Replacing Masterdrive with SINAMICS CU310 Resolving GSD ID

Problem Overview: One-to-One Drive Swap on PROFIBUS DP

A common service/upgrade scenario involves replacing an obsolete Siemens SIMOVERT MASTERDRIVES (6SE70 series) with a newer SINAMICS S120 control unit CU310 DP (6SL3040-0LA00-0AA0 / 6SL3040-0LA01-0AA0) without modifying the PLC project. The field expectation is that the CU310 will accept the telegrams generated for the old Masterdrive. In practice the CU310 rejects parameterization and refuses to enter cyclic data exchange, producing "Slave not found" or "Prm fault" diagnostics on the DP master.

The error is not a wiring fault, not a baud-rate mismatch, and not a missing termination. It is a fundamental consequence of how PROFIBUS DP validates a slave before allowing cyclic communication. Understanding the PNO Ident_Number (Device Identifier) embedded in every GSD file is the key to diagnosing and resolving this problem.

Root Cause: GSD Device Identifier Mismatch

Every PROFIBUS DP slave description is contained in a GSD file (General Station Description). The GSD defines the device's:

• Manufacturer name and product family
• Baud-rate support and bus timing
• I/O slot configuration, modules, and channel counts
• Diagnostic and alarm capabilities
• Ident_Number – a 16-bit value assigned by the PROFIBUS Nutzerorganisation (PNO) and registered uniquely to a specific device model/firmware

When the DP master brings a slave into cyclic operation it executes the standard PROFIBUS DP startup sequence:

1. Check_Cfg – compares configured modules against what the slave reports.
2. Set_Prm – sends parameterization data that includes the expected Ident_Number from the GSD selected in the PLC hardware catalog.
3. The slave compares the received Ident_Number against its own internally stored value (loaded from its own firmware/GSD combination).
4. If Ident_Number matches → the slave returns PRM_CMPLT = 1 and enters DATA_EXCHANGE.
5. If Ident_Number does not match → the slave returns PRM_CMPLT = 0, raises Prm fault in the diagnostic telegram, and remains in WAIT_PRM.

Masterdrive MC/VC and SINAMICS CU310 each have their own registered Ident_Number. The GSD files are not interchangeable because the drive firmware on the CU310 will only acknowledge parameterization telegrams carrying the Ident_Number that matches its own type. A CU310 receiving a Masterdrive Ident_Number from the master will treat it as a configuration error and stay offline.

How PROFIBUS DP Identifies a Slave

The identification flow follows IEC 61158 / IEC 61784 and is part of the DP-V0 state machine. The relevant states are:

• Power_ON / WAIT_PRM – slave waits for parameterization.
• WAIT_CFG – slave waits for Check_Cfg.
• DATA_EXCHANGE – cyclic I/O is active.
• DX-Offline / DX-Failure – slave has dropped out due to a watchdog, configuration mismatch, or Prm fault.

The Prm telegram includes a structured parameter block where bytes 8–9 carry the Ident_Number the master considers valid for this station address. Byte 7 includes the PRM_CMPLT flag the slave sets once it has accepted and stored its parameters. The diagnostic telegram returns the standardized Diag_Data block; relevant bits include:

• Bit 0 – Station_Non_Existent
• Bit 1 – Station_Not_Ready
• Bit 2 – Prm_Fault (the bit set on Ident_Number mismatch)
• Bit 3 – Cfg_Fault
• Bit 4 – Not_Supported

On a CU310 with PROFIBUS DP, a Prm fault typically lights the SF (red) LED solid and the BF (bus fault, red) LED blinks at 0.5 Hz, indicating that parameter assignment did not complete.

