Siemens STEP 5 Software Versions, Compatibility, and S5-100U

Overview

Siemens STEP 5 is the legacy programming environment for the SIMATIC S5 family of programmable logic controllers, including the S5-100U, S5-115U, S5-130U, S5-135U, and S5-155U. The software originated in the 1980s as a DOS-based package and evolved through several releases ending with the final SIMATIC STEP 5 V7.2 in 2001. The original software is no longer distributed through standard Siemens sales channels, but it remains in active use on installed machines worldwide, particularly in industries where the S5-100U was deployed for small standalone applications. This reference documents the version history, hardware compatibility, TTY interface requirements, and current support paths including virtual machine deployment for modern operating systems.

STEP 5 Version History and Release Timeline

The following table summarizes the documented releases of STEP 5 programming software. The earliest on-line manual available through Siemens documentation channels corresponds to V6.0 (1996). The MLFB (Siemens order number) for the original V6.0 German manual is 6ES5 896-0SC11.

The STEP 5 /ST variants are the Windows 3.11/95/98 builds. The S5-DOS variants run in DOS or DOS-mode only. The V7.x packages added support for newer PG (programmer) hardware and improved cross-listing, but retained the same Statement List (ST), Ladder Diagram (LAD), and Control System Flowchart (CSF) editors that have been present since V3.0.

Hardware and Operating System Compatibility

STEP 5 was developed for an era of computing hardware that pre-dates modern Windows platforms. The compatibility matrix below reflects field-verified behavior, not theoretical capability:

Field experience indicates the DOS-based STEP 5 versions operate reliably on Pentium-class hardware at clock speeds of 200 MHz or less. Above 200 MHz, timing routines in the serial port drivers may fail to initialize correctly because the original code uses software delay loops calibrated for older CPUs. A VM with a virtualized slow serial port avoids this problem entirely.

S5-100U Specific Programming Considerations

The S5-100U is the smallest member of the SIMATIC S5 family, designed for compact standalone applications. Its CPU modules (CPU 100, CPU 102, CPU 103) have a non-expandable program memory ranging from 1 KB (CPU 100) to 20 KB (CPU 103). Programming concerns specific to the S5-100U include:

• Program organization blocks (OB): OB1 is the cyclic scan; OB21, OB22 are warm/cold restart handlers. The S5-100U has no support for OB31 to OB34 (time-of-day interrupts).
• Function blocks (FB) and Program blocks (PB): Limited set. PB 0 through PB 255 are addressable, but practical memory constrains active blocks.
• Data blocks (DB): DB 2 through DB 255 user-defined. DB 1 is reserved for system data.
• STEP 5 statement set: The S5-100U supports the basic operation set (A, AN, O, ON, S, R, =, JU, JC, etc.) but does not support the extended operations available in the S5-115U and above.
• No special function blocks (FB special): The S5-100U has no intelligent I/O modules; therefore, third-party tools marketed as "STEP 5 for Windows" that omit special FB handling are perfectly adequate.

For pure S5-100U work (upload, edit annotations, download), a streamlined tool such as the IBHsoftec S5 for Windows package is sufficient. For S5-115U/135U/155U systems with intelligent I/O, the full Siemens STEP 5 V7.2 with the special function block editor is required.

TTY Interface and Cable Requirements

All S5 PLCs communicate over a 20 mA current-loop (TTY) interface, not RS-232. To program an S5-100U from a modern PC, you need a TTY-to-RS-232 converter or a TTY-to-USB adapter. The Siemens PG 740 and PG 760 programming devices had a built-in TTY port and shipped with the full STEP 5 software pre-installed on internal hard drives. Restoring one of these PGs to working order is often the simplest path to legal STEP 5 access for sites that already own the hardware.

Pinout reference for TTY current loop

Third-Party STEP 5 Alternatives

Several third-party vendors have produced STEP 5 compatible programming tools that remain commercially available. These provide a legal alternative to hunting for legacy Siemens installation media.

• IBHsoftec S5 for Windows: Windows-native STEP 5 programming environment. Supports all S5 CPU families. Includes an S5-to-S7 source conversion utility that translates STL/FBD/CFC code to STEP 7 STL, though manual rework is typically required for function blocks using S5-specific operations.
• Deltalogic SoftPLC: Soft-PLC runtime that emulates S5-100U behavior on a PC, including simulated I/O. Useful for offline testing of recovered S5 programs without connecting to physical hardware.
• Mitsubishi GX Works / CoDeSys-based remap tools: For new installations, migration to a modern PLC family may be more cost-effective than continued S5 maintenance.

