Resolving WinCC flexible 2008 S7-300 Ethernet Connection Errors

Problem Overview: WinCC flexible 2008 to SIMATIC S7-300 Ethernet Link

Engineers commissioning HMIs on legacy installations still routinely encounter WinCC flexible 2008 SP5 (the last released service pack of the classic flexible engineering suite) paired with a SIMATIC S7-300 CPU (CPU 315-2 PN/DP, CPU 317-2 PN/DP, CPU 319-3 PN/DP, plus the CP 343-1 Lean/Advanced/IT family on older 31x devices). The most common reported symptom is a runtime alarm of the form "Connection is cut" or "No connection to PLC" on a TP177B, TP277, MP277, or PC-based WinCC flexible Runtime panel. A secondary symptom is the WinCC flexible connection editor displaying the interface as "IE general" instead of the expected "Ethernet" NIC label, which makes the project portable only on machines where the same NIC GUID is present.

This reference documents the root-cause matrix, the exact STEP 7 V5.5 + WinCC flexible 2008 SP5 configuration steps for both direct Ethernet and WAN / Ethernet-modem / VPN paths, the verification procedure, and the migration path to TIA Portal V20 for installations that are at end-of-life for the legacy tools.

Root-Cause Matrix for "Connection is cut" / "IE general" Errors

Prerequisites

• STEP 7 V5.5 + SP4 or higher with the optional HSP for the S7-300 CPU installed (HSPs are listed in the STEP 7 V5.5 Hardware Support Package overview).
• WinCC flexible 2008 SP5 (build 13.0.4.0 or higher). The SP5 image is available from legacy media; SP5 is the final SP and the minimum revision that cooperates correctly with Windows 10 LTSC if you are using a WinCC flexible Runtime PC.
• For the CPU firmware: minimum recommended is V3.3 for CPU 31x PN/DP (e.g. 6ES7315-2EH14-0AB0 / FW 3.3) and V2.4 for the CP 343-1 family. Earlier firmware on the CP 343-1 exhibits the well-known connection resource exhaustion fault when more than four S7 connections are opened simultaneously.
• Ethernet switch or crossover cable, plus sufficient S7 connection resources on the CPU (a 315-2 PN/DP reserves 14 connection resources; a CP 343-1 reserves 16; reserve at least one PG, one OP, and one passive S7).

Solution Path A — Direct Ethernet (Same Subnet)

This is the recommended topology for commissioning, troubleshooting, and proof-of-concept. Remove the modem from the path until step 4 verifies.

Step 1 — Configure STEP 7 IP addresses

1. Open SIMATIC Manager and load the S7-300 station.
2. Open HW Config and double-click the PROFINET interface of the CPU (or the CP 343-1).
3. Assign IP address 192.168.1.1, Subnet mask 255.255.255.0, leave Router blank for the direct path.
4. Download the hardware configuration (target system → PC → CPU).
5. Open NetPro and confirm that the PROFINET interface has at least one S7 connection of type S7 connection. If not, right-click the CPU/CP and select Insert New Connection → S7 connection → (unspecified); this creates the connection resource the HMI will consume.

Step 2 — Configure the HMI IP address

1. On the HMI panel, open Control Panel → Network & Dial-up Connections (TP/MP 277 and earlier) or Settings → Network (Comfort panels with WinCC flexible 2008 SP5 runtime).
2. Assign 192.168.1.2 / 255.255.255.0.
3. Save and reboot the panel.

Step 3 — Configure the WinCC flexible connection

1. In the WinCC flexible project, open Connections in the project tree.
2. Double-click the existing Ethernet connection (or right-click → New Connection).
3. Set Communication driver = SIMATIC S7 300/400.
4. Set HMI device → Interface = Ethernet. If the dropdown only shows IE general, switch to the integrated project workflow (see Solution Path C).
5. Set PLC → Address = 192.168.1.1.
6. Set PLC → Expansion slot = the slot number of the PROFINET interface (typically 2 for an integrated PN CPU, X for a CP 343-1 where X is the slot in the rack).
7. Set Connection = the S7 connection created in NetPro. If you left NetPro on (unspecified), leave this field on None / automatic.

Step 4 — Set the PG/PC interface

1. Close SIMATIC Manager.
2. Open Control Panel → Set PG/PC Interface (32-bit) on the engineering PC.
3. For S7ONLINE access point, select <Physical NIC>.TCPIP.1, not TCP/IP (Auto).
4. Click OK. The interface is now bound.

Step 5 — Transfer and verify

1. Compile the WinCC flexible project (Project → Compiler → All) and transfer it to the panel (Project → Transfer → Ethernet, then Start on the panel and confirm).
2. On the panel, open Start Center → Settings → System → Ethernet → Status. The connection icon should turn green within ~5 s.
3. From the engineering PC, open S7 Diagnostic (Start → SIMATIC → S7-PCS7 → S7-Diagnose). Click Online → Accessible Nodes. The CPU at 192.168.1.1 should appear with MAC and firmware revision.
4. From the HMI, toggle a tag (e.g. M0.0 in the PLC) and confirm the change reflects in the WinCC flexible screen.

