Resolving Error 33:17075 in STEP 7 V5.5 with CPU 315-2DP

1. Problem Definition

When using SIMATIC STEP 7 V5.5 (Simatic Manager) to perform an "Upload Station to PG" or a "Download to Target Device" operation against a SIMATIC S7-300 CPU 315-2DP, the operation aborts immediately and the software reports the diagnostic return code 33:17075. The PC connects to the PLC through a Siemens PC Adapter (most commonly the USB variant 6ES7972-0CB20-0XA0) and the CPU's MPI or PROFIBUS-DP port. The cable and connector are physically seated, the CPU is in RUN or STOP with the green Power LED on, but the PG/PC cannot establish a compatible online connection.

The error string in this case is not a CPU diagnostic buffer entry (CPU-side SF/BF would be reported through the Module Information dialog); it is a STEP 7 communication layer return code where 33 is the event class for parameter assignment / network parameter mismatch and 17075 is the specific event number that signals a baud rate or bus profile incompatibility between the configured PG/PC interface and the live MPI/PROFIBUS segment. The same event is often paired with messages such as "Online: The configured network parameters are not compatible with the network that is connected."

2. Affected Hardware, Firmware, and Software

The event occurs on the following component combinations:

CPU 315-2DP defaults its MPI interface to 187.5 kbps and its PROFIBUS-DP interface to a configured DP master or DP slave profile. STEP 7 inherits those values from HW Config. If the PG/PC interface is set to a different baud rate (most commonly 1.5 Mbps on a fresh install or 19.2 kbps for legacy MPI) the link fails with 33:17075 because the bus segments cannot auto-negotiate.

3. Root Cause Analysis

Four overlapping root causes account for roughly 95 % of field reports:

1. Baud rate mismatch between STEP 7 and the live MPI/PROFIBUS segment. The PG/PC interface is set to a fixed baud rate that does not match the subnet profile in HW Config. STEP 7 does not perform a baud rate search when the user has selected a fixed profile.
2. Wrong access point / wrong interface assignment. The "Set PG/PC Interface" dialog points at S7ONLINE with the PC Adapter Auto profile, but the project expects PC Adapter (MPI) or PC Adapter (PROFIBUS). The 33:17075 event fires when S7ONLINE opens a handle to a bus profile that the project cannot route to.
3. PC Adapter driver not installed or wrong driver version. The device shows up in Windows Device Manager as "USB Serial Converter" rather than "SIMATIC PC Adapter USB" or "PC Adapter USB V2." The general FTDI/CP210x driver does not implement the S7 communication handshake and silently drops requests.
4. Highest MPI address / bus terminator mismatch. The HW Config MPI subnet defines an MPI address range or "Highest MPI Address" that conflicts with another device on the bus, or the terminating resistor is missing on a long segment, causing the adapter to interpret reflection as garbled frames and return 33:17075.

A fifth, less common cause is a corrupt online cache in the STEP 7 project (the .s7p cache for "Accessible Nodes"). Deleting this cache forces STEP 7 to rebuild the topology table from the live bus.

4. Prerequisites and Required Tools

• STEP 7 V5.5 SPx installed with the matching PC Adapter driver DVD or KB update.
• Siemens PC Adapter USB 6ES7972-0CB20-0XA0, firmware >= V2.0.
• PROFIBUS/MPI cable with 9-pin sub-D connectors (article number 6ES7901-0BF00-0AA0 for the standard 6 m version).
• Administrator rights on the engineering PC (required to install the PC Adapter USB driver and to bind the access point).
• Read access to the offline STEP 7 project (or the ability to start a new empty project and use Accessible Nodes for a clean upload).
• For a physical check: a multimeter to verify 24 V on the CPU front connector pins 1 (24 V) and 20 (M).

5. PC Adapter Driver Installation

Open Windows Device Manager and confirm the adapter enumerates as "SIMATIC PC Adapter USB" or "PC Adapter USB V2." If it shows up as a generic USB serial port, the Siemens driver is not bound:

1. Download the latest PC Adapter USB driver from the Siemens support portal (article ID 109767130 in the Siemens Knowledge Base).
2. Unplug the PC Adapter, run the installer as administrator, and reboot.
3. Plug the adapter into the same USB port that was used during installation. The CP210x-based adapters enumerate on the same port every time; changing the port can re-trigger the generic driver path.
4. Verify that the green POWER LED on the PC Adapter illuminates immediately and the yellow ACTIVE LED flashes when STEP 7 issues a request.

6. Set PG/PC Interface Configuration

The "Set PG/PC Interface" dialog is the control center for resolving 33:17075. Open it from the Windows Control Panel (Start > Control Panel > Set PG/PC Interface) or directly from Simatic Manager: Options > Set PG/PC Interface.

