Converting STEP 7 Lite .k7p Backup to STEP 7 Professional V5.5

Overview

STEP 7 Lite was a free Siemens engineering tool used to program SIMATIC S7-300, S7-400, ET 200S, ET 200M, and M7-300/400 controllers. It stored complete projects in a single compressed archive with the extension .k7p (Komprimiertes 7-Projekt) and a single project database with the extension .s7l. STEP 7 Professional V5.5, the full commercial version, uses a multi-file project with the extension .s7p (Step 7 Project) and a different underlying database format (Global, hOmSave7, S7WkPna subfolders). The two tool chains cannot exchange projects directly through the SIMATIC Manager GUI, but three field-proven recovery paths exist.

This article documents the procedure for converting an .k7p backup into a STEP 7 Professional V5.5 project so the PLC program can be edited, recompiled, downloaded, and verified against a SIMATIC S7-300 CPU, including the S7-300 variants deployed inside SINUMERIK CNC milling systems where the PLC is integrated with the NCK and HMI.

Problem: .k7p Cannot Be Opened in STEP 7 Professional V5.5

A typical field scenario:

• Original commissioning was performed on a PC that had STEP 7 Lite V3.0 installed.
• The complete project was archived to a single .k7p file using File → Archive in SIMATIC Manager Lite.
• The maintenance PC available today has only STEP 7 Professional V5.5 (with or without a service pack).
• Double-clicking the .k7p file in Windows Explorer opens the archive in a viewer, but the Retrieve dialog in STEP 7 V5.5 rejects the file with a message such as "The selected file is not a STEP 7 archive" or simply does not list the file extension in the Files of type dropdown.

Root Cause Analysis

The .k7p format is a ZIP-compatible archive that wraps a single-file STEP 7 Lite database (.s7l), which in turn holds the program blocks (OB, FB, FC, DB, SFB, SFC, UDT), symbol table, hardware configuration (in *.s7hcfg form), source files, and the cross-reference data. STEP 7 Professional V5.5 uses a directory-based project layout (one folder per S7 program, plus a Global folder for language files, hOmSave7 for offline hardware, and S7WkPna for connection data). The schemas are different enough that a simple file-level conversion is not feasible, and Siemens did not provide a direct Open path between the two tools.

Solution Path 1: Integrated "Convert STEP 7 Lite" Tool (STEP 7 V5.5 SP4 or Later)

Starting with STEP 7 V5.5 SP4 (released as Entry ID 21927787 on the Siemens Industry Online Support), Siemens integrated a dedicated converter in the SIMATIC Manager installation. The tool reads a STEP 7 Lite project (.s7l) or archive (.k7p) and produces a standard STEP 7 Professional V5.5 project tree.

Prerequisites

• STEP 7 Professional V5.5 with at least Service Pack 4 installed. Verify via Start → SIMATIC → STEP 7 → Information or right-click on the S7BIN directory and check the version of SIMATIC_MGR.exe (file version 5.5.4.x or higher).
• Local administrator rights on the engineering PC.
• At least 500 MB free disk space for the converted project plus working buffer.
• The original .k7p file or an already-retrieved .s7l file.

Step-by-Step Procedure

1. Install or upgrade to STEP 7 V5.5 SP4 or later. The package is delivered as S7V55SP4.exe (or higher) and is patched on top of the existing V5.5 base installation.
2. Confirm the converter entry exists. After installation, navigate to Start → SIMATIC → STEP 7 → Convert STEP 7 Lite. If the entry is missing, run SETUP.EXE from the SP4 media and select Modify installation → Convert STEP 7 Lite.
3. Launch the converter. A wizard opens with two pages: Source and Target.
4. On the Source page, click Browse and select the .k7p file. The tool extracts the embedded .s7l into a temporary directory under %TEMP%\STEP7_Convert\<random>.
5. On the Target page, specify an empty target directory. The converter creates a fully populated STEP 7 V5.5 project structure at this location.
6. Click Convert. The wizard displays a progress bar and a log of migrated objects (S7 program, blocks, symbol table, sources, system data, HW Config, connections). The typical conversion for a 2 MB .k7p containing 350 blocks takes 20-60 s on a current Windows 10/11 workstation.
7. When the conversion finishes, click Finish and start the SIMATIC Manager.
8. In the SIMATIC Manager, choose File → Open → User Project and navigate to the target directory. Select the generated .s7p file.
9. The project opens with one S7 program, one CPU (S7-300 family), and the full block container. Run PLC → Compile and Download Objects only after verifying the hardware (see Verification below).

Solution Path 2: Reinstall STEP 7 Lite V3.0

If the engineering PC runs STEP 7 V5.5 SP1-SP3 (or an older V5.4), the integrated converter is not present. The supported alternative is to install STEP 7 Lite V3.0 alongside STEP 7 Professional.

Prerequisites

• STEP 7 Lite V3.0 installation media. Siemens has re-published the package as a free download specifically for migration scenarios. Search the Siemens Industry Online Support for Entry ID 21462916 ("STEP 7 Lite Available for Free Downloading").
• The PC must satisfy the original STEP 7 Lite requirements: Windows XP SP2 / Windows 7 (32-bit), at least 512 MB RAM, 1.5 GB disk space.
• STEP 7 Professional and STEP 7 Lite can coexist because Lite uses a separate registry hive and its own SIEMENS\STEP7_Lite program directory; there is no DLL conflict.

