S7-PLCSIM V13 S7-300 Simulation Errors: Root Cause and Fix

When engineers attempt to simulate legacy SIMATIC S7-300 or S7-400 controllers inside TIA Portal V13 using S7-PLCSIM V13, the simulator either refuses to load the project, drops the connection, or returns a "target PLC differs from online project" alarm. The root cause is a hard compatibility boundary between the PLCSIM V13 runtime and the S7-300/400 instruction set, not a project download error or a network mismatch. This reference walks through the exact failure modes, the firmware-level reason they occur, and the field-proven workarounds that restore simulation in TIA V13, TIA V13 SP1, and TIA V13 SP2 environments.

1. Problem Description

Engineers upgrading from classic STEP 7 V5.x to TIA Portal V13 typically install the latest PLCSIM available in the TIA media package. They then open an existing S7-300 program (originally created in STEP 7 V5.5 or migrated to TIA) and try to Start simulation. The following symptoms are reported in the field:

• Symptom A — Silent refusal to start: After pressing "Start simulation" with the S7-300 CPU selected, the PLCSIM V13 instance spins up but the project does not download. TIA displays "The target PLC_1 in the offline project is different from the target in the online project (address 192.168.0.1)" or "The target CP1 PLC in the offline project is different from the target in the online project (address 2)".
• Symptom B — No valid target type: The S7-300 CPU type does not appear in the PLCSIM V13 "Add new device" catalog. Only S7-1200 and S7-1500 controllers are listed.
• Symptom C — Project download fails with online/offline mismatch: The online accessible nodes window shows a PLCSIM instance, but the CPU slot, IP address, or rack configuration does not match the offline project, producing an online/offline difference alarm that cannot be acknowledged.
• Symptom D — Mixed-stack simulation attempts fail: Engineers trying to simulate an S7-300 station with S7-PLCSIM V13 receive inconsistent behavior depending on whether the project was migrated from STEP 7 V5.5 or rebuilt from scratch inside TIA Portal V13.

The most common alarm in the engineering logs reads exactly:

A second variant on PROFIBUS CP modules reads:

2. Root Cause

S7-PLCSIM V13 is engineered exclusively for the SIMATIC S7-1200 and S7-1500 controller families. It does not contain the S7-300/S7-400 instruction set, the MPI/PROFIBUS slot model, or the legacy MLFB catalog required to emulate those CPUs. The mismatch error that surfaces during Go online is a downstream symptom of the simulator rejecting the S7-300 station at load time.

There are two distinct error categories that the engineer must understand:

2.1 Project-Level Rejection (the "different target" alarm)

TIA Portal V13 enforces a strict check between the offline project configuration and the online target it tries to reach. When S7-PLCSIM V13 cannot host the S7-300 CPU, it boots a default PLCSIM instance with a default IP (commonly 192.168.0.1) and a placeholder S7-1500/ET200SP slot model. The offline project — which still references, for example, a CPU 315-2 PN/DP at 192.168.0.10 — therefore disagrees with the online device on three parameters simultaneously:

The error message text wraps the address field to the actual mismatch value: an IP address of 192.168.0.1 indicates an IP mismatch, while address 2 typically references a PROFIBUS DP slave address or a slot index disagreement between the offline configuration and the PLCSIM placeholder.

2.2 MLFB Incompatibility (the "PLCSIM has its own MLFB" notice)

Even when PLCSIM V13 successfully emulates an S7-1200 or S7-1500 target, the simulator exposes a synthetic MLFB such as 6ES7 5XX-... that does not match the real CPU's MLFB in the project. TIA Portal raises a warning to this effect. For S7-1200/S7-1500 simulation this warning can be safely ignored — it is informational, not an error. The CPU still executes OB1, OB35, OB82, and the user program as if it were a physical controller.

For S7-300/S7-400, the same warning also fires, but the underlying instruction set is not loaded, so OB1 never executes and outputs remain frozen at their default values. Suppressing the warning does not recover the simulation.

3. Compatibility Matrix

4. Solution Paths

Three field-proven solutions exist. The correct choice depends on project lifetime, hardware target, and the version of STEP 7 already deployed on the engineering workstation.

4.1 Solution A — Use S7-PLCSIM V5.x (Recommended for legacy S7-300/400 projects)

When TIA Portal V13 Professional is installed, the installation media includes both the new PLCSIM V13 and the legacy PLCSIM V5.x for S7-300/S7-400. The two simulators coexist on the same workstation and are launched from different entry points.

1. Open Control Panel → Programs and Features and verify that SIMATIC STEP 7 PLCSIM V5.x is installed alongside TIA Portal V13.
2. If the entry is missing, run the TIA V13 Professional setup and select SIMATIC STEP 7 (TIA Portal) → PLCSIM V5.x for S7-300/400 as an additional package.
3. Open the S7-300 project in the TIA Portal V13 project tree.
4. Right-click the S7-300 station → Start simulation. TIA will detect the S7-300 CPU and route the launch to PLCSIM V5.x instead of PLCSIM V13.
5. PLCSIM V5.x opens in its classic window. Click RUN-P to start cyclic execution.
6. Press Go online in TIA Portal V13. The "target differs from online" alarm should not appear because PLCSIM V5.x advertises the correct S7-300 MLFB and slot model.

4.2 Solution B — Continue with Classic STEP 7 V5.5 (Recommended for non-migrated S7-300/400 fleets)

If the S7-300 program was not migrated into the TIA project tree and remains a .s7p project, the most stable simulation environment is still STEP 7 V5.5 + PLCSIM V5.4. The mismatch error does not occur in this toolchain.

