Testing S7-1200 Programs Without a CPU: PLCSIM Setup Guide

Overview: The S7-1200 Offline Simulation Question

Engineers migrating from LOGO! to the SIMATIC S7-1200 frequently assume the new controller inherits the same offline simulation flow that LOGO! Soft Comfort provides. In practice, the S7-1200 followed a different roadmap. Siemens did not ship a dedicated S7-1200 simulator with TIA Portal V11, V12, or the original V13 release, which forced early adopters to debug against a real CPU on the bench using a starter kit or to borrow a CPU from a sister machine. With TIA Portal V13 SP1 (released March 2014) Siemens opened the door to S7-1200 simulation through S7-PLCSIM V13 SP1, and every TIA Portal release since — V14, V15, V15.1, V16, V17, V18, V19 — has retained and expanded that capability. This reference walks through the entire offline-simulation workflow: the firmware and TIA Portal version combinations that unlock PLCSIM for S7-1200, the exact project settings required to download to the virtual PLC, the verification instruments (watch tables, force tables, trace) available inside the simulated instance, and the limitations you must respect before treating the virtual CPU as a faithful stand-in for hardware. It also documents the starter-kit path for engineers who cannot yet run PLCSIM because of an older TIA Portal installation or because they need to validate firmware behaviour below V4.0.

Historical Context: Why S7-1200 Originally Lacked a Native Simulator

Three structural reasons delayed the appearance of a real S7-1200 simulator:

1. CPU-side simulation hooks. PLCSIM does not emulate the entire instruction set; it requires the active firmware to expose the standard test and commissioning interface defined by the S7-1200/S7-1500 system architecture. S7-1200 firmware prior to V4.0 (released 2013) implemented a subset of that interface. Full PLCSIM compatibility required the firmware rework that shipped as FW 4.0 (CPU 1211C/1212C/1214C) and FW 4.1/4.2 (CPU 1215C/1217C).
2. Catalog breadth. S7-300/400 PLCSIM could amortise its development cost across the entire 300/400 range. S7-1200 carries a longer tail of compact CPUs (1211C, 1212C, 1214C, 1215C, 1217C) and the F-variant safety controllers. Siemens chose to validate every CPU article before enabling simulation rather than ship a partial implementation.
3. Tool chain. S7-PLCSIM V5.x (STEP 7 V5.x) was a Win32 application tied to the older STEP 7 manager. The new simulator had to be a TIA Portal plug-in from day one, which pushed the delivery to the TIA Portal V13 timeframe.

Until that release, the only sanctioned path was a starter kit: a CPU bundled with a Basic Panel and a stripped-down TIA Portal that already contained the project's CPU article number. The catalog numbers from the Siemens product list remain valid for bench commissioning today:

These kits ship with the CPU, a Basic HMI panel (KTP400, KTP600, or KP300 depending on order), a power supply, Ethernet cable, and a 12-month TIA Portal licence. The CPU inside the kit is a fully functional 1212C or 1214C and can be used as a permanent bench controller once the development phase is over.

Prerequisites: Hardware, Software, and Firmware Requirements

To commission PLCSIM with an S7-1200 project, the following stack must align:

PLCSIM Version Compatibility Matrix for S7-1200

The following matrix reflects the S7-1200 simulation capability of every released PLCSIM build. Use it to choose the smallest TIA Portal version that still meets the project's CPU firmware.

Step-by-Step: Enabling PLCSIM for an S7-1200 Project

The following procedure uses TIA Portal V17 + PLCSIM V17 as the reference build. Earlier versions follow the same shape; later versions add a few extra wizards.

1. Create or open the project. In the project tree, double-click Add new device > SIMATIC PLC > S7-1200 CPU. Choose the article number that matches the real controller (for example 6ES7214-1BG40-0XB0 for CPU 1214C DC/DC/DC, FW 4.5).
2. Confirm the firmware. Select the CPU in the project tree, open Properties > System > Firmware version, and set the firmware to V4.5 (or whatever matches PLCSIM V17). If the dropdown is greyed out, the device was added from an older TIA Portal version and must be replaced with a current article.
3. Write or import the program. Open the Program blocks folder, add an OB1 (cyclic main) and the required FBs / FCs / DBs. Migration from LOGO! Soft Comfort can use the LOGO! to S7-1200 migration tool shipped as a TIA Portal add-in (Portal V16 or later).
4. Compile the program. Right-click the CPU → Compile > All (rebuild). Resolve every error before continuing; PLCSIM rejects a project with unresolved symbolic references.
5. Launch PLCSIM. Click Online > Simulation > Start (or press Ctrl+Shift+S). Portal starts the PLCSIM instance, which opens a virtual S7-1200 faceplate. The status indicator turns cyan when the simulated CPU is in RUN-capable state.
6. Download the project to the simulated CPU. Right-click the CPU → Download to device > All. PLCSIM uses the Softbus interface; no Ethernet configuration is required on the host PC. The download completes in 1–3 seconds for a typical project.
7. Switch the simulated CPU to RUN. Click the green play button on the PLCSIM faceplate, or use Online > CPU operating panel > Run (RUN-P). The status LED turns green; OB1 begins cyclic execution.
8. Open online diagnostics. Right-click the CPU → Go online > Online & diagnostics. The standard S7-1200 diagnostics buffer is fully available, with timestamped events identical to a real CPU.
9. Observe tags. Open a watch table, drag the relevant tags from the project tree, click Monitor all (glasses icon). Values update in real time as OB1 executes.
10. Force inputs/outputs. Right-click an input tag → Modify > Modify to 1. PLCSIM latches the forced value until released. Use this to drive the program through every branch without external wiring.
11. Stop and reset. Use Online > Simulation > Stop to terminate PLCSIM, or click MRES on the faceplate to wipe the simulated retentive memory.

