Resolving LOGO! 8 to TP900 Comfort HMI Connection Drops in TIA

1. Problem Overview

A LOGO! 8 controller (article number 6ED1 052-1CC01-0BA8) is networked to a SIMATIC TP900 Comfort HMI (6AV2 124-0JC01-0AX0) through a TIA Portal V16 project. After downloading to the panel, the runtime alternates between two messages on a short loop:

• Connection established
• Connection disconnected

The cycle repeats every few seconds, the HMI cannot read process tags, and no fault is raised in the LOGO! itself. The fault is purely in the HMI communication stack and is the classic symptom of a LOGO! driver / firmware mismatch in WinCC Comfort/Advanced on TIA Portal V16.

2. Hardware Identification

Exact article numbers are mandatory when diagnosing LOGO! / HMI communication. The same part number can be shipped with different firmware loads, and the WinCC driver must be matched to the actual firmware that is running on the device.

Verify the article number printed on the front of the LOGO! (lower-left of the device, behind the removable flap) against the version reported in LOGO! → Diagnostics → Device Information → Version. A 0BA8 module can carry any of the firmware trains listed below.

3. The 0BA8 Standard vs 0BA8.FS4 Distinction

The article number 6ED1 052-1CC01-0BA8 does not uniquely identify a single firmware generation. Siemens reused the same MLFB for at least two firmware trains:

When TIA Portal V16 was released, the LOGO! 8.FS4 support had to be added via a HSP (Hardware Support Package). The shipped "SIMATIC LOGO! 8" device in the HMI catalog only knows the 0BA8 Standard protocol. Loading the FS4 firmware on a 0BA8 module and then using the standard driver yields exactly the symptoms described: the panel opens a TCP session on port 102, the LOGO! accepts the COTP connection, the S7 setup PDU is rejected, and the panel immediately retries - which the user sees as a continuous connection established / disconnected cycle.

4. Network and Project Prerequisites

Before opening TIA Portal, validate the underlying network so that the panel and the LOGO! can at least see each other at TCP level.

1. Both devices on the same IP subnet, e.g. 192.168.0.1 / 24 for the LOGO! and 192.168.0.10 / 24 for the TP900. Default LOGO! address is 192.168.0.1; default TP900 is 0.0.0.0 (DHCP) until set in the project or on the panel's Control Panel → Network.
2. Subnet mask 255.255.255.0 on both.
3. No VLAN tagging - LOGO! 8 does not support tagged frames. Comfort panels can tag; disable tags on the HMI port or match the LOGO! port to a port-based VLAN.
4. No managed switch blocking ISO-TSAP (TCP/102). Some industrial firewalls block S7 by default; allowlist port 102 between HMI and LOGO!.
5. Update the TP900 Comfort image to the latest Windows CE / WinCC Runtime image for V16 (see TIA V16 update downloads). Older images can refuse PDU 2.0 setups from newer LOGO! firmware.

4.1 Quick reachability test

From the engineering PC run a single ping and an ISO-TSAP probe before touching the project:

ping 192.168.0.1
nmap -p 102 192.168.0.1

A successful reply on port 102 confirms the LOGO! is online and the rack is exposed; it does not confirm driver compatibility.

5. LOGO! Soft Comfort 8.2 Network Project Configuration

Open LOGO! Soft Comfort 8.2, create or open the project, and confirm the network parameters. The HMI does not require a passive S7 connection to be created in LSC - the LOGO! always answers the panel's active COTP CR packet on port 102.

1. Tools → Ethernet Connections (or the network view in the newer ribbon UI). Add the TP900 as a new device and assign the IP 192.168.0.10. Save.
2. Tools → Transfer → PC <-> LOGO! → Configure Network. Set the LOGO! IP, subnet, and gateway. Allow S7 access from external devices must remain enabled - the default is on, but it is the most common reason for "HMI shows connected, no tags updating" in older service calls.
3. Program a simple marker in the LOGO! program that is not linked to the I/O - for example a flag set by the on-board cursor key. This proves tag visibility once the HMI connects.
4. Download to the LOGO!. Confirm with Online view that the firmware version reads 0BA8 Standard or 0BA8.FS4.

6. TIA Portal V16 HMI Configuration

6.1 Insert the TP900 and the LOGO!

1. Open the TIA Portal V16 project. Add a SIMATIC TP900 Comfort from the device catalog (HMI → Comfort Panels → 9" → TP900).
2. Add the LOGO! as a SIMATIC LOGO! 8 (not 0BA7). The article 6ED1 052-1CC01-0BA8 should appear in the catalog once the LOGO! 8 HSP is installed.
3. Drag the HMI's PROFINET port to the LOGO! Ethernet port in the Devices & Networks view. A green S7 connection is created automatically.

6.2 Configure the S7 connection

Open the S7 connection properties and verify:

6.3 Select the correct HMI driver

This is the step that resolves the original fault. In TIA Portal V16 the HMI catalog contains a separate device entry per LOGO! firmware train:

• SIMATIC LOGO! 8 - for 0BA8 Standard firmware (8.0 - 8.2)
• SIMATIC LOGO! 8.FS4 - for 0BA8.FS4 firmware (8.3 - 8.4)

If the device was inserted as "SIMATIC LOGO! 8" but the hardware is actually running 0BA8.FS4, change the device and module version:

1. Select the LOGO! in the project tree, open Properties → General → Device.
2. In the Catalog pane on the right, search for LOGO! 8.FS4. The 6ED1 052-1CC01-0BA8 FS4 variant is listed separately.
3. Drag it onto the existing module, confirm the Change device dialog. TIA will rewrite the connection parameters and the supported tag set.

7. Root Cause and Fix Summary

8. Verification Procedure

1. Compile the HMI project. TIA V16 should report No errors; warnings about LOGO! 8 protocol limits can be ignored.
2. Download to the TP900 Comfort. Use Ethernet, not USB, for the first attempt so that the boot image and runtime are both updated.
3. Watch the panel boot into WinCC Runtime. The status bar should settle on Connection established within 5 s and remain.
4. Toggle the test marker created in step 5.3 of the LSC project. The value should update on the panel inside one refresh cycle (default 1 s for acquisition cycles of 100 ms - 1 s on LOGO! 8).
5. Open LOGOI Webserver (browser to http://192.168.0.1) and check the Connected clients list. The TP900 should appear as a single S7 connection.

9. Inline Diagnostic Flow

10. Best-Practices Checklist

• Always read the LOGO! firmware version and write it on the project cover sheet. The 0BA8 Standard / 0BA8.FS4 split is the single most common 0BA8 connection fault in the field.
• Use one fixed IP per LOGO! and one fixed IP per Comfort panel. Avoid DHCP for production panels.
• Set the HMI acquisition cycle to 1 s as a baseline. Faster cycles (100 - 250 ms) work but generate heavier S7 traffic on the LOGO! and can overflow the 8-connection limit if multiple HMIs are added.
• Do not create a passive S7 connection in LSC for the panel. The LOGO! is the server; the panel is the client.
• Add a simple I/O checkbox or numeric I/O field to the HMI first screen during commissioning. It gives the maintenance crew a visible "is the HMI alive?" tag without opening the LOGO! housing.

11. Compatibility Matrix (TIA V16)

12. Safety and Operational Notes

13. FAQ