Step-by-Step Procedure

1. Disable UAC (User Account Control) and any real-time virus scanner that interferes with SIEMENS\STEP7\S7BIN\S7CNVEX.EXE registration.
2. Run setup.exe from the STEP 7 Lite V3.0 distribution. Choose Install and accept the default path C:\Program Files\Siemens\Step7Lite.
3. Reboot when prompted. The SIMATIC Manager (Lite) icon appears on the desktop.
4. Start the SIMATIC Manager (Lite).
5. Choose File → Retrieve, set the file type to STEP 7 Lite archives (*.k7p), and select the .k7p file. The tool extracts the embedded .s7l to disk.
6. Open the retrieved .s7l project and verify the block container and symbol table are present.
7. Now use STEP Lite to Re-archive the project as a standard STEP 7 V5.x .zip: File → Archive, select a target .zip file, choose With reorganization to defragment the Lite database, and confirm.
8. Start the regular SIMATIC Manager (Professional) and choose File → Retrieve on the generated .zip archive. STEP 7 V5.5 will produce a standard .s7p project in the chosen directory.
9. Open the project, run PLC → Compile on every block, and then proceed to the verification steps.

Solution Path 3: Manual Block-by-Block Recovery

If neither the converter nor STEP 7 Lite is available, the .k7p archive can be opened with any ZIP utility (7-Zip, WinRAR) and the blocks extracted in STL / SCL source form. This is the last-resort path because the hardware configuration, symbol table, and connection data cannot be recovered automatically.

1. Rename the file from project.k7p to project.zip and open it with 7-Zip.
2. Navigate to the OmContainer subfolder; blocks are stored as *.bin with the block number encoded in the filename (e.g. OB1_FC10_001.bin). Export the entire folder.
3. Build a new STEP 7 V5.5 project skeleton manually: File → New Project, name it, insert an S7-300 station, configure the rack in HW Config with the correct order card, IM, and signal modules (refer to the wiring diagram of the CNC).
4. Re-create the symbol table by transcribing it from a printout, or use the OmContainer\Symbols\*.s7s export from the .k7p.
5. Import the block sources via Options → Manage System Data Sources or by retyping. For each .bin, open it in STEP 7 V5.5 with File → Open and set the file filter to All files (*.*); STEP 7 recognizes the block header and offers to insert it into the program.
6. Run PLC → Compile All, then re-attach the system data (HW Config → Station → Save and Compile).

Verification After Conversion

Always validate a converted .k7p project on a test bench before downloading it to a production CNC. The following matrix is the minimum verification scope.

Online Test Procedure

1. Connect the engineering PC to the S7-300 CPU via MPI/PROFIBUS or Ethernet (CP 343-1 Lean / CP 343-1).
2. Set the PG/PC interface to TCP/IP → Network card or PC Adapter (MPI) as appropriate.
3. Open the project, right-click the S7 program and select Download. Select Download to target system → All with Overwrite target system.
4. After the download, the CPU should restart in RUN; if it goes to STOP, read the diagnostic buffer (PLC → Diagnostic/Setting → Module Information → Diagnostic Buffer) and resolve any OB-not-loaded or interface-time-error entries.
5. Force I/O on a safe output (e.g. status indicator) to confirm the symbol-to-address mapping is intact.

S7-300 Specific Considerations for CNC Restoration

When the S7-300 lives inside a SINUMERIK 810D / 840D / 840D sl milling system, several additional constraints apply:

• The PLC program uses standard DB blocks that mirror the NCK interface (DB 10, DB 11, DB 20, DB 21–DB 30, DB 31–DB 38 for axis signals, DB 50 for HMI signals). These DBs must be regenerated by STEP 7 after conversion to match the active NCU software version; the .k7p may contain a snapshot from a different NCU version.
• The HMIsvr block folder (if present) holds SINUMERIK Operate integration blocks. They are not converted by the integrated tool and must be obtained from the matching SINUMERIK toolbox.
• If the original project contained a subnet configuration between the S7-300 CP and the NCU CP, the FDL / S7 connection data in S7WkPna must be re-validated; PROFIBUS addresses and timing may shift between NCU software versions.
• Backup before download: PLC → Upload Station to PG while the CNC is in a safe state (e.g. reset, no part program active) and archive the result separately.

Troubleshooting Matrix

Long-Term Recommendation: Migrate to TIA Portal

STEP 7 V5.5 and STEP 7 Lite are legacy tool chains. For new projects Siemens recommends TIA Portal (currently V18 / V19). Migration from a converted STEP 7 V5.5 project to TIA Portal is performed with the Migrate project function. TIA Portal provides native online backup, integrated safety, and a unified PLC / HMI / Drive environment that is mandatory for modern SINUMERIK ONE and SIMATIC S7-1500 systems. See the Backing up an online CPU documentation for the current recommended backup procedure on S7-1200 / S7-1500 controllers as a template for the migration target.