Troubleshooting Siemens HMI Not Connecting to PLC in TIA Portal

Troubleshooting Siemens HMI Not Connecting to PLC in TIA Portal V13

When a second Siemens HMI is added in parallel to an existing KEB panel and the new device refuses to communicate with the S7 PLC, the failure almost always traces back to the HMI connection inside the TIA Portal project, not to a damaged cable. TIA Portal V13 (now legacy) is a fully integrated engineering suite, and every operator panel must be wired to a CPU through a defined HMI connection that maps a PLC interface to a panel interface and binds the data exchange. If that connection is missing, the HMI compiles, downloads, and starts up showing a system error or "Connection interrupted" alarm — the classic symptom of a project that compiles correctly but has no runtime path between panel tags and the controller's data blocks.

This reference walks through the engineering decisions, parameter settings, and verification steps required to bring the second HMI online, and it complements the official Siemens application summary "How do you configure an HMI connection between an HMI and a controller in the TIA Portal?" with field-tested diagnostics for the TIA V13 era.

1. Problem Description

The reported symptom is straightforward:

• Existing KEB HMI is online and exchanging process data with the S7 PLC.
• A new Siemens Comfort or Basic Panel is inserted in Devices & Networks and linked to the same S7 CPU.
• The Siemens HMI downloads, starts the runtime, but does not display live values from the PLC.
• No connection status "Connected" indicator is shown in the HMI runtime, or the panel shows the message Connection interrupted: HMI_1 [Connection 1].
• The WinCC flexible / WinCC (TIA) alarm buffer may record event 140001 or 190001 referencing the missing HMI connection.

This applies to S7-300, S7-400, S7-1200, and S7-1500 stations. Although TIA Portal V13 is outdated, the connection-handling logic is identical to V15, V16, and V17. The fix shown here also applies when migrating from legacy WinCC flexible 2008 SP5 projects.

2. Root Cause Analysis: Why the HMI Fails to Connect

Connection failures between a Siemens panel and an S7 controller fall into five distinct categories. In a TIA Portal V13 project, the second HMI typically fails because the engineer created the HMI device but never created the HMI connection object that links the HMI's interface to the PLC's interface.

The first category — missing HMI connection — accounts for the majority of "HMI don't connect to PLC" tickets on S7-300 and S7-400 systems where the second HMI is added to a project that was originally built without it. TIA Portal does not auto-create a connection; the engineer must right-click Connections and choose Add new connection.

3. Prerequisites and Required Information

Before opening the project, gather the following:

• PLC order number (e.g. 6ES7 315-2EH14-0AB0) and firmware version visible in Online & Diagnostics > Diagnostic information.
• HMI order number (e.g. 6AV2 124-1MC01-0AX0 TP1200 Comfort) and panel firmware version.
• Existing KEB HMI model and the protocol it uses to the PLC (PROFINET, PROFIBUS, or Modbus-TCP).
• Project file location and the TIA Portal V13 SP1 (or V13 Update 9) installation used to compile the project.
• IP addresses and PROFINET device names already assigned to the PLC, the KEB HMI, and the engineering PG/PC.
• Network topology: switch model, cabling (Cat 5e minimum for PROFINET), and any router/NAT device.

4. Step-by-Step: Configuring the HMI Connection in TIA Portal V13

1. Open the TIA Portal V13 project that contains the S7 PLC and the existing KEB HMI.
2. In the project tree, expand Devices & Networks and double-click Network view.
3. Drag the new Siemens HMI from the hardware catalog (right pane) into the network view. The catalog is sorted under HMI > SIMATIC Comfort Panels or Basic Panels depending on the device.
4. Click the Connections button on the toolbar to enter connection mode. The cursor changes to a hand with a plug.
5. Click the PROFINET interface port of the new HMI and drag a connection line to the PROFINET interface of the S7 CPU. TIA Portal will automatically create an HMI connection object under the HMI and bind it to the PLC's interface.
6. If the PLC and HMI are on different subnets, drop a PROFINET IO subnet between them. TIA Portal will assign a default subnet name like PN/IE_1.
7. Click the new connection line and verify in the inspector window under Properties > General > Connection that the Endpoint 1 shows the HMI and Endpoint 2 shows the correct PLC interface (typically PLC_1 > PROFINET interface_1).
8. Right-click the HMI in the project tree, choose Properties > General > Connection, and confirm the connection is listed as Active and Online.
9. Save the project (Ctrl+S), then select the HMI and click Compile > Software (rebuild all).
10. Download to the HMI: right-click the HMI → Download to device > Software and configuration. Confirm the PG/PC interface matches the network adapter connected to the HMI.
11. When the panel restarts, the runtime will start with the new connection active. Verify in the HMI's system screen under System information > Connections that the status is Connected.

If a connection object already exists but the panel still cannot see the PLC, jump to Section 7 — Network Configuration to validate IP addresses, device names, and subnet masks.

5. HMI Connection Types and Selection

For SIMATIC S7 controllers, TIA Portal V13 supports the following HMI connection types. The correct type depends on the CPU's available interfaces and the network infrastructure.

