1. Overview: Why a Laptop as a Siemens PLC?
Engineers frequently need to validate S7-300 and S7-400 control logic, HMI screens, and Profibus I/O behavior long before the real automation hardware is delivered. Two Siemens software paths exist for using a Windows host as the controller: PLCSIM (a pure simulator that runs inside STEP 7) and WinAC RTX (a real-time soft-PLC that behaves like a real S7-CPU on the host machine). The two products are not interchangeable, and the choice determines which Profibus hardware you may attach, which engineering workflows are valid, and whether the laptop can be used in a production-relevant test bench.
This reference consolidates the engineering constraints, the supported CP (Communications Processor) cards, the Windows platform requirements, and the realistic alternatives (Microbox 427C, Nanobox PC, embedded controllers) for S7-300/400 development on a mobile host. It is written for engineers using STEP 7 V5.4/V5.5 with Graph and SCL, who also need to run WinCC and integrate third-party Profibus DP slaves.
2. Prerequisites
| Item | Requirement |
|---|---|
| STEP 7 | V5.4 SP3 or V5.5 (Graph, SCL, optional CFC) |
| Operating system | Windows XP Professional SP3 (32-bit) for legacy WinAC RTX 2010; Windows 7 / 10 64-bit for newer S7-PLCSIM in TIA Portal |
| Engineering host | Dell Vostro 3700 (Core i3/i5, 4 GB RAM) or equivalent with at least one free PCIe slot for a Profibus CP |
| Profibus hardware | CP 5611 (PCI), CP 5613 (PCI), CP 5614 (PCIe), CP 5621 (PCIe) – not CP 5512 (PCMCIA) and not USB PC Adapter (CP 5711) when using WinAC RTX |
| Real-time extension | Ardence/RTX 2010 runtime (bundled with WinAC RTX) for hard real-time behavior |
| HMI software | WinCC flexible 2008 SP3 or WinCC V7 for HMI download and runtime |
3. PLCSIM vs. WinAC RTX: Functional and Architectural Differences
The most common confusion is to treat PLCSIM as a lighter version of WinAC RTX. Architecturally they are completely different products and the differences are not negotiable.
3.1 PLCSIM (S7-PLCSIM in STEP 7 V5.x)
- Pure simulator integrated into STEP 7; no real-time OS extension required.
- Emulates an S7-300 or S7-400 CPU in a virtualized address space; the simulated CPU exchanges I/O with internal memory only.
- Communication with STEP 7, WinCC, and OPC servers is performed over the internal SoftBus (a virtual MPI/PROFIBUS interface mapped to TCP/IP via the
PLCSIM.S7ONLINEaccess point). - No real Profibus DP master, no real I/O modules, no third-party Profibus slaves. CP 5512, CP 5611, CP 5621, and the USB PC Adapter are visible to the operating system but PLCSIM will not use them to exchange process data.
- Lifecycle: license tied to the STEP 7 installation; PLCSIM instance is started from the SIMATIC Manager.
3.2 WinAC RTX (Windows Automation Center – Real-Time eXtension)
- Real-time soft PLC based on the Ardence (now IntervalZero) RTX real-time extension to the Windows kernel.
- Runs as a Windows service (
S7RTM) with deterministic cycle times (typical 1 ms OB1 tick, with background tasks on the RTX subsystem). - Acts as a real S7-CPU and is programmed with STEP 7 in the same way as a 315-2 DP or 416-3 PN/DP. Hardware configuration (HW Config) is performed with a soft-PLC CPU type, e.g.
WinAC RTX 2010(6ES7 671-0RC08-0YA0 catalog number). - Supports a real Profibus DP master interface, but only via specific CPs. See the Siemens Industry Online Support entry for the WinAC RTX 2010 manual (search term WinAC RTX 2010 Getting Started) for the current list of supported CPs.
- Can host a WinCC flexible Runtime or WinCC Runtime Professional that communicates over the SoftBus or over a TCP/IP S7 connection.
