Resolving SINAMICS S120 CU320-2 Fault 1000 With 4 Motor Modules

1. Problem Statement

A SINAMICS S120 line-up centred on a CU320-2 DP control unit (MLFB 6SL3040-1MA00-0AA0 or 6SL3040-1MA01-0AA0 for newer revisions) is configured with one Basic Line Module (≈100 kW, 167 A, MLFB 6SL3130-1TE22-0AA0 family) and four Single Motor Modules of type 6SL3120-1TE23-0AA4 (30 A, booksize, internal air cooling). When the project contains 3 Single Motor Modules, the drive download and run-up in STARTER/SIMOTION SCOUT completes without errors. As soon as the fourth motor module is enabled and the project is downloaded to the target, the drive system rejects the configuration with:

• Fault F01000 – Internal software error on the CU320-2 (or on the affected Motor Module after topology comparison).
• STARTER message: "Internal software error has occurred."
• Help event suggests: power on/off the complete drive line-up, or upgrade the firmware.

Repeated power cycling of the Basic Line Module, the Control Unit, and all Motor Modules does not clear the fault. The drive remains in topology error / commissioning inhibit state.

2. Why the Fault Appears Only With 4 Motor Modules

The drive system worked with 3 axes and broke when a 4th was added. This is a strong indicator that one of the following internal limits has been reached, and that the 4th axis is the trigger that exposes it:

2.1 CU320-2 Axis and Node Limits

The CU320-2 has a fixed resource budget. Adding a Motor Module consumes:

• One axis resource in the drive object list.
• One DRIVE-CLiQ node address in the physical topology.
• A slice of the parameter set memory on the CF card.
• Additional cyclic PROFIBUS/PROFINET slots if the axis is mapped to a PZD.

Three axes are well under the ceiling, so the limit being crossed at 4 is unlikely to be the axis count itself. The most probable boundaries in a 3 → 4 transition are:

1. CF card capacity or generation mismatch.
2. Firmware compatibility between CU, Basic Line Module, and Single Motor Modules.
3. DRIVE-CLiQ topology order (port assignment or wiring order differs from the offline configuration).
4. Project offline/online version skew (older STARTER project loaded onto a newer firmware CU, or vice versa).

2.2 CF Card and Memory Image

The CU320-2 boots from a CompactFlash card. The card holds the firmware, the parameter image, and any user projects. With each additional Motor Module the parameter set grows because the drive object list and the BICO interconnections are expanded.

Two distinct card generations exist in the field:

3. Root-Cause Map for F01000 with 4 Motor Modules

Use the matrix below to triage. Items 1 – 4 are the most common for the 3 → 4 transition symptom.

4. Inline Topology Diagram

5. Step-by-Step Resolution Procedure

5.1 Pre-requisites

• STARTER (or Startdrive) ≥ V5.x with the correct SINAMICS support package (SSP) installed.
• CF card MLFB and current firmware version noted from the existing card (read with a CF card reader if you have to).
• Functional backup of the current (3-axis) project that is known to work.
• Spare CF card 6SL3054-0ED00-1BA0 recommended for the recovery.

5.2 Procedure

1. Capture the CF card MLFB. Power off, remove the card from the CU320-2, and read the label. Record the MLFB (e.g. 6SL3054-0AA01-1AA0) and the printed firmware version (e.g. V4.8).
2. Capture all firmware versions online. In STARTER, connect to the drive unit, open Drive unit → Version overview. Record the FW version of:
   • CU320-2 control unit
   • Basic Line Module (Type BLM)
   • Each Single Motor Module (Type SLM / SMM)
   All four rows must show the same firmware version. Mixed versions (e.g. CU on 4.8, MM on 4.7) are a common trigger for F01000.
3. Compare against the project's offline firmware. Right-click the drive unit → Properties → Firmware. If the offline FW differs from the online FW, the parameter image cannot be loaded cleanly. The "Internal software error" is the CU rejecting the mismatched image.
4. Check the CF card capacity. With a CF card reader, copy the entire card contents. Look at the OEM / USER folder. If the cumulative parameter sets for 4 motor modules exceed ~ 70% of free space, the next Save RAM to ROM will fail with F01000.
5. Re-load a matched firmware package. Using STARTER → Target system → Load firmware to drive unit, select a unified firmware version that supports 1 LM + 4 MM on a CU320-2. Recommended baseline is the latest released S120 firmware package that lists your MLFBs in the compatibility matrix.
6. Verify DRIVE-CLiQ topology online. In STARTER, open Topology. Confirm that the port order matches the cabinet wiring: CU port 0 → Line Module → MM1 → MM2 → MM3 → MM4. If the on-line topology differs (e.g. MM4 detected on a different port), the CU raises F01302 or F01000.
7. Reload the project. Right-click drive unit → Load to target device → tick Load the parameter set with backup of the actual data. After the download, perform a power off / power on of the complete line-up.
8. Save the project to the CF card. Right-click drive unit → Copy RAM to ROM. The CF card now holds the working image. Verify by removing the card, re-inserting, and observing a clean boot.

6. Commissioning Flow

7. Verification Checklist

8. What If the Fault Persists

If the steps above do not clear F01000 on the 4-axis configuration, the issue is no longer a configuration boundary. The next escalation is:

1. Reduce to 3 MMs in the project, save to CF card, and confirm the line-up boots cleanly. This isolates whether the firmware/CF card environment is healthy.
2. Add MM4 back, re-load, and watch the order of DRIVE-CLiQ LEDs. If a DRIVE-CLiQ LED on a specific port goes red, that port or cable is suspect.
3. Capture a detailed fault buffer (STARTER → Save service data) and the exact CF card MLFB. Open a Siemens support request quoting all of: drive object list, FW version, CF card MLFB, Basic Line Module order code, and the fault timestamp.

9. Related SINAMICS S120 Faults to Cross-Check

10. Practical Field Notes

• Always record the exact CF card MLFB before swapping or upgrading firmware. The MLFB, not the printed FW, drives compatibility.
• CF cards of different generations cannot be hot-swapped. A 512 MB card with old FW will not boot on a system that requires a 4 GB image.
• DRIVE-CLiQ port 0 on the CU320-2 is normally reserved for the line module (or first motor module in some configurations). Re-deriving this assignment after adding MM4 is a frequent cause of topology / F01000 errors.
• Use only Siemens DRIVE-CLiQ cables (6SL3060-4Axx series). Third-party cables with the same RJ50 pinout frequently cause intermittent F01000 and F01302.
• After every firmware change, perform a factory reset via STARTER on the affected components before reloading the project. This avoids residual parameter images that contribute to F01000.

11. Frequently Asked Questions