Siemens LOGO! 0BA8 Communication Port Configuration and PC Integration

The Siemens LOGO! 0BA8 (order suffix 6ED1052-1MD08-0BA0 for the LOGO! 12/24 RCE variant) integrates a programmable logic relay with a built-in Ethernet interface. Unlike its predecessors, the 0BA8 generation can communicate over TCP/IP using both a web-based user interface and S7-compatible protocol frames. A common engineering question concerns the fixed nature of the LOGO! communication port: the device does not expose a parameter for changing the listening TCP port, but engineers can still reach the LOGO! from a Visual Studio application through the port-forwarding technique documented below.

1. Hardware Identification: 0BA0 vs 0BA8

The Siemens order-number convention for the LOGO! 8 series ends with the generation suffix. The trailing four characters encode both the production batch and the hardware generation:

The label 6ED1052-1MD08-0BA0 contains the production code 08 immediately before the 0BA0 suffix. That embedded 08 identifies the device as a 0BA8 (LOGO! 8) unit. The final four characters (0BA0) are an internal production/firmware designator, not a generation marker. This is a frequent source of confusion: the device is a LOGO! 8, not a LOGO! 0BA0 (LOGO! 6). Confirming the generation is essential because only the LOGO! 8 (0BA8) supports TCP/IP-based S7 communication on the integrated RJ45 port.

2. LOGO! 0BA8 Communication Architecture

The LOGO! 8 integrates an Ethernet switch with two RJ45 ports, allowing daisy-chained network topologies without additional hardware. The controller exposes several communication endpoints simultaneously:

The web server on port 8080 is non-standard (default HTTP is port 80) and was chosen to avoid conflicts with corporate firewalls and IIS installations. The S7 communication on port 102 follows the ISO-on-TCP standard (RFC 1006) used across the SIMATIC family. Both ports are hard-coded in the LOGO! firmware; the device does not provide a configuration parameter to remap them.

3. Why Port Numbers Cannot Be Changed on the LOGO! Itself

The LOGO! 0BA8 firmware does not expose a user interface for port remapping. Reasons include:

1. Fixed firmware implementation: The TCP listener sockets are bound during firmware initialization. There is no retained parameter slot in the LOGO! configuration tree for TCP port numbers.
2. LOGO! Soft Comfort dependency: The programming tool (LOGO! Soft Comfort V8.x or later) discovers the device and opens a connection on the standard port 8080. Changing the port would break the discovery mechanism unless the tool were updated in lockstep.
3. Memory constraints: The LOGO! has limited configuration storage. Adding port-mapping parameters would consume resources better allocated to the program and data blocks.
4. Web-server port collision avoidance: Port 8080 was selected specifically as a non-privileged alternative to port 80 to prevent issues with corporate web servers. The port is part of the product specification, not a user preference.

When a Visual Studio sample (e.g., the LOGO! self-installer that ships with the LOGO! 0BA8 documentation) attempts to connect to port 10001, it cannot establish a session because the LOGO! is not listening on that port. The sample assumes a forwarded port has been set up at the network boundary, not that the LOGO! itself listens on 10001.

4. Port Forwarding Architecture

The canonical solution is to place a small router (a separate, dedicated routing device) between the engineering PC's network and the LOGO!. The router's WAN-side port is configured to forward the desired external port to the LOGO!'s internal port. The LOGO! itself is not modified.

4.1 Typical Topology

4.2 Step-by-Step Router Configuration

1. Assign the LOGO! a static IP via the LOGO! menu: Network → IP Address set to 192.168.1.10, subnet mask 255.255.255.0, gateway 192.168.1.1. Disable DHCP on the LOGO! to prevent address drift.
2. Connect the dedicated router's LAN port directly to the LOGO!'s RJ45 port using a standard Cat5e/Cat6 patch cable.
3. Configure the dedicated router's LAN side with IP 192.168.1.1, subnet 255.255.255.0, and disable its built-in DHCP server (the LOGO! has a fixed address and no other clients are needed on this segment).
4. Configure the dedicated router's WAN side as a DHCP client if the engineering network provides addresses, or as a static address (e.g., 192.168.2.99, gateway 192.168.2.1) if the engineering network uses static addressing.
5. Add port-forwarding rules on the dedicated router:
   • External port 10001 → internal 192.168.1.10:8080 (HTTP web server / programming)
   • External port 10002 → internal 192.168.1.10:102 (S7 communication)
6. Update the Visual Studio application connection string or socket creation call to point at 192.168.2.99:10001 (or :10002 for S7 data exchange).
7. Test connectivity from the engineering PC using telnet 192.168.2.99 10001 or by browsing to http://192.168.2.99:10001 in a browser to confirm the LOGO! web UI loads.

