SIMOTION CU320-2 Copy RAM to ROM Fails: Firmware Fix

Problem Description

On a SIMOTION D455 line that includes several SINAMICS S120 CU320-2 PN control units, the operation Target system → Copy RAM to ROM (or its equivalent in SIMOTION Scout) terminates abnormally. After the user has just successfully downloaded a topology change with Download to target device, the Copy RAM to ROM command appears to start normally. The progress bar advances for a few seconds, then the online connection to the affected CU drops to OFFLINE and the operation aborts before completion. The same behavior is observed regardless of whether the SIMOTION PLC is in RUN or STOP. The issue reproduces on most CU320-2 nodes of the line; a small number of CUs and the SINAMICS Integrated on the D455 may complete the copy successfully, but the majority cannot.

This symptom is a known SINAMICS firmware defect on the CU320-2 control unit. It is not caused by SIMOTION Scout, SIMOTION Starter, or the SIMOTION runtime itself. The root cause is the SINAMICS firmware version on the CU320-2, and the definitive remedy is to upgrade the CU320-2 firmware to at least V4.6 (V4.7 recommended) and align the SIMOTION runtime to the matching bundle.

Symptoms and Reproduction Sequence

1. The engineering station establishes an online connection to one CU320-2 of the line over PROFINET (CU320-2 PN variant).
2. The user performs a topology comparison change inside the SIMOTION Scout project and triggers Download to target device. The download completes successfully; the running SIMOTION application on the D455 accepts the new topology without complaint.
3. The user triggers Target system → Copy RAM to ROM on the same CU. The progress bar advances, then within a few seconds the online connection to the CU drops and Scout displays an OFFLINE state for that device.
4. Reconnecting to the CU is possible without a power cycle, but a second attempt to Copy RAM to ROM exhibits the identical failure. The data on the non-volatile media of the CU is therefore never updated; only the volatile RAM image reflects the new topology.
5. The same sequence fails on most CU320-2 nodes in the line. On a small number of CUs (and on the SINAMICS Integrated inside the D455) the operation completes normally, which is consistent with a device-specific firmware-state difference rather than a project-level defect.

Affected Hardware and Software Versions

The exact minimum fix level was confirmed by Siemens support as SINAMICS V4.6 on the affected CU320-2. Because Siemens ships the SINAMICS and SIMOTION firmware as a coordinated bundle, raising the SINAMICS FW on the CU usually forces a SIMOTION runtime upgrade as well. In practice, the upgrade path is therefore: SIMOTION V4.3 + SINAMICS V4.5 → SIMOTION V4.4 + SINAMICS V4.7.

Root Cause: SINAMICS Firmware Defect in V4.5 on CU320-2

The Copy RAM to ROM service writes the volatile parameter image of the CU320-2 onto its non-volatile media (CF card on the CU, or, for integrated configurations, the SIMOTION CF). On CU320-2 with SINAMICS firmware versions below V4.6, this write path is known to terminate the runtime communication context mid-operation. The CU drops its PROFINET/PROFIBUS communication channels to the engineering station, which Scout reports as a transition to OFFLINE. The CU does not crash and does not require a power cycle, but the non-volatile write is interrupted and the parameter image is not committed.

Because the symptom appears only on some nodes of a line and not on others, the failure is not a deterministic crash of the write path itself; it is a probabilistic state-machine or buffer-management bug that is more likely to trigger when the parameter image is large (full topology change + axis data) and when the CF card is being written while the CU is also serving online traffic.

Siemens support has confirmed that the firmware on the CU320-2 (not the SIMOTION runtime, not Scout, not STARTER) is the responsible component. Once all CU320-2 nodes are on V4.6 or V4.7, the Copy RAM to ROM operation completes reliably on every node.

Resolution Overview

Perform a coordinated firmware upgrade of the SIMOTION/SINAMICS bundle:

1. Upgrade SIMOTION Scout on the engineering station to V4.4.
2. Update the SIMOTION CF card of the D455 with the matching SIMOTION V4.4 firmware bundle.
3. Update the CF card of each CU320-2 with the SINAMICS V4.7 firmware image (and matching STARTER commissioning tool).
4. Reopen the project in Scout V4.4, right-click each SINAMICS device and choose Target device → Upgrade device version so the offline project matches the on-device firmware.
5. Download the upgraded project to the line and verify that Copy RAM to ROM now completes on every CU320-2.

SIMOTION / SINAMICS Firmware Compatibility Matrix

The SINAMICS firmware image that lives on the SIMOTION CF card (driving the SINAMICS Integrated inside the D4x5) is part of the SIMOTION bundle and cannot be updated independently of the SIMOTION runtime. The CF card in the standalone CU320-2 is a separate, device-specific card and must be updated on its own.

Hardware Setup Considerations

The D455-2 DP/PN and D455-1 DP/PN variants integrate a SINAMICS S120 control section (SINAMICS Integrated) plus a SIMOTION CPU on a single CF card. A line built around a D455 typically also drives one or more standalone CU320-2 PN units over PROFINET. The two card populations must not be confused:

• SIMOTION CF card — Sits in the D4x5 module. Carries the SIMOTION runtime, the SIMOTION project, the SINAMICS Integrated FW image, and the licensing keys (KEYS folder/file). Re-flashing this card is a SIMOTION firmware update and uses the SIMOTION upgrade bundle.
• CU320-2 CF card — Sits in each standalone CU320-2. Carries the SINAMICS firmware image, the SINAMICS parameter image, and the licensing keys for that CU. Re-flashing this card is a SINAMICS firmware update and uses the SINAMICS upgrade package.

