Configuring Windows XP VMware VM for Siemens STEP 5 DOS

Overview: Why STEP 5 Requires a DOS or Windows XP Runtime

Siemens STEP 5 is the classic ladder logic and statement list programming environment for the SIMATIC S5 PLC family (S5-90U, S5-95U, S5-100U, S5-115U, S5-135U, S5-155U). The original programming package was distributed as a 16-bit DOS executable set (S5-DOS, order number 6ES5 848-7CA00) with a Windows 3.1/3.11 front-end shell. Later releases (STEP 5 V6.6 and the optional ProTool/ProAgent add-on) target Windows 95, 98, NT 4.0, and Windows XP SP3 but still launch the core S5 components from a DOS command window that is not resizable and that returns to a fixed 80x25 character cell when maximized.

This behavior is by design: the S5 programming kernel uses direct DOS interrupts (INT 21h, INT 10h) and direct parallel-port I/O for the AS511 serial converter. Modern 64-bit Windows releases block those paths, and Windows Vista and later remove the NTVDM subsystem entirely. A virtualized Windows XP (or pure DOS) guest is the only supported way to run STEP 5 on current hardware, and VMware Workstation / Player / Fusion are the most common hypervisors in automation shops because they keep the host fully isolated from the legacy OS.

Prerequisites

Choosing the VMware Edition

Broadcom currently distributes three VMware products relevant to legacy automation workloads. Pick by use case, not by feature count.

Apple Silicon (M1/M2/M3) Macs cannot run x86 Windows XP guests natively in Fusion 13.5; use an Intel Mac or a Windows host. The community-published VMware Workstation 17.6.4 Windows XP guest reference documents the exact settings matrix used here and is a useful companion document for the install sequence below.

Host Hardware Virtualization Configuration

VMware Workstation and Player require hardware-assisted virtualization to be exposed by the host firmware. Confirm before installing the hypervisor.

1. Reboot the host and enter BIOS/UEFI setup (Del, F2, or F10 depending on vendor).
2. Locate Intel VT-x or AMD-V and set to Enabled.
3. On Intel systems, also enable VT-d (directed I/O) if you plan to use a physical USB programming cable passed through.
4. Disable Hyper-V, Windows Hypervisor Platform, Windows Sandbox, Credential Guard, and Core Isolation on Windows 11 hosts. These Windows hypervisors claim VT-x exclusively and prevent VMware from starting virtual machines.
5. Boot the host and verify with the VMware vmware-checkvm command (Workstation Pro) or the Player About dialog. Both must report Virtualization enabled.

Creating the Windows XP Guest

Use a fresh, pre-allocated NTFS virtual disk. Thin provisioning combined with Windows XP's lack of TRIM awareness can cause the .vmdk to fragment badly over time.

1. Open VMware Workstation Pro 17.6.4 and choose File → New Virtual Machine → Custom (advanced).
2. Select Installer disc image file (ISO) and point to your Windows XP SP3 ISO. If you have the original CD, select Installer disc instead.
3. Set Guest OS to Microsoft Windows and Version to Windows XP Professional. VMware does not list XP in Workstation 17; pick Windows XP Professional (32-bit) from the legacy list or use Windows 2000 as a fallback (the kernel and HAL differ but the S5W installer runs identically).
4. Allocate 1 GB RAM (the XP kernel will not see more than 4 GB regardless).
5. Set processors to 1 and cores per processor to 1. XP is not SMP-aware; assigning multiple cores triggers the XP HAL to spin on missing APIC vectors.
6. Set the network adapter to Host-only (VMnet1). Bridged networking exposes the legacy OS to the production LAN and is a security risk.
7. Create a new virtual disk: SCSI or IDE, capacity 20 GB, Allocate all disk space now, Store virtual disk as a single file.
8. Finish the wizard, then edit the VMX file and append:
   
   monitor_control.restrict_backdoor = "TRUE"
monitor_control.enable_svm = "TRUE"
svga.vramSize = "16777216"
   These stop the VMware tools backdoor driver from interfering with the AS511 COM-port handshake.