Migration to S7 / TIA Portal

For installations where the S5-100U is being upgraded to a S7-1200, S7-1500, or ET 200S CPU, the recommended migration path is:

1. Upload the S5 program using STEP 5 V6.6 or V7.2 and the original TTY interface. Save the program in S5-DOS format to disk.
2. Convert to S7 source using the IBHsoftec S5-to-S7 conversion utility, or manually re-enter the logic. The S5 operation set maps to S7 STL as follows: A -> A, AN -> AN, O -> O, S -> S, R -> R, JU -> JU, JC -> JC. Counter and timer operations (C, T) require conversion to S7 function blocks because the S5 word-oriented counter model differs from the S7 IEC 61131-3 counter model.
3. Rewire the I/O from the S5-100U front connector to the S7 terminal block. Note that the S5-100U uses blade-type connectors; S7-1200 uses push-in or screw terminals.
4. Validate I/O addresses. The S5-100U defaults to I0.0-Q0.7 (byte 0). S7-1200 defaults to I0.0-Q0.7 with byte-aligned addressing that maps directly.
5. Commission in dry-run mode before cutting over the field wiring.

Windows 10 / Modern OS Support via Virtual Machine

Siemens support has confirmed that there is no native Windows 10 build of STEP 5. The official support path is to deploy STEP 5 inside a virtual machine. The recommended configuration, per Siemens industrial support:

1. Install a hypervisor such as VMware Workstation, VMware Fusion (macOS), Oracle VirtualBox, or Hyper-V on the Windows 10/11 host.
2. Create a VM with Windows XP SP3 or Windows 7 SP1 as the guest OS. Windows 98 SE can also be used but has limited USB passthrough support.
3. Install the Siemens STEP 5 USB-Serial driver inside the VM, and map the host USB port to the guest.
4. Install STEP 5 V7.2 in the guest OS. The installer runs cleanly on Windows XP SP3.
5. Connect to the S5 PLC through the USB-to-TTY adapter from within the VM.

Siemens also provides a pre-configured VM image containing STEP 5 and a tested USB-Serial solution. This image is not downloadable from the public Siemens support portal; it must be requested through the Siemens industrial hotline. For North America, the hotline number is 1-800-333-7421. Request the "STEP 5 VM with USB-Serial" package. Additional information is available in the Siemens SiePortal thread on STEP 5 for Windows 10.

Program Upload Procedure (S5-100U, Reference Workflow)

To upload an existing program from a S5-100U using a modern PC and USB-to-TTY adapter, follow the procedure below. This workflow assumes STEP 5 V7.2 is installed in a Windows XP VM with a USB-to-TTY adapter mapped to a virtual COM port (typically COM1 inside the guest).

1. Power the S5-100U. Verify the CPU "RUN" LED is on steady or flashing (STOP is acceptable for upload).
2. Connect the TTY cable from the CPU's 20 mA port to the USB-to-TTY adapter. Plug the adapter into the host PC.
3. Confirm the COM port inside the VM. Use Device Manager -> Ports (COM & LPT) to verify the port number.
4. Set the COM port parameters: 9600 baud, 8 data bits, even parity, 1 stop bit, software (XON/XOFF) flow control. Do not use hardware handshaking.
5. Launch STEP 5 V7.2. From the File menu, select PLC -> Upload to PG (or AG -> Datei in PG laden in the German UI).
6. Select the target blocks to upload: OB1, all PB, all FB, all DB.
7. Save the uploaded program to disk in S5-DOS format (*.S5D).
8. Generate a cross-reference (Editor -> Cross-Reference) and a documentation printout (File -> Print) as a backup reference before any modifications.

Troubleshooting Matrix

Specifications and File Format Reference

Notes on Documentation Access

The Siemens support site maintains an archive of STEP 5 manuals under the legacy product documentation section. The earliest English-language manual available online corresponds to V6.0 (1996). Earlier versions (V3.0 in particular) exist primarily as German-only paper manuals, although a German/English bilingual PDF of V3.0 has been distributed informally. Manuals for V6.6 and later are available in English from the Siemens legacy documentation portal. The copyright notice on the current Siemens STEP 5 manual index page ("© Siemens AG, 1998, 2004") indicates that older paper manuals are unlikely to be re-scanned and published.