3.3 Side-by-side comparison
| Feature | PLCSIM V5.4 | WinAC RTX 2010 |
|---|---|---|
| Real-time behavior | No (host Windows scheduler) | Yes (RTX subsystem, sub-millisecond jitter) |
| Real Profibus DP master | No | Yes (selected CPs only) |
| Third-party Profibus DP slaves | No | Yes (GSD import required) |
| CP 5512 (PCMCIA) | Used for STEP 7 online only | Not supported as DP master |
| CP 5611 / CP 5613 / CP 5614 / CP 5621 | Used for STEP 7 online only | Supported as DP master |
| USB PC Adapter (CP 5711) | Used for STEP 7 online only | Not supported as DP master |
| WinCC runtime | Yes (via SoftBus) | Yes (via SoftBus or S7 TCP/IP) |
| Standby / hibernation | Allowed | Disabled by the rtxobj driver |
| Use in production | No | Permitted by Siemens for non-safety control; not for mobile/laptop use |
4. Profibus CP Cards: Which One to Use
For a laptop-based test bench using WinAC RTX, the only viable Profibus DP master CPs are PCI or PCIe cards. Modern laptops with ExpressCard slots can host PCIe CPs through an ExpressCard-to-PCIe adapter, although Siemens has qualified only a limited set of chassis (see the WinAC RTX release notes).
| Catalog Number | Form Factor | Bus Type | Use with WinAC RTX | Use with PLCSIM |
|---|---|---|---|---|
| 6GK7 551-2AA00 | PCMCIA Type II | PCMCIA (CardBus) | No | STEP 7 online only |
| 6GK7 561-1AA00 (CP 5611) | PCI short card | PCI 32-bit | Yes | STEP 7 online only |
| 6GK7 561-3AA01 (CP 5613) | PCI short card | PCI 32-bit | Yes (A1/A2) | STEP 7 online only |
| 6GK7 561-4AA00 (CP 5614) | PCIe x1 | PCIe | Yes | STEP 7 online only |
| 6GK7 562-1AA00 (CP 5621) | PCIe x1 | PCIe | Yes | STEP 7 online only |
| 6GK1 571-1AA00 (CP 5711) | USB | USB 2.0 | No | STEP 7 online only |
For a Dell Vostro 3700 (no PCMCIA, no ExpressCard, no internal PCIe slot), the situation is particularly restrictive: there is no way to install a CP 5611/5613/5614/5621 directly. The only options are:
- Use PLCSIM (no real Profibus) and validate only the control logic, then validate Profibus DP at the final FAT/SAT with the real PLC.
- Use a USB-to-Profibus converter from a third party (Hilscher, Helmholz, Molex/Woodhead) and treat the laptop strictly as an engineering host, not as a WinAC RTX DP master.
- Move the WinAC RTX instance to an industrial PC or embedded platform that has a PCIe slot (see section 6).
5. Software Installation Order on a Laptop
The installation order matters; otherwise the SoftBus and the PC internal access point will be misconfigured.
- Install the operating system. Windows XP Professional SP3 is supported by WinAC RTX 2010; Windows 7 Professional 32-bit is supported by the SP3 update. Windows 10/11 are not officially supported by WinAC RTX 2010.
- Install STEP 7 V5.4 SP3 or V5.5 SP3 (including Graph and SCL if used).
- Install any CP drivers (CP 5512, CP 5611, CP 5621) so that the PG/PC interface dialog shows the CP in addition to the PC internal access point.
- Install PLCSIM from the STEP 7 setup (component "S7-PLCSIM").
- Install Ardence RTX 2010 (this is installed as a prerequisite of WinAC RTX).
- Install WinAC RTX 2010. The setup registers the
WinAC RTXentry in HW Config and theRTXaccess point in Set PG/PC Interface. - Install WinCC flexible 2008 SP3 Runtime or WinCC V7 Runtime, depending on the project type.
