S7-300 Ethernet Setup: PG/PC Interface Configuration in STEP 7

Overview: S7-300 Ethernet Communication Path

The SIMATIC S7-300 family uses the integrated PROFINET interface of the CPU (e.g., CPU 315-2 PN/DP, CPU 317-2 PN/DP, CPU 319-3 PN/DP) or a separate CP 343-1 communications processor for TCP/IP-based engineering access. The engineering station (PG/PC) running STEP 7 V5.x or TIA Portal joins the same IPv4 subnet as the CPU and uses the PG/PC Interface assignment to route the S7 protocol over the PC's NIC.

Unlike PROFIBUS (MPI/DP) where the PG address is bound to the PROFIBUS node and must be unique, Ethernet communication is governed by two simple rules: the PG/PC and the S7-300 CPU must share the same subnet mask, and no two nodes may carry the same IPv4 address. When either rule is violated, STEP 7 raises a connection error and the Accessible Nodes view returns an empty list.

Note: The PROFINET interface on the S7-300 is backward-compatible with standard TCP/IP. STEP 7 still calls the assignment "Ethernet" or "TCP/IP" in older projects even though the physical port is PROFINET (X1, RJ45, 100 Mbit/s full duplex).

Prerequisites

• STEP 7 V5.5 + SP2 or higher, or TIA Portal V13+ with the S7-300 HSP (Hardware Support Package).
• Original STEP 7 project (or a project that contains the offline hardware configuration of the target CPU). Without the project, only "Accessible Nodes" works and online editing is limited.
• Known IPv4 address and subnet mask of the CPU's PROFINET/CP interface, read either from the project (HW Config → Properties → Ethernet) or from a previous project archive.
• RJ45 patch cable (straight-through for switch, crossover for direct PG↔CPU; most modern NICs auto-MDI/MDIX so a single straight cable is sufficient).
• Administrator rights on the engineering station to modify the TCP/IP stack and to set the PG/PC interface.
• Windows firewall rule allowing S7ONLINE (TCP/102) and ISO-on-TCP (TCP/102 + TCP/TCP/UDP) outbound traffic.

PG/PC Interface Configuration in SIMATIC Manager

The Set PG/PC Interface tool binds STEP 7 to a specific Windows access point. The two relevant access points for Ethernet work are S7ONLINE (STEP 7) → TCP/IP and (for older SIMATIC NET installations) S7ONLINE → ISO Ind. Ethernet.

1. Close SIMATIC Manager.
2. Open the Windows Start menu and launch Set PG/PC Interface (Start → SIMATIC → STEP 7 → Set PG/PC Interface).
3. In the Interface Parameter Assignment Used list, expand S7ONLINE (STEP 7).
4. Select the entry that matches the NIC you will use, e.g. TCP/IP → <your NIC>.TCPIP.1.
5. Click OK. The system stores the assignment in the registry under HKLM\SOFTWARE\Siemens\AUTSW\S7ONLINE\Interfaces.

Assigning the Engineering Station IP Address

The IPv4 parameters of the PC NIC must be in the same subnet as the CPU. Siemens' default plant network convention (also visible in the example IP from the field case: 10.10.0.x) is to use one Class-A private range across the plant and to reserve a fixed address for every device.

To assign the IP under Windows:

1. Control Panel → Network and Sharing Center → Change adapter settings.
2. Right-click the NIC → Properties → Internet Protocol Version 4 (TCP/IPv4) → Properties.
3. Select Use the following IP address.
4. Enter IP, mask, and gateway from the table above.
5. Click OK on both dialogs.

Verify the assignment with a command prompt:

ipconfig /all
ping 10.10.0.10

A successful ping (4/4 replies, <1 ms on a direct link) confirms Layer 3 reachability. If ping fails, the issue is physical or lower-layer, not STEP 7.