The two CFs are physically identical (CompactFlash) but the images are not interchangeable. Putting a SIMOTION CF into a CU320-2, or a CU320-2 image into the D4x5, prevents the device from booting and is a common field mistake during mixed maintenance windows.

Step-by-Step Firmware Upgrade Procedure

1. Identify the current bundle. In Scout, open Target system → Device diagnostics → Version on the D455 and on each CU320-2. Record the SIMOTION version, the SINAMICS version on the Integrated, and the SINAMICS version on each CU320-2. Anything on SINAMICS < V4.6 is suspect.
2. Download the matching upgrade bundle from Siemens Industry Online Support (entry list for SIMOTION D4x5 and for SINAMICS S120 CU320-2). For the recommended target, download the SIMOTION V4.4 HF bundle and the matching SINAMICS V4.7 package.
3. Upgrade the engineering station by installing SIMOTION Scout V4.4 (and the matching STARTER). Confirm the version with Help → About. Mixing a V4.4 project with a V4.3 Scout is not supported.
4. Update the SIMOTION CF card of the D455:
     a. Power down the D455 and remove the SIMOTION CF card.
     b. Insert the CF into a CF card reader on the engineering PC.
     c. Back up the existing KEYS folder/file from the card. License keys are not contained in the upgrade bundle and must be preserved.
     d. Delete all other content on the CF card.
     e. Extract the SIMOTION V4.4 bundle onto the CF card.
     f. Reinsert the CF card into the D455 and power up. The SIMOTION runtime will detect the new image and unpack the SINAMICS Integrated firmware automatically.
5. Update each CU320-2 CF card with the same procedure: remove, preserve KEYS, wipe, extract SINAMICS V4.7 image, reinsert, power up. Update all CUs in the same maintenance window to keep the line on a homogeneous firmware level.
6. Align the offline Scout project with the new on-device firmware (see next section).
7. Download the upgraded project to the D455 and to each CU320-2, then test the Copy RAM to ROM operation on every node.

Updating the Scout Project Offline (Device Version Upgrade)

A Scout project created against SINAMICS V4.5 cannot establish an online connection to a CU320-2 that has been flashed with SINAMICS V4.7. The version mismatch is enforced at the device-communication layer. The remedy is to upgrade the offline representation of every SINAMICS device in the project:

1. Open the project in Scout V4.4.
2. Right-click the SINAMICS device in the project tree.
3. Choose Target device → Upgrade device version.
4. Select the target version V4.7 from the dialog and confirm.
5. Repeat for the SINAMICS Integrated of the D455 and for every standalone CU320-2.
6. Recompile the project, save, and download to the target system.

After the upgrade, the device description in the project matches the on-device firmware, and Download to target device plus Copy RAM to ROM complete without the connection drop.

Verification

After the upgrade, perform the following checks before returning the line to production:

• Connectivity check. From Scout, go online to every CU320-2 and to the D455. Confirm the device version reported under Target system → Device diagnostics → Version is now V4.7 on the CUs and the corresponding SIMOTION V4.4 release on the D455.
• Copy RAM to ROM test. On every CU320-2, perform a parameter change (e.g., a non-critical p-parameter) and then execute Copy RAM to ROM. The progress bar must complete to 100% and the online connection must remain stable throughout.
• Power-cycle persistence check. Power-cycle each CU320-2 and verify that the change is still active (i.e., the parameter is read back from non-volatile storage, not RAM).
• Topology check. Re-run the topology comparison in Scout; it must report a match (no topology diff).
• Safety acceptance. If Safety Integrated is in use, re-run the safety acceptance test on every PROFIsafe slot that touches a CU320-2.

Edge Cases and Field Cautions

Mixed firmware lines. A line that still has one or two CU320-2 on V4.5 will continue to show the failure on those nodes only. Audit every CU on the network; the version can be read from Scout or from the CU's web server.

Sinamics Integrated cannot be updated independently. The SINAMICS Integrated inside the D4x5 is tied to the SIMOTION bundle. There is no standalone SINAMICS upgrade for it. The only way to raise its FW version is to update the SIMOTION CF card with a newer SIMOTION bundle.

STARTER version dependency. The SINAMICS V4.7 package ships a specific STARTER version. Using an older STARTER (for example, the one bundled with Scout V4.3) against a V4.7 CU can mask parameters and lead to confusing diagnostic messages even though the connection is established.

License key preservation. The KEYS folder/file on each CF card is the only path to keep the runtime licenses after re-flashing. Never wipe the CF without first copying the KEYS to the engineering PC and pasting it back after the extraction. License files cannot be re-generated from the project.

Reconnection after the failure. After the Copy RAM to ROM failure, the affected CU goes OFFLINE in Scout but remains reachable on PROFINET. Going online again succeeds without a power cycle. If a power cycle is performed, the CU320-2 will boot from the still-old CF image (the failed write did not commit), so the symptom returns on the next attempt.

Drive section release. Removing a CF card removes the parameter image of the CU320-2. After re-flashing and reinserting, the CU will boot in a parameter-default state and the drives will not be released until the offline project is downloaded and the commissioning parameters (motor data, encoder data, closed-loop settings) are pushed to the CU. Plan for a partial recommissioning window, not a hot-swap.

Watchdog / timeout during write. If the CF card is slow or nearly full, the Copy RAM to ROM write can take several minutes. Do not interpret a long progress bar as a hang; on V4.6 / V4.7 the write will complete.

Quick Diagnostic Matrix

Frequently Asked Questions