Opening SIMATIC S5 .S5 Files in STEP 5 V7.2: IBH Softec Format Conversion

Field guide for automation engineers who receive a Siemens SIMATIC S5 program file carrying a non-standard .S5 extension instead of the canonical .S5D. The typical symptom: a customer hands over DFBACHER.S5, STEP 5 V7.2 rejects the file on open, and the symbol/comment files appear to be missing. The cause is almost always that the file was written by a third-party tool (most commonly IBH Softec's S5 for Windows) rather than by STEP 5 itself. This article documents the format distinction, the ST.S5D token convention, three recovery procedures, and the symbol/comment loss caveat.

1. Overview: SIMATIC S5 File Format Landscape

The SIMATIC S5 family (S5-90U, S5-95U, S5-100U, S5-115U, S5-135U, S5-155U) stores each executable program element as a separate disk file with a strictly typed extension. The on-disk structure is the same on EPROM, on the programmer's hard drive, and on a PC/PG running STEP 5 — it is a flat list of files, not a project archive.

The collective ST.S5D file is unique: it is a packed container that holds every SB (sequence block) in the program. The other block types are stored one file per block. A SIMATIC S5 program on disk is therefore a directory of files matching the tokens above.

2. The .S5 vs .S5D File Extension Distinction

STEP 5 V7.2 hard-codes the .S5D extension for its program block files and .S5L for its source / listing files. When the customer supplied a file with extension .S5, the Open dialog filter in STEP 5 does not display it, and even if forced into the project directory, the file manager does not classify it.

There are three plausible origins for an .S5 file:

1. IBH Softec S5 for Windows: the file was created and saved by the third-party IDE. S5 for Windows uses its own internal project representation and may export to .S5, .S5D, or its native .S5P project file format depending on user choice.
2. Hand-rename by a third party: someone re-saved the file from another development tool and stripped the token portion (e.g. renamed PB7.S5D to PB7.S5).
3. Documentation fragment: the file is not a program block at all but an extract, dump, or print job that was mislabeled by the originator.

To determine which case applies, inspect the file size, the file header, and the directory it arrived in. A valid S5 program block is normally between 32 and 16 384 bytes and starts with a 5-byte header (block number, block type, library flag, and a checksum byte). A file under 32 bytes or a file with no readable header is almost certainly not a valid block.

3. Why .S5 Files Exist: IBH Softec S5 for Windows

IBH Softec GmbH (Germany) developed S5 for Windows as an alternative IDE for the S5 line. It runs on standard Windows PCs without the proprietary PG hardware and uses an MPI / serial adapter to communicate with the PLC. The S5 for Windows environment stores the program in its own project file (.S5P) and uses auxiliary files with extensions including .S5, .S5L, and .S5D.

The relevant consequence: an S5 for Windows project can export individual blocks, and the export uses extensions that do not always match the STEP 5 token convention. A file with extension .S5 produced by S5 for Windows is, internally, a valid S5 program block — but the surrounding metadata and the choice of extension make it unrecognizable to STEP 5's file manager.

IBH Softec documented the project and block file format on its support pages. The key point for the field engineer: opening a third-party S5 for Windows project file in STEP 5 is not supported by Siemens or by IBH Softec. The two IDEs use different file filters and different block header conventions (S5 for Windows stores additional comment and symbol metadata in a sidecar file).

4. STEP 5 V7.2 Capabilities and Limitations

STEP 5 V7.2 is the last released version of the original STEP 5 programming package, distributed for Windows 95/98/ME/NT/2000/XP. It supports the full S5 CPU range from S5-90U to S5-155U, includes the S5-DOS toolkit, and provides the AG (Automation Gerät = PLC) online functions for upload/download via the COM port or an MPI adapter.

The single most important row in the table is the last one. The SIMATIC S5 PLC stores only the compiled program and configuration data. Symbol names, symbolic I/O addresses, and program comments are not downloaded to the PLC — they are kept in the PC's project directory only. If the customer did not supply the symbol and comment files alongside the .S5 file, the symbols and comments are gone forever and must be re-entered manually.

5. The ST.S5D Naming Token Convention

STEP 5 identifies a program block file by parsing the filename as TTn.S5D, where TT is the two-letter token and n is the block number. The ST token is special: it is the collective file for sequence blocks (SB). The file is named exactly ST.S5D with no number — every SB block in the program is packed into that single file.

Anything else — including a file named DFBACHER.S5 or PB7.S5 — is rejected at the file-association layer before the contents are even read. This is why the first recovery procedure (Section 6) starts with a rename.

6. Procedure A: Rename the File to Use the Token

This is the fastest and most common recovery path. It works when the file is a valid program block but lost its token and/or its D during a copy/rename by the originator.

6.1 Prerequisites

• STEP 5 V7.2 installed and licensed.
• A copy of the suspect file in a working directory.
• A hex viewer (e.g. the DOS DEBUG utility or a freeware hex editor) to confirm the block type.

6.2 Step-by-Step

1. Inspect the header. Open the file in a hex editor. Look at byte offset 0x02 — this is the block type code (0x00=OB, 0x01=PB, 0x02=FB, 0x03=DB, 0x04=SB, 0x05=FX, 0x06=DX). Also look at offsets 0x00–0x01: they encode the block number as a 16-bit little-endian integer.
2. Identify the correct token and number. For example, if byte 2 is 0x01 and bytes 0–1 are 07 00, the file is PB7.
3. Rename the file. From a Windows command prompt, run:

   ren DFBACHER.S5 PB7.S5D

   If the file is an SB collective (byte 2 = 0x04 with no number), rename to:

   ren DFBACHER.S5 ST.S5D

4. Move the file into the STEP 5 project directory. STEP 5 expects all blocks of one program in the same directory; the file manager reads the directory listing and matches tokens on demand.
5. Open the project in STEP 5. Use File > Open Project and select the renamed file. STEP 5 will add it to the program overview.
6. Verify the block. Right-click the block in the program overview and select Block Properties. The block number, type, length, and checksum should match the expected values. If the checksum is wrong, the file was corrupted in transit.