Starter Kit Alternative: Real CPU on the Bench

When the project must stay on TIA Portal V11/V12, when the CPU firmware is intentionally pinned below V4.0 to validate field behaviour, or when PROFINET IO behaviour must be tested, a starter kit is the safer path. The kits below are still orderable and carry the original MLFB numbers.

The CPU inside the kit can be flashed with the latest S7-1200 firmware using the Siemens SIMATIC Automation Tool or the TIA Portal Online & diagnostics > Firmware update wizard. After flashing, the CPU behaves exactly like the production CPU, which means every migration step from LOGO! to S7-1200 can be exercised offline.

Supported Simulation Features and Known Limitations

PLCSIM replicates the S7-1200 user program faithfully but not the hardware interfaces. The following matrix summarises what works and what does not.

Programmatic Verification: Watch Tables, Force Tables, and Traces

PLCSIM does not limit the engineer to manual observation. The same verification instruments used on the real CPU are available against the virtual instance.

Watch table pattern

Open Watch and force tables > Add new watch table. Configure the following columns for a clean diagnostic workflow:

Name           | Address    | Display format | Modify value
"Start PB"      | %I0.0      | BOOL           | 1
"Run motor"     | %Q0.0      | BOOL           | —
"Speed set"     | %MW10      | DEC+-          | 1500
"Actual speed"  | %MW12      | DEC+-          | —
"Fault"         | %MW20      | HEX            | —

Tick Monitor all to refresh every 200 ms, or use Monitor (slow) for one update per cycle. The simulated values change exactly as they would on a wired CPU.

Force table pattern

For repeatable test cases, use a force table. PLCSIM supports up to 30 forced tags simultaneously. Mark the Force column to latch a value across OB cycles, including across simulated CPU STOP-RUN transitions. Use this to lock motor-enable lines while testing interlocks, or to fix a sensor input while exercising a counting sequence.

Trace viewer

TIA Portal V15+ ships a function trace that records OB1 signals, OB35 interrupt signals, and any tag you select. Inside PLCSIM, recordings proceed normally and can be exported as .csv for offline analysis. Typical sample rates:

• OB1 trace: 10 ms
• OB35 trace: 1 ms (configurable to 0.5 ms)
• High-speed trace (PLCSIM V17+): 0.1 ms (API-driven)

PLCSIM API for automation

For headless testing, drive PLCSIM from a .NET application using the Siemens SIMATIC S7-PLCSIM API. Minimal C# sample to set input I0.0 to TRUE for 100 ms:

var plc = new PlcInstance("S7-1200");
plc.Connect();
plc.WriteBool("I0.0", true);
System.Threading.Thread.Sleep(100);
plc.WriteBool("I0.0", false);
plc.Disconnect();

This API is documented in the SIMATIC S7-PLCSIM V17 Function Manual on the Siemens support portal.

Commissioning Workflow: From Simulation to Real CPU

PLCSIM catches the majority of program bugs before they reach hardware. The recommended handover sequence is:

1. Unit test in PLCSIM. Run the entire program with simulated inputs. Document every input vector and expected output.
2. Static analysis. Run Program > Compile > Consistency check. Resolve every warning before continuing.
3. HMI test in PLCSIM. If the project includes a KTP400/KTP600/Comfort Panel, start the HMI runtime against PLCSIM via WinCC > Start runtime. Validate screens, alarms, and tag connections.
4. Hardware FAT. Power the real CPU on the bench, set its IP to match the project, download the program, run the same input vectors, compare outputs to the PLCSIM run.
5. On-site SAT. With real wiring connected, run the same vectors one more time. Only changes from the FAT log should be mechanical/electrical, not software.

Troubleshooting Matrix

FAQ