Configuring CP 343-1 as PROFINET IO in STEP 7 Professional

Problem Overview

During a PROFIBUS-to-PROFINET migration on an S7-300 station, the CP 343-1 communications processor is added to the S7-300 rack in HW Config to act as a second PROFINET interface, but the module's object properties do not expose the PROFINET IO controller operating mode. As a result, no PROFINET subnet can be inserted on the CP, no PROFINET IO devices (such as SINAMICS G120 drives) can be assigned below it, and the project cannot be compiled for a network that is intended to terminate on the CP.

The reported behavior occurs on an S7-300 CPU 315-2 PN/DP (order number 6ES7 315-2AH14-0AB0) with STEP 7 Professional (V5.x and TIA Portal). Two distinct CP 343-1 part numbers are compared in the field, and the choice of variant determines whether the PN IO controller role becomes available in the module properties.

Affected Hardware and Software

CP 343-1 Hardware Family and Role Capability

The CP 343-1 family connects an S7-300 / ET 200M station to a PROFINET network and provides a second PROFINET interface separate from the integrated PN port on PN/DP CPUs. Functionally the CP 343-1 ranges from a Lean variant optimized for simple TCP/IP communication to Advanced variants that support additional protocols, security, and gateway functions. Across the family, the PROFINET IO controller role is a feature of the firmware and of the part number, not a feature unlocked by licensing.

Siemens documents the procedure for operating a CP 343-1 as a PROFINET IO controller in the SIMATIC knowledge base. The application example referenced from the official Siemens support portal covers hardware configuration in STEP 7 Professional, the FB blocks required to move IO data between the CPU and the CP, and the integration of PROFINET IO devices on the CP-owned subnet. The official article is available at CP 343-1 as PROFINET IO controller in STEP 7 Professional (Siemens Support entry ID 109820745).

Why a Variant May Not Show the PN IO Controller Role

When a CP 343-1 part number is dragged into the S7-300 rack, STEP 7 evaluates the module's GSD/GSDML description and the operating mode selector. The first variant tried in the field, 6GK7 343-1EX30-0XE0, did not present the PROFINET IO controller option in the module properties. A second variant, 6GK7 343-1EX21-0XE0, immediately exposed the option and allowed a PROFINET subnet and IO devices to be assigned. The reported behavior is consistent with a configuration problem rather than a hardware defect: the CP must be explicitly placed into PN IO controller mode before the project will allow a PROFINET subnet to be created on the module.

Root Cause: Operating Mode in Module Properties

The PROFINET role of a CP 343-1 is selected in HW Config (STEP 7 V5.x) or in the device view of TIA Portal. The default mode depends on the part number and on the firmware recognized by the engineering tool. If the mode is set to PROFINET IO device, the CP behaves as a subordinate on an external PROFINET network and cannot host its own subnet. To use the CP as an additional IO controller in the station, the operating mode must be set to PROFINET IO controller before any subnet can be inserted.

The field comparison produced three diagnostic observations:

1. On 6GK7 343-1EX30-0XE0, the role selector did not list PROFINET IO controller. The available options were limited to non-controller roles, which is why no PROFINET subnet could be created on the CP.
2. On 6GK7 343-1EX21-0XE0, the role selector listed PROFINET IO controller immediately after insertion, and a PROFINET subnet was created on the CP with no further hardware change required.
3. The role selection, not the slot position, is the gating item. Re-inserting the same CP in a different slot would not change availability of the role.

Prerequisites

• STEP 7 Professional V5.5 SP4 or later, or TIA Portal V13 SP1 or later, installed on the engineering workstation.
• Current Support Package / Hardware Support Package (HSP) that contains the CP 343-1 part number in use.
• S7-300 CPU with at least one free slot in the rack for the CP 343-1 (slot 4 through slot 11 typical for S7-300).
• If integrating SINAMICS G120, the GSDML file for the G120 control unit must be installed in the engineering tool.
• IP plan for the PROFINET subnet. CP 343-1, G120, and any other IO devices need fixed IP addresses and unique PROFINET device names.

Step-by-Step Configuration

Step 1 — Add the CP to the S7-300 Rack

Open the S7-300 station in HW Config (or in the TIA Portal device view). In the hardware catalog, navigate to SIMATIC 300 → Communication → CP 343-1 and select the part number that matches the physical module. Drag it to a free slot. Confirm that STEP 7 logs the part number in the rack view, then double-click the CP to open its object properties.

Step 2 — Set the PROFINET Operating Mode

In the CP properties dialog, open the PROFINET interface → Operating mode page. The role selector lists the modes supported by the recognized firmware. Select PROFINET IO controller. If only PROFINET IO device is listed, the engineering tool is missing the support package for the part number; install the matching Support Package / HSP, restart the tool, and re-open the properties.

Step 3 — Create the PROFINET Subnet on the CP

With the role set to PN IO controller, the New button for a PROFINET subnet becomes available on the PROFINET interface page. Click New to create a PN subnet, assign the subnet name, and confirm. The CP now hosts a PROFINET network that is independent of the integrated PN port on the CPU.

Step 4 — Configure the CP Ethernet Address

On the PROFINET interface → Ethernet addresses page, assign the CP's IP address, subnet mask, and (optionally) router address. The CP and all downstream IO devices must be in the same subnet. Record the IP and PROFINET device name of the CP for later use during commissioning.