Bringing the CPU Online

1. Open the project in SIMATIC Manager.
2. Right-click the S7-300 station → Open HW Config.
3. From the menu PLC → Ethernet → Edit Ethernet Node or the toolbar button Ethernet Node. STEP 7 broadcasts a DCP Identify request on the configured NIC. The CPU returns its MAC, IP, and PROFINET device name.
4. If the node is not listed, click Browse on a directly connected CPU by typing the IP address into the Node address field and pressing Enter. The CPU replies through its PROFINET interface.
5. Click OK to confirm, then close the dialog. HW Config now resolves the partner.
6. From the menu PLC → Download to Target Device (or Ctrl+L) to download hardware configuration. Alternatively, PLC → Online → Go Online opens the online view without modifying the CPU.

Resolving the "Set Local Node Address Is Already in Use" Error

The error message Online: the set local node address is already in use occurs when STEP 7 tries to bind the S7-Online protocol stack to an IP address that another process on the PC is already using. This is the most common Ethernet access error and is independent of the CPU's IP: it is reported by the local TCP/IP stack.

1. Open Set PG/PC Interface and select S7ONLINE (STEP 7) → TCP/IP → <correct NIC>.
2. Close SIMATIC Manager completely.
3. Open a command prompt as Administrator and run:
   net stop s7onlinesvc & net start s7onlinesvc (or simply reboot the PG).
4. Verify with netstat -ano | findstr :102 that no stale process is bound.
5. Restart STEP 7 and try Accessible Nodes again.

Accessible Nodes vs. Project-Online

STEP 7 supports two distinct online paths:

When a new project is created for an unknown CPU, use Accessible Nodes first to identify the device, then Upload Station to PG (PLC → Upload Station to PG) to build a matching offline project.

Loading and Verifying the Program

1. Confirm Accessible Nodes shows the CPU's IP and a green status icon.
2. From the project, right-click the S7 program → Download. The S7-300 transfers OB, FB, FC, DB, SDB, and SFC blocks to the CPU's load memory.
3. Open the online view: PLC → Online → Go Online. STEP 7 displays RUN, STOP, or HOLD in the status bar.
4. Switch the CPU to RUN-P from PLC → Operating Mode to start the user program. RUN-P allows both program execution and online editing; RUN blocks online write attempts.
5. Open a block in online view, right-click → Monitor/Modify to view tags live.
6. Use PLC → Diagnostic → Diagnostic Buffer to confirm no startup faults are present (typical error IDs: SF LED on → SF in the diagnostic buffer with event ID 0x0001 through 0x00FF).

Common S7-300 Ethernet Fault Codes and Indicators

Switch and Network Considerations

For a single PG↔CPU link, a direct cable is sufficient. Once a switch is introduced, observe these constraints:

• Use a managed switch with PROFINET QoS (DSCP priority 6 for PROFINET RT frames) when real-time I/O shares the network with engineering traffic.
• Disable Energy Efficient Ethernet (EEE, IEEE 802.3az) on the switch port. S7-300 PROFINET interfaces do not negotiate EEE and the link may drop intermittently.
• Set the switch port to 100 Mbit/s full duplex, auto-negotiation off, if you observe CRC errors on the CPU's port statistics (PN X1 diagnostics → Port statistics).
• Avoid daisy-chaining PROFINET devices with office-grade switches that drop broadcast storms. PROFINET uses LLDP for topology; unmanaged switches do not propagate LLDP correctly and may break device replacement without re-assignment.

Migration Path: STEP 7 V5.x to TIA Portal

Existing S7-300 Ethernet projects can be migrated to TIA Portal V16+ via Project → Migrate project. The PROFINET interface IP, subnet, and device name migrate unchanged. The PG/PC interface in TIA Portal is bound per project under Online → Accessible devices and is no longer global. After migration, perform an Upload device to PG as a verification step and compare block checksums against the legacy archive.

Verification Checklist

• ipconfig /all shows the PG IP and the correct subnet mask.
• ping <CPU IP> returns <1 ms with 0% loss on a direct link.
• STEP 7 Set PG/PC Interface shows S7ONLINE (STEP 7) → TCP/IP → <NIC>.
• SIMATIC Manager Accessible Nodes lists the CPU with the correct IP and module order.
• Project online view shows the CPU in RUN or RUN-P after download.
• Diagnostic buffer contains no entries with ID 0x2520 (IP duplicate) or 0x2530 (PROFINET name missing).
• User program executes: a forced output or a tag monitor confirms scan cycle progress.

FAQ