- Reboot. The RTX subsystem extends the Windows boot sequence. After the reboot, the Set PG/PC Interface dialog must show a
RTXentry; if not, the RTX driver is not loaded.
6. Alternative Mobile Hosts: Microbox, Embedded Controller, Nanobox
For a portable test bench that needs real Profibus I/O, Siemens' own product line of industrial PCs is the supported approach. The following catalog numbers are representative and were current at the time of writing. Always verify availability and the current WinAC RTX 2010 release notes on the Siemens Industry Online Support portal (search term WinAC RTX release notes).
| Device | Catalog Number (typical) | Profibus Slot | Notes |
|---|---|---|---|
| Microbox 427C | 6AG4 100-0BA10-0FX0 | 1 × PCIe x1 | Compact, 24 V DC, no fan in some SKUs; supports CP 5614 / CP 5621 |
| Embedded Controller EC31 | 6AG3 121-2AC00 | 1 × PCIe x1 | DIN-rail mount, no moving parts |
| Nanobox PC | 6AG4 060-0A... | Mini-PCIe / mPCIe | Use CP 5623 (mPCIe) – verify release notes |
| Panel PC 477B | 6AV7 814-... | PCI / PCIe | The reference platform mentioned in the field report |
| PC/104 + extension box | 3rd party | PC/104 + CP 5613 | For an embedded stack with one CP 5613 per Profibus segment |
All of the above support WinAC RTX 2010. None of them support a mobile sleep/standby transition. The mobile host is "mobile" only in the sense of a briefcase-size device with a 24 V DC input and a detachable CFast or SSD drive, not in the consumer-laptop sense.
7. Configuring PLCSIM for an S7-300/400 Project
- Open SIMATIC Manager and open the S7 project.
- In HW Config, right-click the CPU (e.g., CPU 315-2 DP, 6ES7 315-2AG10-0AB0) and select Object Properties → Target System. Change the target from the real CPU to PLCSIM. Save and compile the hardware (Station → Save and Compile).
- Open Set PG/PC Interface (Control Panel → SIMATIC). Set the access point
S7ONLINEtoPLCSIM.S7ONLINE. - Start the PLCSIM application. A virtual CPU window appears with status indicators for RUN/STOP, INTF, BUZ, and force tables.
- Download the hardware configuration and the S7 program blocks to the PLCSIM instance (target system = PLCSIM).
- Click the green RUN toggle in PLCSIM. The simulated CPU executes OB1 with the configured cycle time. Use PLCSIM's I/O checkboxes to drive inputs and observe outputs in VAT (Variable Table) or in a connected WinCC runtime.
8. Configuring WinAC RTX for an S7-300/400 Project
- Open the WinAC RTX Console from the Start menu (Siemens SIMATIC → WinAC RTX). The console shows the state of the S7RTM service, the RTX subsystem, and the assigned Profibus CPs.
- Confirm the S7RTM service status is Running. If not, click Start. The service is a Windows service; once running it survives logon transitions.
- Open SIMATIC Manager. In HW Config, insert a WinAC RTX station (e.g., WinAC RTX 2010, 6ES7 671-0RC08-0YA0) and configure the slots. Add the Profibus CP (CP 5613 / CP 5614 / CP 5621) to the appropriate PCI device index. Configure the DP master and import the GSD files of any third-party Profibus slaves.
- Compile and download the hardware configuration to the WinAC RTX station. Use the Target system → Download menu, with Set PG/PC Interface pointing to
RTX(or the specific CP entry under RTX). - Download the S7 program (blocks, system data, SDBs).
- Switch the WinAC RTX station to RUN from the console or from SIMATIC Manager. The CPU begins cycling OB1 against the real Profibus DP network.
9. Profibus DP Master Commissioning with WinAC RTX
For a test bench with one CP 5613 / CP 5614 / CP 5621 acting as a DP master and a set of third-party slaves:
- Import the GSD file of each slave via Options → Install GSD File in HW Config.