Power on the VM. Press F2 inside the BIOS screen of the VM (the VM has its own 2-second boot menu) and set the CD-ROM as the first boot device. Run a normal XP setup, then install VMware Tools 11.3.5 (the last build with XP guest support) from VM → Install VMware Tools.

Importing an Existing Physical XP Installation

If your maintenance bench still has a physical Windows XP workstation with a licensed STEP 5 install and a calibrated PC adapter (e.g. 6ES5 734-1BD20), the disk-to-VMDK conversion preserves licensing and custom symbol libraries. The most reliable conversion path is:

1. Use disk2vhd (Sysinternals) on the physical XP host to create a VHDX image of the system partition. Power down the XP host first; online VSS is unreliable on XP.
2. Copy the VHDX to the VMware host and convert it to VMDK with qemu-img convert -f vhdx -O vmdk -o adapter_type=ide source.vhdx target.vmdk.
3. Create a new VM in Workstation as in the previous section, but select Use an existing virtual disk and point to the converted VMDK.
4. Boot the VM. The first XP boot will detect the new HAL; let XP re-detect Plug and Play devices and reboot twice.
5. Re-activate Windows by phone. The hardware fingerprint change is detected by the XP activation server (which Microsoft no longer operates), so you must call the activation IVR line and read the new installation ID.

Installing Siemens STEP 5 in the XP Guest

1. Mount the S5-DOS installation media as the virtual CD-ROM.
2. From an XP command prompt, navigate to D:\INSTALL (or your media drive letter) and run INSTALL.EXE. The installer is text-mode and runs entirely inside the 80x25 DOS window.
3. Accept the default installation directory C:\S5. Avoid paths with spaces; the S5W shell does not quote them and will fail on program launch.
4. When prompted for the COM port, select COM1 unless you are using a USB-to-serial adapter on COM2. STEP 5 maps the COM port to a fixed I/O address (3F8h for COM1, 2F8h for COM2); this address is set in the VMX:
   
   serial0.present = "TRUE"
serial0.yield = "TRUE"
serial0.fileName = "auto-detect"
5. Run S5W.EXE to verify the Windows shell launches. The 80x25 DOS sub-window inside S5W is normal; do not try to resize it.
6. Apply the STEP 5 V6.6 update by running SETUP.EXE from the update media. This step replaces the S5W shell with the modern Common Dialogs wrapper and is required for online connection to S5-155U CPUs.

DOS Window Behavior and Full-Screen Considerations

The S5W shell launches S5.EXE inside a Win32 console window. The console window inherits the 80x25 cell size from %SystemRoot%\System32\cmd.exe and cannot be resized live because S5.EXE queries the screen geometry once at start and re-queries the Win32 console only on window-creation events.

If a full-screen, borderless display is required:

• Set the XP console properties (right-click the title bar → Properties → Layout) to Width 80, Height 25, Window size: 80x25, and uncheck Let system position window.
• In the VMX, set svga.maxWidth = "1024" and svga.maxHeight = "768" so VMware always opens the guest display at a fixed resolution. The S5W shell will then fill the entire screen with its 80x25 character cells at 12x24 pixel font.
• If you need a true full-screen DOS environment (for example, to run S5-DOS standalone against a parallel port AS511), install FreeDOS 1.3 in a second VMware guest and skip Windows entirely. Configure the parallel port in the VMX:
  
  parallel0.present = "TRUE"
parallel0.fileName = "auto-detect"
parallel0.bidirectional = "TRUE"

Shared Folders and USB Passthrough

Two I/O paths matter for moving STEP 5 projects between the XP guest and a modern host: shared folders (for S5 program files) and USB passthrough (for the AS511 cable).

Shared Folders

1. With the VM powered off, open VM → Settings → Options → Shared Folders.
2. Click Add, browse to the host folder (for example D:\STEP5_PROJECTS), and enable Always Enabled and Map as a network drive in Windows guests.
3. Assign drive letter Z: to keep STEP 5 path statements short.
4. Inside XP, the shared folder appears as \\vmware-host\Shared Folders\STEP5_PROJECTS. The S5W project save dialog can browse this path directly.