5. Visual Studio Integration

Siemens does not provide a first-party .NET library for LOGO! 0BA8 communication. Two open-source libraries are commonly used:

5.1 Connection String in S7.NET

The S7.NET library uses a CpuType enumeration. For LOGO! 0BA8, select CpuType.Logo0BA8 (compatibility mode). The connection example below targets the forwarded port:

using S7.Net;

var plc = new Plc(CpuType.Logo0BA8, "192.168.2.99", 10002, 0, 0);
plc.Open();

// Read a variable block (DB1) at byte 0, length 16 bytes
byte[] buffer = plc.ReadBytes(DataType.DataBlock, 1, 0, 16);

// Write a single bit
plc.WriteBit("DB1.DBX0.0", true);

plc.Close();

Note that port 10002 in the example is the externally forwarded port; the library sends frames on whichever port the connection specifies. The router translates 10002 to internal 102 transparently.

5.2 Reading Web-Server Variables via HTTP

The LOGO! 0BA8 web server exposes a JSON-like variable table at http://<ip>:8080/<variable-tag>. The Visual Studio sample included with LOGO! Soft Comfort uses HttpClient with the redirected port:

using System.Net.Http;

var client = new HttpClient { BaseAddress = new System.Uri("http://192.168.2.99:10001") };
string response = await client.GetStringAsync("/LOGO!+Variable+Table");
// Parse response for tag values

6. Network Configuration on the LOGO!

Configure the LOGO! network parameters from the device's onboard display or via LOGO! Soft Comfort V8.x:

The LOGO! 0BA8 does not support DHCP client functionality. The device must be assigned a static IP. This design choice is intentional to keep the device predictable on industrial networks where address stability matters for alarm routing and tag-name resolution in SCADA systems.

7. Direct Connection Without a Router

If the engineering PC is on the same subnet as the LOGO!, no port forwarding is required. The PC can connect directly using the LOGO!'s real IP and port:

• Web UI: http://192.168.1.10:8080
• S7 communication: 192.168.1.10:102
• LOGO! Soft Comfort online mode: 192.168.1.10 (default port 8080)

This direct connection works when both devices share a subnet and no NAT boundary exists between them. For example, a laptop connected directly to the LOGO!'s second Ethernet port (the 0BA8 has two RJ45 jacks in a built-in switch) using a crossover or modern auto-sensing patch cable.

8. Windows COM Port Considerations

If the engineering PC does not have a free Ethernet port and the application is constrained to serial communication, the LOGO! 0BA8 still requires Ethernet. The legacy LOGO! generations (0BA0 through 0BA6) used a proprietary PC-COM cable for LOGO! Soft Comfort programming. The 0BA8 replaced this with Ethernet. If the engineering PC only has COM ports available, configure a USB-to-Ethernet adapter and assign it a static IP in the LOGO! subnet. Windows COM-port configuration details are documented at Microsoft Learn: Communication Port Settings; however, the COM port configuration is unrelated to the LOGO!'s TCP listener. The two are separate physical interfaces.

9. Troubleshooting Matrix

10. Verification Procedure

After configuring the port-forwarding setup and the Visual Studio application, validate each layer of the stack:

1. Physical layer: Confirm LINK LEDs are lit on both the LOGO! RJ45 ports and the router LAN port. Replace the patch cable if no link is established.
2. Network layer: From the engineering PC, ping the router WAN address (192.168.2.99), then ping the LOGO! address (192.168.1.10) from a second PC on the LOGO! segment. Both should respond.
3. Forwarding layer: From the engineering PC, open a browser to http://192.168.2.99:10001. The LOGO! web UI must load. If it does, the 8080 forwarding rule is correct. Repeat for port 10002 with a S7 client tool.
4. Application layer: Run the Visual Studio application. Verify that it opens the connection without throwing ConnectionRefused or SocketTimeout, and that read/write operations return expected values.
5. LOGO! Soft Comfort online test: Open LOGO! Soft Comfort V8.x or later, select Tools → Transfer → Online Test, and confirm the LOGO! is discovered at the forwarded IP and port.

11. Field-Commissioning Notes

• Document the forwarding rules: When a maintenance engineer needs to access the LOGO! in two years, the port-forwarding map should be in the cabinet documentation. A one-line note like "Router WAN port 10001 → LOGO! 192.168.1.10:8080" saves hours of troubleshooting.
• Use a dedicated, managed router: Consumer-grade "travel routers" work but often lack NAT timeout controls and have aggressive idle disconnects. Industrial firewalls (e.g., Siemens SCALANCE, Phoenix Contact mGuard) support deterministic NAT.
• Lock the LOGO! configuration: Once the network settings are correct, set a LOGO! program password to prevent accidental changes from the device menu.
• Avoid double-NAT: If the engineering network already uses NAT at its boundary, adding a second NAT layer at the LOGO! can break discovery. Use routable addressing or place the dedicated router in bridge mode where possible.
• Monitor NAT sessions: Some routers log dropped sessions. If the S7 connection drops during long-running operations, the router may be aging out the NAT entry. Configure TCP keep-alives in the .NET application to maintain the session.

12. Frequently Asked Questions