- Drag the slave from the hardware catalog onto the DP master line. Assign a unique Profibus address (1–125) and configure the I/O slot mapping.
- Verify the bus topology: terminators on both ends, bus cable shield grounded at each cabinet entry, baud rate consistent with the longest segment (12 Mbit/s only on very short segments with ET 200S; 1.5 Mbit/s is the typical safe default for 100 m of cable).
- Use a Profibus diagnostics tool (e.g., the Siemens BT 200 or the Softing PB-QPS) to verify the signal quality. Aim for > 70 % eye opening on the oscilloscope for new installations.
- Power on the slaves and download the WinAC RTX project. The S7RTM console will report the DP slaves that come online; failures are reported as diagnostic interrupts (OB82) with the slave's diagnostic buffer text.
10. WinCC Runtime Integration
WinCC and PLCSIM/WinAC RTX use different access points:
-
PLCSIM: WinCC uses the connection SIMATIC S7 Protocol Suite → TCP/IP →
PLCSIM.S7ONLINE. The PLC is reachable at the loopback address127.0.0.1with rack 0 and slot 2 (or whatever the simulated CPU's logical address is). This works without a CP. - WinAC RTX: WinCC can use either the SoftBus (a virtual MPI/Profibus connection) or a native TCP/IP S7 connection via the standard SIMATIC S7 Protocol Suite. The S7 connection must use the WinAC RTX's logical address (rack 0, slot of the CPU entry in HW Config, typically slot 3 for a WinAC RTX station). Routing through CP 5621 is not a typical WinCC path; WinCC always talks to the CPU, not to the CP.
11. Verification and Acceptance Checklist
| Check | Expected Result | How to Verify |
|---|---|---|
| STEP 7 online to PLCSIM | CPU in RUN, scan monitor shows OB1 executing | SIMATIC Manager → PLC → Monitor/Modify |
| STEP 7 online to WinAC RTX | CPU in RUN, RTM console shows green status | WinAC RTX Console → Status tab; cross-check in SIMATIC Manager |
| Profibus slaves online | All slaves reachable, no diagnostic interrupts | CPU diagnostic buffer empty; CP 5613/5614/5621 LED on port is solid green |
| WinCC connection | All configured tags show current values | WinCC Tag Manager → diagnosis; the connection status icon is green |
| OB1 cycle time | Within project specification (e.g., < 50 ms) | Monitor OB1 runtime in the CPU's module information |
| Force table behavior | PLCSIM force works; WinAC force limited to test mode | PLCSIM: checkbox toggles bits. WinAC: forces only with safety acknowledgment |
| Standby / hibernation | System never enters standby | Power Options → Sleep: Never; Hybrid Sleep: Off |
12. Troubleshooting Matrix
| Symptom | Likely Cause | Resolution |
|---|---|---|
| STEP 7 cannot reach the laptop CPU | PG/PC interface set to the wrong CP entry | Open Set PG/PC Interface, choose PLCSIM.S7ONLINE for PLCSIM or RTX for WinAC RTX |
| "Cannot find CP 5613" error in HW Config under WinAC RTX | CP driver not installed, or card in a slot the BIOS does not enumerate | Reinstall the SIMATIC NET PC software; verify the card in Device Manager; try a different slot |
| DP slave shows bus fault, diagnostic buffer says "station failure" | Wrong Profibus address, missing terminator, or baud rate mismatch | Verify the slave's DIP switch / rotary address, check both ends of the segment for terminators, lower the baud rate to 1.5 Mbit/s |
| WinAC RTX station is in STOP with OB86 "DP master failure" | CP not assigned, or CP driver disabled in RTX | Open the WinAC RTX console → Profibus tab; verify the CP is Active |
| System enters standby during a test | RTX driver is loaded but Windows power policy is still aggressive | Disable Sleep, Hybrid Sleep, and USB selective suspend in Power Options |
| PLCSIM runs, but WinCC tags stay # | Wrong rack/slot in the WinCC connection | In WinCC Channel Diagnosis, set rack = 0, slot = 2 (PLCSIM default) or the slot of the WinAC RTX CPU |
| CP 5711 (USB) recognized by STEP 7 but ignored by WinAC RTX | By design – CP 5711 is not a supported DP master for WinAC RTX | Replace with CP 5613/5614/5621, or move the WinAC instance to a PC with a PCIe slot |
| CP 5512 visible but not selectable as DP master in HW Config | By design – PCMCIA form factor is not supported as a DP master for WinAC RTX | Use a PCI/PCIe CP, or use PLCSIM for logic-only testing |
| Graph / SCL blocks fail to download to WinAC RTX | STEP 7 / WinAC version mismatch | Use the WinAC RTX compatibility tool from the Siemens Industry Online Support portal to match STEP 7 SP and WinAC RTX SP |
13. Frequently Asked Questions
What is the difference between PLCSIM and WinAC RTX?