1. Open the project in SIMATIC Manager (STEP 7 V5.5).
2. Select the S7-300 station → Options → Module Information to confirm the CPU MLFB.
3. Launch S7-PLCSIM V5.4 from the Windows Start menu.
4. Download the station to PLCSIM via PLC → Download.
5. Toggle PLCSIM to RUN-P. OB1 will execute.

4.3 Solution C — Migrate the Application to S7-1500 (Recommended for new development)

For new machines or for engineers standardizing on TIA Portal V13+, the long-term solution is to migrate the S7-300 program to a S7-1500 CPU (for example, a CPU 1511-1 PN or CPU 1515-2 PN) and simulate with PLCSIM V13. Siemens provides a migration toolchain that translates STEP 7 V5.5 S7-300 projects into TIA Portal S7-1500 projects. After migration:

1. Open the migrated project in TIA Portal V13 SP2.
2. Select the S7-1500 station → Start simulation. PLCSIM V13 launches as a fully functional S7-1500 emulator.
3. Press Go online. The IP mismatch alarm does not occur because the PLCSIM V13 instance advertises the same S7-1500 MLFB defined in the project.

5. Step-by-Step: Resolving the "Different Target" Alarm in TIA V13

Use this procedure when the alarm fires but you are unsure whether the project is genuinely misconfigured or whether PLCSIM is the wrong tool.

1. Confirm the CPU family in the project. In the TIA project tree, expand Devices & Networks and inspect the station icon. S7-300 stations show a 300-series icon; S7-1200/1500 show the newer iconography.
2. Open the device configuration. Note the MLFB (e.g., 6ES7 315-2EH14-0AB0) and the IP address assigned to the PROFINET interface.
3. From the TIA Portal menu, choose Online → Accessible nodes. If a node appears at 192.168.0.1 with an S7-1500 MLFB, PLCSIM V13 has launched but is hosting the wrong family — go to step 4. If no node appears, PLCSIM never started — re-trigger Start simulation with administrator rights.
4. Close PLCSIM V13. Switch to the S7-300-compatible simulator (PLCSIM V5.x) by following Solution A above.
5. Re-attempt Go online. The alarm should clear.

6. Why the PLCSIM V13 MLFB Warning Is Safe to Ignore (For S7-1200/1500)

When simulating an S7-1200 or S7-1500 with PLCSIM V13, the project configuration references the real CPU's MLFB (for example, 6ES7 511-1AK02-0AB0), but the running PLCSIM instance reports its own synthetic MLFB. TIA Portal raises the "target differs" notice in this case as well. This is expected behavior:

• The PLCSIM V13 instance is functionally equivalent to a physical S7-1500 with the same firmware version.
• OB1, OB35, OB82, OB121, motion control OBs, and the user program execute against the simulated process image.
• Watch tables, force tables, and trace functionality operate as on real hardware.

Click OK on the warning and proceed. Do not attempt to "correct" the MLFB — there is no field to change it.

7. Verification Checklist

Use this checklist to confirm that the simulation is fully operational after applying one of the three solutions above.

8. Troubleshooting Matrix

9. Field-Proven Caveats

• PLCSIM V5.x and PLCSIM V13 cannot run the same S7-300 station simultaneously. Close one before opening the other to avoid TCP port conflicts on the PLCSIM loopback interface (default 192.168.0.1).
• The S7-PLCSIM V13 SP2 trial referenced in the Siemens support entry ID 109745155 is intended for evaluation only. Production environments require a valid license.
• Migrated S7-300 projects sometimes carry hidden PROFIBUS DP master configurations that PLCSIM V13 cannot emulate. Remove or disable PROFIBUS master interfaces before attempting S7-1500 simulation of a migrated program.
• F-CPU safety simulation is not supported in any PLCSIM version. Fail-safe S7-300F and S7-1500F programs must be validated on physical F-CPUs with F-I/O.
• S7-PLCSIM V13 SP2 introduced explicit Windows 10 support. Earlier SPs (V13 base, V13 SP1) install on Windows 10 only with manual compatibility shims.

10. Decision Flowchart

The following decision tree summarizes the correct simulator choice for a given project:

1. Is the target PLC an S7-1200 or S7-1500? → Use S7-PLCSIM V13 (SP1 or SP2).
2. Is the target PLC an S7-300 or S7-400? → Use S7-PLCSIM V5.4/V5.5 with STEP 7 V5.5 or TIA Portal V13 Professional.
3. Is the project still under active S7-300 development with no migration plan? → Stay on STEP 7 V5.5 + PLCSIM V5.x for stability.
4. Is the project a new development or scheduled for migration? → Migrate to S7-1500 + PLCSIM V13 SP2 for long-term support.

11. Summary

The "target PLC differs from online project" error in TIA Portal V13 with an S7-300 station is a simulator compatibility symptom, not a project configuration defect. S7-PLCSIM V13 (base, SP1, and SP2) does not contain the S7-300/S7-400 instruction set and cannot host those CPUs. The correct resolution is to use S7-PLCSIM V5.x, which is bundled with TIA Portal V13 Professional and supports the legacy S7-300/S7-400 families natively. For long-term fleets, plan a migration path to S7-1500 to take advantage of PLCSIM V13's modern emulation features, including trace, Web server simulation, and OPC UA server emulation. The SP2 release of PLCSIM V13, documented in Siemens support entry ID 109745155, added Windows 10 support and should be the preferred PLCSIM V13 baseline for new installations.

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