Step 5 — Add PROFINET IO Devices

Open the PROFINET subnet. In the hardware catalog, navigate to the appropriate IO device family (for example, PROFINET IO → Drives → SINAMICS → G120). Drag the G120 control unit onto the PROFINET subnet. STEP 7 inserts the G120 as a PROFINET IO device under the CP 343-1, which is now the IO controller for that subnet.

Step 6 — Assign the G120 PROFINET Device Name

Open the G120 object properties, navigate to the PROFINET interface, and assign a unique device name and IP address. The device name must match the configuration stored on the physical G120. Use the Assign PROFINET device name function (PLC → Ethernet → Assign PROFINET device name, or in TIA Portal: Online → Device maintenance) to write the name from the project to the G120.

Step 7 — Map I/O Addresses

For each G120, configure the slot-based I/O mapping. The standard PROFINET slot structure for SINAMICS G120 includes a Telegram (for example, Telegram 1, Telegram 350, or Telegram 352) plus status and control words. Assign input and output addresses that do not overlap with the CPU's integrated PN IO or with the CP-owned subnet's other devices. Record the I-addresses and Q-addresses; the user program will read inputs from the IO device side and write outputs to the IO device side through the standard process image or via explicit load/transfer operations.

Step 8 — Insert the Data Exchange Blocks

The CP 343-1 does not exchange PROFINET IO data with the CPU through the backplane automatically; the user program must call the FB blocks that read the preprocessed input image of the IO devices from the CP and write the output image back. The application example from Siemens Support entry ID 109820745 provides the FBs and the wiring needed for STEP 7 Professional. The reference block reads the preprocessed process inputs of the IO devices from the CP and writes them to the configured I-addresses; a companion block writes the configured Q-addresses back to the CP for transmission to the IO devices. Place both FBs in OB1 (or in a cyclic OB at the same priority) and wire the inputs and outputs to the addresses assigned in Step 7.

Verification

1. Project compilation. Save and compile the HW Config. No errors should be reported on the CP 343-1 or on the G120 IO device. Any error on the CP typically indicates the role is wrong, an HSP is missing, or the slot position is unsupported by the CPU.
2. Station consistency check. In STEP 7 Professional, run Station → Check Consistency. Resolve any cross-reference errors, in particular for cyclic OB1 calls that reference the configured I/Q addresses.
3. PROFINET device-name assignment. After downloading the project, use the Assign PROFINET device name function to write the G120's name. The PROFINET LED on the G120 should stop flashing and remain on solid, indicating that the device name was accepted and the IO device is reachable on the subnet.
4. Online diagnostics. Open the online view of the PROFINET subnet. The CP should report IO controller running, and each G120 should report IO device in data exchange. If the G120 reports Not reachable or Name assignment error, verify the IP address, the device name, and the topology connection.
5. I/O test. In the online view, force a single output bit in the G120's output area. The corresponding LED or status word on the physical drive should change. Read a single input bit back from the G120's input area to confirm that the read path through the CP FB is active.
6. FB call trace. Place a temporary cross-reference or status flag on the FB instance that exchanges data with the CP. Confirm that the FB is being called in OB1 and that its error output (typically RET_VAL or STATUS) is returning zero.

Migration from PROFIBUS to PROFINET

The migration is initiated by the VFD supplier discontinuing PROFIBUS on newer drive generations. On the S7-300 station, the steps are:

1. Replace each PROFIBUS VFD with its PROFINET equivalent, keeping the same drive function (setpoint source, control word mapping, telegram type).
2. Add or repurpose a CP 343-1 as a second PROFINET IO controller for the new drive network, leaving the CPU's integrated PN port for HMI and engineering traffic.
3. For each new PROFINET VFD, install its GSDML, drag the device onto the CP-owned subnet, assign a device name and IP, and remap the I/Q addresses.
4. Adapt the user program. The IO addresses change; the FBs that exchange data with the CP must be re-wired. The control and status word semantics inside the drive follow the PROFIdrive profile, so the higher-level PLC code can remain unchanged once the new addresses are wired.
5. Remove the PROFIBUS GSD files and the old drive DP slaves from HW Config. Recompile and verify.

Troubleshooting Matrix

Operational Notes

• The CPU's integrated PN port and the CP 343-1 each form an independent PROFINET network. They must not be bridged at the IO level. The two networks are joined only through the user program running on the CPU.
• The CP 343-1 firmware version dictates which operating modes are exposed in HW Config. Replacing a CP with a newer or older variant may change the available modes without changing the physical slot or the rack.
• PROFINET device names are case-sensitive and must be unique on the subnet. Use a naming convention that includes the device function (e.g. g120-pump-01) to simplify maintenance.
• For PROFINET IO controllers on the CP, IO device failure behaviour (substitute values, fail-safe behaviour) is configured on the IO device's slot properties, not on the CP.
• CP 343-1 firmware updates are loaded through STEP 7's PLC → Update Firmware function. Update the CP only when the project is in a stable, verified state, and store the previous firmware image for rollback.

Related References in the Siemens Knowledge Base

Siemens Support entry ID 109820745 — CP 343-1 as PROFINET IO controller in STEP 7 Professional — documents the configuration, the data exchange FBs, and the integration with PROFINET IO devices. The entry is available on the Siemens Industry Online Support portal at support.industry.siemens.com/cs/document/109820745. Cross-reference this entry against the firmware and STEP 7 version in use before commissioning.