1. In the Access Point of the Application dropdown select S7ONLINE.
2. In the Interface Parameter Assignment Used list choose one of the following, depending on which CPU port you are connecting to:
   • PC Adapter (MPI) — for the CPU 315-2DP X1 port.
   • PC Adapter (PROFIBUS) — for the CPU 315-2DP X2 port (or any DP master/slave on the segment).
   • PC Adapter (AUTO) — only for diagnostic probes; do not leave this selected for the project because it can race with the access point and return 33:17075.
3. Click Properties. In the MPI (or PROFIBUS) tab:
   • Set Transmission Rate to 187.5 kbps for MPI unless your project overrides it.
   • Set Highest MPI/PROFIBUS Address to 31 for the diagnostic search (the default DP address is 2).
   • Set the local Own MPI/PROFIBUS Address of the PG/PC to 0 (PG default; do not use 1, which is the CPU).
4. Click OK, confirm the change with OK in the warning dialog about overwriting the system registry. The setting is now bound to S7ONLINE.

7. HW Config MPI/PROFIBUS Network Parameter Verification

Open the offline project in HW Config, right-click the MPI or PROFIBUS subnet row, and select Object Properties. Cross-check the following against the live bus:

Click Save and Compile (HW Config > Station > Save and Compile). If the bus parameters were modified, save the new values into the CPU with PLC > Download to Target Device, or the mismatch will persist on the live bus even though the offline project is correct.

8. Baudrate Selection Strategy

For the 6ES7972-0CB20-0XA0 PC Adapter, the supported MPI/PROFIBUS transmission rates are:

STEP 7 V5.5 enumerates the supported rates in the PG/PC interface dialog. If a 9.6 kbps option is missing, the project has been saved with a non-default profile or the driver is an old release. Switch the driver in Set PG/PC Interface > Properties > MPI/PROFIBUS from the "PC Adapter (MPI/AUTO)" entry to the explicit PC Adapter (MPI) entry to unlock the full list.

9. Step-by-Step Resolution Procedure

1. Power down the S7-300 station, then power it back up. Confirm the CPU displays RUN or STOP with no SF/BF LED on. Clear any existing diagnostic entries with the mode selector (MRES) only if a download is not in progress.
2. Connect the PC Adapter to the CPU's MPI port (X1). Observe the PC Adapter LEDs:
   • Green Power on, red Error off — adapter is healthy.
   • Yellow Active flashing when the cable is plugged into the CPU — physical layer is up.
3. Open Options > Set PG/PC Interface in Simatic Manager. Set the access point S7ONLINE to PC Adapter (MPI).
4. Open the project. In HW Config, right-click the MPI subnet and confirm the transmission rate matches the value in the PG/PC interface properties (187.5 kbps default).
5. Right-click the CPU and select PLC > Upload to PG. If the upload returns 33:17075 again, use PLC > Accessible Nodes to verify the bus is visible to the PG. A successful Accessible Nodes scan with the CPU listed proves the physical and data-link layers are intact, which localizes the problem to the project routing.
6. Re-bind S7ONLINE to the PC Adapter (PROFIBUS) access point if you are connecting to the X2 PROFIBUS port, then retry.
7. Reboot the engineering PC. The PC Adapter USB driver sometimes holds stale parameters until the host stack is reset.

10. Verification and Commissioning Checks

After completing the procedure, run the following checks to confirm the fault is cleared:

• Accessible Nodes scan. PLC > Accessible Nodes must show the CPU with its MPI/DP address and the upload arrow must succeed.
• Online > Module Information. The diagnostic buffer should not contain any entry timestamped with the last upload attempt referencing 33:17075.
• Cyclic test. Start a small download of a single FC (function) and verify the online/offline comparison (PLC > Compare) shows equal block checksums.
• LED check. The PC Adapter's yellow Active LED should toggle for every request; the red Error LED must remain off.
• PG/PC diagnostic trace. Activate Set PG/PC Interface > Diagnostics tab and start a long trace. Successful frames are logged as "MPI OK" or "DP OK." Any 33:17075 event is logged with the offending baud rate and address, which confirms the parameter mismatch path is closed.

11. Troubleshooting Matrix

12. Extended Diagnostics and Field Tips

For intermittent 33:17075 events that survive the configuration steps above, enable the Online > Online Connection Diagnostics trace and capture the raw telegram exchange. The relevant events are:

• 0xF0 telegram rejection — indicates an MPI address conflict.
• 0x0E token timeout — indicates a bus termination or repeater power issue.
• 0x14 FDL status error — typically caused by a baud rate mismatch in a multi-master segment.

If the project was originally commissioned with a third-party CP card (CP5611, CP5613, CP5711) and you are now using a USB PC Adapter, the S7ONLINE access point may still reference the old CP. Open Set PG/PC Interface, delete the unused entries from the Interface Parameter Assignment Used list, and confirm only the USB PC Adapter entry remains bound to S7ONLINE.

For permanently installed cells, capture the bus profile from a working machine and replicate it in the offline project to avoid drift between machines. The bus profile is stored in the STEP 7 project under System Data > Subnet > Properties.