Resolving CRC Invalid Error on Siemens SINAMICS CU320-2 PN

Overview

The Siemens SINAMICS CU320-2 PN control unit is the central processor of the SINAMICS S120 modular drive system. It hosts the drive firmware, manages the DRIVE-CLiQ topology, and exposes PROFINET IO to the higher-level controller. A small set of LEDs on the front of the unit (RDY, COM, OPT) reports the operational state to the field engineer.

When a CU320-2 PN is powered up with a corrupted or non-cohesive firmware image, the unit enters a fault state. The internal boot monitor compares the CRC32 checksum stored in the firmware header against a calculated checksum of the firmware blocks on the CompactFlash (CF) card. If the values do not match, the firmware halts, STARTER or Startdrive cannot establish a connection, and the unit announces the fault F01360 "Topology: Error in component" or F01002 "Internal software error" depending on which section of the boot image failed validation. The visible LED symptom is unmistakable: RDY and COM blink red at 0.5 Hz while OPT remains dark.

This article walks through the field procedure to recover a CU320-2 PN that reports a CRC invalid condition, including a CF card re-image, firmware reload, and post-recovery verification. The procedure applies to the PN variant (article number 6SL3040-1MA01-0AA0) and the DP variant (6SL3040-1MA00-0AA0) with firmware V4.4 through V5.4. The older CU320 (non-2) control unit uses a different CF card and is not covered here.

Identifying the Control Unit and Confirming the Fault

Before performing any recovery action, confirm the exact hardware version and firmware state of the unit. The part number is printed on the front label. Each CU320-2 carries a serial number and a nameplate that lists the firmware version that was loaded at the factory.

Read the firmware version that is currently installed using the Accessible nodes search in STARTER, or by reading parameter r0018 (Control unit firmware version) once a connection is established. If the unit is in the CRC invalid state, the firmware will not respond to either method and the only diagnostic is the LED pattern.

LED State Decoding for the CU320-2

The CU320-2 front panel has three status LEDs. The pattern must be read with the unit powered and no STARTER connection active. The table below lists the documented states from the SINAMICS S120 Function Manual.

Root Cause Analysis of the CRC Invalid Condition

The CRC invalid fault has three primary root causes. Field data shows the first one is by far the most common.

1. Interrupted firmware write. The CF card was removed or the CU320-2 lost 24 VDC during a firmware update. The firmware blocks on the card are now in an inconsistent state, and the boot loader rejects the image.
2. CF card file system corruption. A reader/writer that does not fully support the CU320-2 file layout (for example, an unaligned write or a pulled USB mid-write) leaves the FAT file system inconsistent. The boot loader detects the bad cluster and reports CRC invalid even if the firmware image itself is intact.
3. Wrong firmware package on the card. A CF card was prepared with STARTER for a CU320-2 DP, then inserted into a CU320-2 PN (or vice versa). The boot loader checks the variant byte in the firmware header and refuses to start.

The CF card hardware itself is rarely the cause. The SINAMICS S120 CF card (article 6SL3054-0EF00-1BA0) is industrial-grade SLC NAND with a rated endurance of 100,000 program/erase cycles per block. Genuine Siemens cards rarely fail electrically; counterfeit cards sold through gray-market channels fail regularly and should be replaced with a sourced-from-authorized-distributor unit if a hardware fault is suspected.

Pre-Recovery Checklist

Before touching the CF card, perform the following isolation steps. The user-reported symptom in the source thread (CRC invalid persists after the encoder was removed and after restoring a backup folder to the card) indicates a corrupted firmware image, not a peripheral problem. The procedure below confirms this.

1. Remove all DRIVE-CLiQ nodes. Power down the unit and disconnect every DRIVE-CLiQ cable (X100 through X105 on the CU320-2). The unit must boot with the most minimal topology possible.
2. Verify the 24 VDC supply. Measure at terminal X124: pin 2 (+24 V) referenced to pin 4 (GND). Acceptable range is 20.4 V to 28.8 V (Siemens rated). Voltages outside this range cause write errors during normal operation and can corrupt the CF card.
3. Back up the existing CF card image. Before any modification, image the card to a file using a Windows tool such as Win32DiskImager (read-only mode) or the Linux dd command. This gives a recovery point if the wrong firmware is loaded.
4. Document the original firmware version. The label on the card may list a version (for example, "V4.4 SP3"). If not, check the bill of materials or the project's commissioning report.
5. Confirm the PC tools available. Use STARTER V5.4 SP3 (for firmware V4.x and V5.x) or Startdrive in TIA Portal V15.1 or later (for firmware V5.2 SP1 and above). Do not use STARTER V4.x for V5.x firmware; the version mapping in STARTER 4.x is locked to the older firmware generation.

Recovery Procedure: Step-by-Step

The procedure below is the field-proven method to recover a CU320-2 PN from the CRC invalid state without replacing the control unit.