USB Passthrough for the AS511 Cable

1. Plug the Siemens USB-to-serial adapter (6ES5 734-1BD20 or 6GK1 551-1AA00) into the host.
2. Open VM → Removable Devices → [adapter name] → Connect (Disconnect from Host).
3. XP detects the FTDI or Siemens-proprietary USB-serial chip and assigns a COM port (typically COM3 or COM4).
4. Inside STEP 5, set the online interface to that COM port. The handshake (DTR, RTS, DSR) follows the AS511 protocol; no extra driver is required inside XP beyond the one VMware Tools injects.

VMware Workstation 25H2 3D Acceleration Issue and Workaround

Starting with the Workstation 25H2 release (May 2025), VMware switched the default 3D graphics renderer from the legacy vmwgfx driver to the dx11 (DirectX 11) host backend. Windows XP, Windows Vista, and Windows 7 guests do not have a DirectX 11 user-mode driver, and the legacy vmwgfx path is no longer compiled into the 25H2 hypervisor build. The result is black or flickering screens, lost mouse capture, and a hang inside S5W.EXE when the shell tries to redraw the project tree.

Workarounds, in order of preference:

1. Downgrade the hypervisor. Workstation Pro 17.6.4 (build 24810009) is the last build with full XP guest support and the vmwgfx legacy renderer. The community-published VMware Workstation 17.6.4 Windows XP guest reference lists every required setting and is the recommended baseline for STEP 5 deployments.
2. Disable 3D acceleration per VM. Edit the VMX and set:
   
   mks.enable3d = "FALSE"
svga.enable3D = "FALSE"
   This forces the guest to use the XP GDI software renderer. STEP 5 does not require hardware 3D, so performance is unaffected.
3. Pin the XP VM to 16-color VGA. Inside the XP guest, set Display Properties → Settings → Color quality to Medium (16-bit) or Low (8-bit). The 32-bit color path is what triggers the 25H2 fallback to the DirectX 11 backend.
4. Run the VM in Fusion 13.5 on a macOS host. Fusion 13.5 still ships the vmwgfx driver and is unaffected by the Workstation 25H2 change.

Verification and Testing

Run the following checks in order. If any step fails, do not proceed to a live PLC connection.

1. XP boot integrity. The XP desktop must appear within 60 seconds. A hang on agp440.sys or vga.sys indicates a 3D acceleration conflict; reapply Workaround 2 above.
2. COM port enumeration. Open Device Manager → Ports (COM & LPT). The USB-serial adapter must appear as Silicon Labs CP210x (Siemens 6ES5 734-1BD20) or FTDI USB-SERIAL CH340 (clone cables) with a COM number between 1 and 9. STEP 5 only supports COM1 to COM4 in the legacy shell; remap in Advanced → COM Port Number if needed.
3. STEP 5 offline test. Launch S5W.EXE, create a new project, and save it to Z:\TEST.S5D. The save dialog must list the shared folder. If the save fails with "Path not found", the VMware shared folder service is not running; restart it with net start vmhgfs.
4. STEP 5 online test against a simulator. Use the AG 90/95/115U simulator or a known-good S5-95U on the bench. From S5W, choose PLC → Online → Test. The CPU must report RUN or STOP within 3 seconds. A timeout indicates a bad AS511 handshake; check the DTR/RTS jumpers on the cable.
5. Project round-trip. Open the project in the host editor (Siemens STEP 7 V5.7 with the S5 import converter, or a third-party S5D reader), confirm the symbol table matches, and re-save. The round trip proves the shared folder transport is intact.

Troubleshooting Matrix

Reference: Useful Configuration Snippets

The following VMX additions bundle all the Workstation 17.6.4 recommendations for an XP STEP 5 guest. Save them at the end of the .vmx file before first boot.