6.3 Verification

• The block opens in the STEP 5 editor and the LAD/FBD/ST source displays without errors.
• The cross-reference list (Edit > Cross-Reference) shows the block in its expected callsites.
• The block checksums (header byte 4) match the value STEP 5 recomputes on open. A mismatch means the file is corrupted or not a real S5 block.

7. Procedure B: Upload the Program from the S5 PLC

This is the only procedure that recovers both program and configuration when the source file is unusable. It also gives you a definitive answer to the question "is the file a valid S5 block?".

7.1 Prerequisites

• STEP 5 V7.2 with online functions (the standard install includes the AG-Online package).
• Physical connection to the S5 PLC. Two options:
  • Serial: PC <--RS-232--> AG via the Siemens AG-S5 cable (TTY/20 mA current loop or RS-232-C, depending on PLC side). The standard setting is 9600 baud, no parity, 8 data bits, 1 stop bit. Some CPUs support 19 200 baud.
  • MPI: PC <--USB--> MPI/DP <--MPI--> S5 using a PC-Adapter (USB to MPI/DP) at 187.5 kbit/s.
• The PLC must be in STOP or RUN with password disabled (or password known). Some S5 CPUs require a password for upload; the customer must provide it.

7.2 Step-by-Step

1. Set up the connection. In STEP 5, choose File > Online > Set Connection. Select AG-Online and the appropriate interface (COM1/COM2 for serial, or the MPI adapter for MPI).
2. Establish the link. Choose File > Online > Connect. STEP 5 will report the PLC type (e.g. AG 115U / CPU 944) and the operating state. If the connect fails, verify the cable pinout, baud rate, and PLC mode selector.
3. Read the program. Choose File > Online > Read PLC to PG. STEP 5 will pull every block (OB, PB, FB, DB, SB, FX, DX) plus the system data and store them in the current project directory with the correct *.S5D filenames.
4. Verify the upload. Compare the block count with the customer's documentation. Open each FB and confirm the STL source is intact.

7.3 Verification

• The block list in STEP 5 matches the documentation.
• Reading back (Write PG to PLC) and comparing with the source produces no diffs.
• The PLC enters RUN with the new program and the controlled process behaves identically to the previous state.

8. Procedure C: Acquire IBH Softec S5 for Windows

When the file is known to come from S5 for Windows and renaming does not work, the only path to recover the file with its native symbols and comments is to use the same IDE that wrote it.

8.1 Prerequisites

• License for IBH Softec S5 for Windows. The vendor offers a commercial license and a demo version. The demo version can read project files and view blocks but cannot save or write to the PLC.
• Access to the original project files, including the .S5P master and any symbol/comment sidecars.

8.2 Step-by-Step

1. Install S5 for Windows on a Windows PC (XP / 7 / 10 / 11 in compatibility mode is reported to work for current versions).
2. Open the original .S5P project. The IDE will list every block with its name and comment intact.
3. Export each block to .S5D format (the IDE's Export function). Place the exported files into a STEP 5 project directory.
4. Open the STEP 5 project. The blocks will be readable; the symbols and comments are recovered from the S5 for Windows sidecar during export, where supported by the export options.

9. Symbol and Comment File Recovery Caveats

The S5 family stores symbols in one of two ways:

• STEP 5: in a separate symbol file with extension .Z0 (or sometimes .S5L for listings). Symbol files live in the PG project directory, not on the PLC.
• S5 for Windows: in a sidecar binary file associated with the project. The S5 for Windows project .S5P contains a compressed symbol table.

If the customer only sent the .S5 file and no symbol file, the symbols and comments are unrecoverable. They must be re-entered either in STEP 5 (Editor > Symbols) or in a new S5 for Windows project.

10. Verification and File Integrity Checks

After any recovery procedure, run these checks before trusting the result:

1. Header checksum. Reopen the block in STEP 5 and confirm the checksum shown in Block Properties matches the byte at offset 4 in the file. A mismatch indicates corruption.
2. Block length sanity. Compare the block length reported by STEP 5 with the file size. Length discrepancy > 16 bytes usually means trailing garbage was appended during a copy operation.
3. Cross-reference list. Generate the cross-reference list (Edit > Cross-Reference). Every CALL/JU/JC reference should resolve to an existing block. Unresolved references indicate missing blocks in the recovery set.
4. Compile / re-save. Use File > Save Project to force STEP 5 to recompile and rewrite every block. Any block that fails to re-save is corrupted.
5. PG-to-PLC round-trip. Connect to a test PLC or a standby CPU, write the project, then read it back and compare. Any diff is a recovery error.

11. Troubleshooting Matrix

12. Quick Reference: Decision Flow

Use this flow to pick the right procedure for any incoming S5 file:

Field Notes

• Always keep an unmodified backup of the customer-supplied .S5 file before any rename or hex edit. The header is the only source of truth for the block type and number.
• STEP 5 V7.2 runs fine in a Windows XP virtual machine on a modern PC; the original installer is 16-bit but works under XP mode. Hardware-key (dongle) licenses may not survive a VM.
• For S5-115U and S5-135U/155U CPUs, the FX and DX blocks are enabled by a setting in the system data; if STEP 5 reports them as "unknown block type", the CPU does not support them.
• When the customer has both an S5 for Windows project and a STEP 5 project, prefer the STEP 5 project for maintenance: the symbol/comment files use the canonical format and round-trip cleanly through the PG.

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