Why Parameter Changes Cannot Bypass the Check

Two common workarounds are proposed in field discussions but neither works:

1. "Set the CU310's Ident_Number to the Masterdrive value." The Ident_Number is not a writable drive parameter. It is hard-coded into the PROFIBUS ASIC firmware (e.g., SPC3 / DPC31 / netX) used by the CU310 and matches the GSD shipped with the firmware version. Editing it requires re-imaging the fieldbus chip firmware, which is not a field-revision-supported operation.
2. "Use a PROFIBUS signal converter or repeater to translate telegrams." PROFIBUS repeaters regenerate physical signals but do not change the logical content of parameterization telegrams. A protocol gateway that translates PROFIBUS to PROFINET or to another bus still needs a correctly matched GSD on each side. The gateway cannot teach the CU310 a different Ident_Number.

The only supported path is to reconfigure the DP master.

Solution Path: PLC Project Reconfiguration

If the engineering software for the PLC cannot be opened or modified, the field options are extremely limited. In practice the following three resolutions are documented:

1. Reconfigure the PLC project with the CU310 GSD and re-download the hardware configuration. This is the supported and recommended path.
2. Replace the PLC as well, replacing Masterdrive and the original PLC with a current SIMATIC S7-1500 / ET 200SP controller and the SINAMICS CU310.
3. Use a PROFIBUS DP slave that uses the original Masterdrive GSD – i.e., keep the existing drive stock and replace the CU310 only as a last resort.

Reconfiguration Procedure in TIA Portal V20 (SIMATIC S7-1500 / ET 200SP)

The current Siemens engineering tool for SIMATIC S7-1500 and SINAMICS is TIA Portal V20. The procedure to swap a Masterdrive GSD for a SINAMICS CU310 GSD is:

1. Open the TIA Portal project. Verify the DP master system and the slot currently occupied by the Masterdrive DP slave.
2. Confirm the CU310 DP variant (6SL3040-0LA01-0AA0 or successor) and the matching SINAMICS firmware version installed on the drive. Obtain the matching GSD from the Siemens Industry Online Support portal under "SINAMICS S120 CU310 DP GSD". Typical filenames follow the convention si0xxxxx.gsd or GSDML-Vx.x-Siemens-SINAMICS_S120-... for PROFINET variants.
3. Install the GSD via Options > Manage general station description files (GSD). For PROFIBUS, this places the new GSD into the hardware catalog under Other field devices > PROFIBUS DP > Drives > Siemens AG > SINAMICS.
4. Delete the existing Masterdrive DP slave from the DP master system. Drag the SINAMICS CU310 DP slave from the catalog to the same PROFIBUS address. Match the same station address.
5. Configure the slot mapping. SINAMICS CU310 default slot assignment is typically:
   • Slot 0 – PZD-1/1 (control word + speed setpoint)
   • Slot 1 – PZD-2/2 (additional setpoints)
   • Slot 2 – PZD-3/3 (status word + actual speed)
6. Update the I/O symbols, telegram selection, and any PPO type used by the application. SINAMICS supports standard telegrams 1, 2, 3, 4, 5, 6, 9, 20, 110, 111.
7. Compile and download the hardware configuration to the S7-1500 CPU.
8. Reference the SINAMICS configuration tool (STARTER or Startdrive) to align the drive's free-function blocks and BICO wiring with the new telegram structure. Configure GSD drives for PROFIBUS DP via the TIA Portal documentation describes the exact dialog sequence used to insert GSD-based DP slaves into a TIA project.

Reconfiguration Procedure in STEP 7 V5.x (SIMATIC S7-300 / S7-400)

For installations using older controllers, STEP 7 V5.5 or V5.7 is the matching engineering tool:

1. Open the STEP 7 project and select the HW Config editor.
2. Insert the SINAMICS CU310 GSD using Options > Install GSD File. After installation it appears under PROFIBUS DP > Additional Field Devices > Drives > SINAMICS.
3. Delete the Masterdrive DP slave and drag the CU310 DP slave to the same PROFIBUS address. Keep the address identical so the application program does not need address rewrites.
4. Map the I/Os. The control/status words are on the same logical addresses if the same standard telegram (e.g., Telegram 1: PZD-2/2) is selected. Adjust only if the original application used a PPO type not supported on CU310.
5. Compile and download the hardware configuration to the CPU. Use online > Accessible Nodes to verify the CU310 is now in DATA_EXCHANGE.
6. Re-align the drive-side parameters using STARTER. Pay particular attention to:
   • p0922 – PROFIdrive PZD telegram selection
   • p2051 – control word source
   • p2050 – status word destination
   • p2030 – fieldbus interface selection (PROFIBUS DP = 2 on CU310 DP)

