.
- In the wizard, the Motor with DRIVE-CLiQ interface checkbox is set before accepting the motor code.
- Sensor Module subnode shows "integrated", no SMC/SME branch.
- Compile clean, download to RAM and ROM, power cycle.
- r3972 = 0, r3974 = 0, alarm buffer clean.
- Test motion in commissioning mode with limited setpoint (≤ 5 % of n_max).
- Back up the project to the engineering PC and to the SINAMICS CF card.
12. Frequently Asked Questions
What does the SINAMICS S120 "topology is different" warning actually mean?
It means the Control Unit detected DRIVE-CLiQ components at power-up that do not match the commissioning topology stored on the CF card. Check the diagnostic buffer for the related fault or warning (typically A01357 or F01357) and the actual versus target topology view in STARTER/SCOUT. Reference: SINAMICS S120 List Manual.
Why does the topology still show an external Sensor Module after I select a DQ motor MLFB?
The catalog path in the motor selection dialog can insert an external SMC/SME in addition to the motor's internal sensor module. You must enable the "Motor with DRIVE-CLiQ interface" checkbox before accepting the motor code, and delete any pre-existing Sensor Module subnode from the navigator.
My SIMOTION D425 does not see the CX32-2 extension; is this the same problem?
Often yes, but the root cause is a firmware mismatch between the D425 and CX32-2. Verify both firmware versions are listed in the SIMOTION D4x5 release notes and update the CX32-2 to the matching version. The topology will not converge if the CX32-2 cannot complete identification.
Can I keep the external Sensor Module SMC20 in the project for a DQ motor?
No. The DRIVE-CLiQ port accepts only one node. The motor's internal sensor module occupies the port, so the SMC20 must be removed. If you need a second channel, use the next available free DRIVE-CLiQ port on the Control Unit and configure it as a separate encoder (p0421/p0422).
After the fix, r3974 is still 1 even though there is no alarm — what is missing?
Topological difference counter r3974 is sticky; it does not auto-reset on every boot. Use Diagnostics → Drive unit → Topology → Reset, or power cycle the Control Unit with the CF card removed and reinserted after the LED goes dark, then re-evaluate. If the count remains non-zero, run Topology → Adjust offline in STARTER to sync the project to the detected actual topology.