6. PLC Project Setup for the New HMI

The PLC side must be configured to accept the S7 connection from the HMI. For S7-300/400 CPUs:

1. Open PLC_1 > Properties > General > Protection.
2. Choose Full access (no protection) if the plant security policy allows it. Otherwise select Access protection and set a password for the HMI account.
3. Open PLC_1 > Properties > General > Connection resources. Each S7-1200/1500 supports 16 S7 connection resources; S7-300 PN/DP supports up to 16. Each HMI consumes 1 connection resource for its primary connection plus 1 for each additional connection (e.g. alarm connection).
4. Confirm the KEB HMI + new Siemens HMI + PG/PC + any other consumer does not exceed the available count. If exhausted, the new HMI will be denied without an explicit error.
5. Compile the PLC station (Compile > Hardware (rebuild all)) and download to the controller. The connection resources are reserved at this point.

For S7-1200/1500, the equivalent setting is Properties > Protection & Security > Connection mechanisms > Permit access with PUT/GET communication from remote partner. Without this flag, an HMI connecting via S7 native (TCP/IP) is rejected even if the HMI connection is defined.

7. Network Configuration (PROFINET/MPI/PROFIBUS)

A correctly built HMI connection object still fails if the network layer is wrong. Validate the following parameters for every device in the project:

For PROFINET, the device name is the equivalent of an IP host name and is assigned via the PROFINET device name property. TIA Portal V13 supports PROFINET naming from the topology editor; if the HMI is on a different physical switch, the name must be assigned to the HMI's MAC address using Online & Diagnostics > Assign PROFINET device name. The exact procedure is in the Siemens PROFINET commissioning FAQ.

For PROFIBUS networks, the PROFIBUS address of the S7 CPU must match what the HMI connection references. If the PLC was migrated from MPI to PROFIBUS and the HMI connection still targets the MPI interface, TIA Portal will accept the configuration but the HMI will be unable to attach. Inspect Properties > PROFIBUS address > Address on both sides and ensure the HMI connection endpoint points at the PROFIBUS interface, not the PN interface.

8. HMI Tags and Connection Binding

Even with the HMI connection live, individual tags must be bound to a valid PLC address. TIA Portal V13 highlights invalid tag bindings in yellow at compile time.

• Open HMI_1 > HMI tags.
• Each tag with the Connection column set to Connection_1 will use the active HMI connection. Tags that are left at <Internal> do not leave the panel.
• Verify the PLC tag column references an existing DB or I/O address. A tag pointing at DB200.DBD0 on a CPU that has no DB200 generates a compilation warning, and the runtime falls back to the last known value or zero.
• For S7-1500, the optimized block access (symbolic-only) is the default. The HMI tag must use the symbolic name (e.g. "Data_block_1"."Motor_speed") and the connection must have Access mode > Symbolic access enabled. Absolute addressing is not permitted against optimized blocks.

Cross-reference the HMI tags with the loaded PLC program: Project tree > PLC_1 > Program blocks > right-click > Cross-references. Any HMI tag pointing at a non-existent address is listed as a warning in the inspector pane.

9. Compile, Download, and Commission

After the connection is created and the network is correct, follow this sequence to commission the new HMI:

1. Select the HMI in the project tree.
2. Click Compile > Software (rebuild all). Resolve all errors in the inspector window before proceeding.
3. Connect the PG/PC to the same PROFINET subnet as the HMI (or use the MPI/PROFIBUS cable).
4. Right-click the HMI → Download to device > Software and configuration.
5. In the Extended download to device dialog, select the correct network adapter, click Search, then highlight the HMI by its MAC or PROFINET name.
6. Click Load. Confirm any certificate prompts. The HMI restarts automatically when the download completes.
7. Open the panel's System > System information > Connections screen. The new HMI connection should display Status: Connected with the partner IP and connection type.

If the download fails with Download to device failed: HMI cannot be reached, check the PG/PC interface assignment in Set PG/PC interface (Start → SIMATIC → PC Internal). The wrong network adapter is the single most common cause of failed TIA Portal V13 downloads.

10. Diagnostics and Error Codes

When the HMI connection is live but tags do not update, the panel's alarm buffer contains the diagnostic event. TIA Portal V13 surfaces the following events for HMI-PLC connection faults:

For deeper diagnostics, use the Online & Diagnostics view on the PLC:

1. Mark PLC_1 in the project tree, click Go online.
2. Open Online & Diagnostics > Diagnostics > Connection. The list shows every active S7 connection partner with its TSAP and current state.
3. For PROFINET, switch to PROFINET diagnostics > Topology to confirm the panel is reachable on the wire.

On the HMI side, enable the system log to a USB stick for offline analysis. WinCC (TIA) stores SystemLog.csv in /home/industrial/Log on Comfort Panels and Basic Panels (PN). Open the file in Excel and filter for AlarmClass=Errors to find connection-related events.

11. Verification Checklist

Run through this checklist to confirm the second HMI is fully operational before handing the system back to production:

12. Migration Considerations for TIA Portal V13

Projects created in TIA Portal V13 cannot be opened in earlier TIA versions, but they can be migrated forward to V15, V16, or V17 without recompilation of the HMI connection. If a company-wide upgrade is in progress, follow this path:

1. Open the V13 project in TIA Portal V17 with the migration wizard.
2. Accept the prompt to upgrade the HMI connection. TIA Portal automatically maps legacy S7 connection (PROFINET) objects to the new format.
3. Recompile the project. Address any new warnings about deprecated connection modes.
4. Download the upgraded project to the HMI. The HMI runtime restarts with the new connection definitions.

Note that TIA Portal V13 SP1 reached end-of-life for product support in 2018, and V13 Update 9 (V13 SP2) extended support to 2020. For new installations, use TIA Portal V17 with the latest service packs. The HMI connection concepts described in this article remain valid across all TIA Portal versions from V13 through V19.

13. Frequently Asked Questions