PLCSIM is a software-only simulator that runs inside STEP 7 V5.x and exchanges I/O with internal memory over the SoftBus; it has no real Profibus DP master and supports no real I/O. WinAC RTX is a real-time soft PLC that runs on top of the RTX real-time extension to Windows, behaves like a real S7-CPU, and can act as a real DP master via supported CP cards (CP 5611 / 5613 / 5614 / 5621). PLCSIM is for logic validation; WinAC RTX is for realistic test benches and for use as a production controller on a Siemens-qualified industrial PC.
Can I attach a real Profibus DP slave to PLCSIM?
No. PLCSIM is a pure simulator; it does not drive the Profibus line. Real DP slaves can only be attached to WinAC RTX (or to a real S7-CPU). The CP 5512, CP 5611, CP 5621, and CP 5711 are visible to STEP 7 for online commissioning when using PLCSIM, but they are not used for I/O exchange.
Why does the USB PC Adapter (CP 5711) not work with WinAC RTX?
WinAC RTX requires a PCI or PCIe Profibus CP that the RTX real-time subsystem can drive deterministically. The CP 5711 is a USB device intended for STEP 7 online PG functions, not a DP master for a real-time soft PLC. Use CP 5613 (PCI), CP 5614 (PCIe), or CP 5621 (PCIe) for WinAC RTX Profibus master applications.
Why does the CP 5512 (PCMCIA) not work with WinAC RTX?
The PCMCIA/CardBus bus is not in the WinAC RTX support matrix. The CP 5512 is qualified for STEP 7 online programming only. For WinAC RTX, install a CP 5611, 5613, 5614, or 5621 in a PCI/PCIe slot, or move the soft-PLC instance to a Microbox 427C / embedded controller that has a suitable slot.
Is a laptop a supported host for WinAC RTX?
No. Siemens explicitly states that WinAC RTX is not intended for mobile use on a consumer laptop. The RTX driver disables standby and hibernation, the Profibus CPs are PCI/PCIe devices that most laptops cannot host, and the WinAC RTX release notes restrict supported platforms to Siemens industrial PCs (Microbox 427C, Nanobox PC, Panel PC 477B, etc.). For laptop-only development, use PLCSIM for logic validation, and validate Profibus and HMI behavior on a Siemens-qualified industrial PC before factory acceptance.
Can I run WinCC on the same laptop that runs PLCSIM or WinAC RTX?
Yes. For PLCSIM, point the WinCC S7 channel at the PLCSIM.S7ONLINE access point on the loopback address 127.0.0.1. For WinAC RTX, the WinCC S7 channel uses the standard TCP/IP S7 connection to the WinAC RTX CPU's logical address (rack 0 and the configured slot of the CPU). Use the WinCC Channel Diagnosis tool to verify tag values during commissioning.