Step 1 - Re-image the CF card

1. Power down the CU320-2 PN and remove the CF card by pressing the eject button on the front of the unit.
2. Insert the card into a CF card reader attached to the commissioning PC.
3. Image the existing card to a backup file: dd if=/dev/sdX of=cu320_backup.img bs=1M status=progress (Linux) or use Win32DiskImager in Read mode (Windows).
4. Run a file system check: chkdsk /f E: (Windows) or fsck.vfat -a /dev/sdX1 (Linux). The user's source thread confirmed that chkdsk may report no errors. This is expected when the corruption is in the firmware blocks, not in the file allocation table.
5. Reformat the card as FAT32 with a 32 KB cluster size. This is the layout the CU320-2 expects.

Step 2 - Load the correct firmware

1. Open STARTER (or Startdrive) and create a new offline project.
2. Use Accessible nodes with the PC connected directly to the CU320-2 PN's X127 service port. The service port has IP 169.254.11.22 by default. Configure the PC service interface to the same subnet (for example, 169.254.11.21).
3. Right-click the CU320-2 in the project tree and select Target device > Firmware update.
4. Select the firmware version that matches the project (for example, V5.2 SP1 for a standard S120 project). The firmware binary is shipped as a .bin file and is downloaded from the Siemens Industry Online Support portal under entry ID 16804190 (SINAMICS S120 firmware releases).
5. Click Activate. The download takes 5 to 12 minutes depending on the CF card and the firmware version. Do not interrupt 24 VDC during this window.

Step 3 - Verify the new image

1. After the download completes, STARTER prompts to restart the control unit. Allow the restart.
2. Watch the RDY LED. The expected sequence is: red steady (boot), red flashing 2 Hz (CRC check), green flashing 0.5 Hz (firmware load), green steady (ready). The full sequence takes 30 to 90 seconds.
3. Re-search Accessible nodes. The CU320-2 PN should appear with the new firmware version visible in the device identification.
4. Read r0018 via the STARTER expert list. The version string must match the firmware just loaded.

Step 4 - Reload the project data

1. Open the project that was previously stored on the CF card (or download from a backup).
2. Use Load to target device to write the parameter set to the control unit.
3. Save the project to the CF card using Copy RAM to ROM. This step is critical; without it, the parameter set is lost on the next power cycle.

Firmware Version Reference

Use the table below to select the correct STARTER version and matching firmware. The cross-reference is the authoritative source from the SINAMICS S120 List Manual.

Verification: Confirming Recovery

A recovered unit must pass the following checks before being returned to production. Each check corresponds to a measurable signal and a documented expected value.

When to Replace the Control Unit

If the procedure above does not bring the CU320-2 to the green steady state, the unit has a hardware fault. The following signals indicate replacement is required.

• All three LEDs remain dark with 24 VDC confirmed at the input terminal. This points to a failed internal power supply.
• The RDY LED shows red steady (not flashing) immediately at power-up, even with all DRIVE-CLiQ nodes disconnected. The internal boot monitor is reporting a non-recoverable fault, typically a failed FRAM or NAND controller.
• The CF card reader on the unit (not the socket) does not register the card on a known-good card. The internal CF interface is damaged.
• The unit passes the firmware load but faults F30802 (Power unit: EPROM data error) or F08501 (PROFIBUS / PROFINET: configuration error) appear immediately. This indicates the MCU on the control unit is failing.

Order the replacement as article 6SL3040-1MA01-0AA0 (PN variant) or 6SL3040-1MA00-0AA0 (DP variant). The replacement ships without a CF card; transfer the original CF card from the failed unit if it is functional, or use a fresh 6SL3054-0EF00-1BA0 card and reload the project from backup.

Troubleshooting Matrix

Use the matrix below to map the LED pattern and STARTER behavior to the correct root cause. This compresses the diagnosis into a single decision table for the field engineer.

Preventive Measures

Once the CU320-2 is recovered, implement the following operational practices to prevent a recurrence of the CRC invalid condition.

1. Use a UPS on the 24 VDC supply. A 24 VDC dip below 20 VDC during a firmware write will corrupt the image. A small DIN-rail UPS (for example, SITOP UPS1600 with a 3.2 Ah battery) gives enough ride-through to complete a write.
2. Lock the CF card mechanism. The CF card sits in a push-push socket on the front of the CU320-2. In high-vibration installations, the card can back out. Use a service-bracket (article 6SL3054-0EF00-1BA0 includes a retaining clip) or apply a service loop to the cable that prevents the card from migrating out of the socket.
3. Document the firmware version in the project. Save the STARTER project with a versioned file name (projectname_V5.2SP3_2024-01-15.zip) and back it up to a network share. A CRC invalid condition is much faster to recover from if the matching firmware and parameter set are at hand.
4. Source CF cards from authorized distributors. Counterfeit cards have a 5 to 10 times higher fail rate in the field. The Siemens article 6SL3054-0EF00-1BA0 is serialized; verify the serial on the support portal before commissioning.
5. Do not interrupt a firmware download. The 5 to 12 minute download window must be uninterrupted. Schedule firmware updates during a planned outage, not during a production break.

Parameters and Diagnostic Addresses

The following parameters are used to diagnose the CU320-2 state once a connection is established. All parameters are read-only while the control unit is in the CRC invalid state, but they are referenced here so the field engineer can confirm the post-recovery state.

FAQ