Alternative 1: Migration to PROFINET with CU310 PN

If a complete bus migration is feasible, replacing both the PLC and the bus medium is the cleanest path. The SINAMICS CU310 PN variant (6SL3040-0LA00-0AA1 / 6SL3040-0LA02-0AA0) supports PROFINET IO with RT and IRT. Advantages:

• Eliminates PROFIBUS DP V0 legacy constraints.
• Allows GSDML-based device description, which is easier to maintain and supports shared device, IRT, and media redundancy.
• Combined with an S7-1500 controller the entire system can be engineered in a single TIA Portal V20 project.

PROFINET migration requires a PLC capable of PROFINET IO, the matching GSDML for the CU310 PN, and either a complete controller replacement or an upgrade that adds a PROFINET interface. Existing PROFIBUS segments can be retained by adding an IE/PB Link (6GK1411-5AB10) only if the drives themselves remain Masterdrive.

Alternative 2: Communication Gateways

A PROFIBUS-to-other-bus gateway (e.g., to Modbus TCP, EtherNet/IP, or DeviceNet) can be used to read a few words from the drive, but it does not solve the underlying problem that the drive's GSD must match the gateway's expected PROFIBUS slave description. A gateway will:

• Allow integration into a different control system using a different protocol.
• Still need the SINAMICS CU310 GSD installed as a DP slave on the gateway's PROFIBUS side.
• Add latency (typically 1–2 bus cycle times).

Recommended only when the higher-level control system cannot host a PROFIBUS master and the application can tolerate increased cycle time.

Alternative 3: Unsupported Custom-GSD Spoofing (Not Recommended)

It is technically possible to copy a Masterdrive GSD and modify the Ident_Number field to match the CU310. This approach is occasionally proposed in field discussions but is not supported by Siemens and violates the PROFIBUS conformance requirements of PNO. The risks include:

• Loss of PROFIBUS certification for the bus segment.
• Module mismatch as soon as the application program expects SINAMICS-standard telegram structure.
• No support obligation from Siemens if the drive or PLC fails because of a spoofed GSD.
• Subsequent firmware updates on the CU310 may change the device behavior and invalidate the spoof.

Do not use this approach for safety-relevant or long-term production installations.

Diagnostic Parameters and LED States on CU310 DP

Useful drive-side parameters for confirming the Ident_Number mismatch during commissioning:

On the CU310 DP front panel, the BF LED pattern is the first diagnostic to inspect:

Commissioning and Verification Checklist

1. Verify physical wiring: shielded twisted pair, terminators ON at both ends, PROFIBUS connector with switchable termination (e.g., 6GK1500-0FC10) installed correctly.
2. Set the CU310 DP rotary address switch to the same PROFIBUS address the master uses (1–125).
3. Confirm the GSD installed in the master matches the CU310 firmware version (e.g., SINAMICS S120 V5.x firmware requires the V5.x GSD).
4. Compile, download the HW Config, and go online with the PLC. Read the slave diagnostics – Diag_Data bit 2 (Prm_Fault) must be clear.
5. In STARTER / Startdrive, go online with the CU310. Check r2047 = 2 (DATA_EXCHANGE) and r2054 = 0.
6. Force a small speed setpoint from the PLC (e.g., STW1 = 0x047E then 0x047F) and verify r2050[0] echoes the value and r0063 shows the actual speed.
7. Document the Ident_Number of the installed CU310 GSD. Save the project and the GSD file as part of the asset record for future service.

Frequently Asked Questions