Solution Path B — WAN / Ethernet-Modem with VPN Tunnel

For remote sites where the HMI must reach the S7-300 over a WAN modem, cellular router, or radio bridge, the S7-300 must be reachable as if it were on the same subnet. The native Siemens approach is the S7-300 with CP 343-1 IT communicating through an IPsec VPN tunnel terminated on the remote modem/router. Direct Internet exposure of port 102 is not recommended and is blocked by most site firewalls.

Step 1 — Confirm the link layer

1. From a laptop attached to the WAN modem, ping 192.168.1.1. If the ping fails, the problem is modem / ISP / APN, not the HMI.
2. Test the S7 port: telnet 192.168.1.1 102. A blank screen or a banner indicates the PLC is reachable; connection refused or timeout indicates the firewall is dropping ISO-on-TCP.

Step 3 — Build the IPsec tunnel

1. On the WAN modem/router at the PLC site, configure an IPsec site-to-site tunnel. Use IKEv2 with AES-256/SHA-256 unless the modem firmware caps at IKEv1/AES-128.
2. Define the remote subnet as 192.168.1.0/24 and the local (PLC) subnet as the modem's LAN, typically the same 192.168.1.0/24. If the two LANs use the same subnet, the modem must NAT the remote side to a different subnet (e.g. 10.10.10.0/24) and the HMI/panel must be reconfigured to the routed address.
3. Open UDP 500, UDP 4500, and (for NAT-T) ESP protocol 50/51. Do not open TCP 102 directly to the public Internet.

Step 4 — Reconfigure the HMI

1. On the panel, set the default gateway to the local WAN modem IP (e.g. 192.168.2.1) and DNS to the tunnel endpoint if name resolution is needed.
2. In WinCC flexible, set PLC Address to the tunneled address of the S7-300 (the address the modem presents to the HMI side, typically 10.10.10.1 after NAT).

Step 5 — Tune the polling cycle

1. In WinCC flexible, raise the acquisition cycle for low-priority tags to 2 s or 5 s. Default 1 s polling over a 256 kbit/s radio modem saturates the link and triggers the modem's idle timeout.
2. Open Connections → Area pointer and confirm the coordination area pointer is enabled; this lets the panel re-establish the connection after a brief link drop without a full restart.

Step 6 — Verify

1. From the panel, Start → Settings → Network → Ping (if the panel firmware supports it) or run ping from a laptop connected to the HMI-side modem.
2. Watch the VPN tunnel status on both modems; tunnels typically re-key every 8 hours. A momentary drop during rekey is normal; sustained drops indicate a Phase 2 mismatch.

Solution Path C — Integrated Project (STEP 7 + WinCC flexible on the Same PC Station)

The integrated workflow removes the IE general placeholder and is the only workflow Siemens officially supports for WinCC flexible 2008 + STEP 7 V5.5. The project must be opened via SIMATIC Manager → Options → WinCC flexible → Open Project, not by launching WinCC flexible standalone.

1. In SIMATIC Manager, right-click the S7-300 station and choose Insert New Object → SIMATIC HMI Station.
2. Pick the panel type (e.g. TP177B 6" PN/DP, order code 6AV6642-0BA01-1AX1).
3. Right-click the HMI station and choose Open in WinCC flexible. SIMATIC Manager and WinCC flexible now share a single NetPro database.
4. In NetPro, drag a connection from the HMI to the CPU. WinCC flexible auto-populates the IP and slot.
5. Compile and download the entire PC station (S7-300 + HMI) in one transaction.

Verification Checklist

Troubleshooting Matrix (Symptom → Cause → Fix)

Migration Path to TIA Portal V20

WinCC flexible 2008 SP5 reached end of life in 2018 and STEP 7 V5.5 reached end of life in 2020. New installations should use TIA Portal V20 with WinCC Comfort/Advanced. Existing projects can be migrated using the migration tool described in the Migrating WinCC flexible 2008 projects to TIA Portal reference. Key points:

• STEP 7 V5.5 projects are migrated to a TIA Portal V20 project; the S7-300 program is converted in-place (OB1, FB/FC, DB blocks remain), but DB addresses can be renumbered if the project contains absolute DB accesses.
• WinCC flexible HMI stations are migrated to the equivalent Comfort panel (e.g. TP177B → KTP700 Comfort, TP277 → TP900 Comfort).
• Migration of project texts is automatic for S7-300/400 and the HMI; alarm texts are re-mapped to the TIA alarm class model.
• Connection configurations are preserved: S7 connections with IP 192.168.1.1/2 transfer as-is. IE general placeholders are resolved during migration.
• Validate the migrated project on the Target system simulation before downloading to the panel.

Connection Resource Budget Reference

For each active HMI connection, the CPU reserves one resource. If the CPU diagnostic buffer shows SF LED with "No more connection resources available", reduce the number of HMI panels per CPU, or split the topology across a CP 343-1 Advanced with its own resource pool.

Frequently Asked Questions