Control System Retrofit: Migrating S5 and S7-300/400 to TIA Portal

We cover both starting points: S5 as well as S7-300/400 with STEP 7 V5.x and WinCC flexible, targeting an S7-1500 or S7-1200 with WinCC Unified. The scope covers site survey, re-documentation of undocumented legacy programs, program and HMI in TIA Portal, testing on target hardware, commissioning and handover. Based in Luxembourg; core area Saar-Lor-Lux and Switzerland, projects across the DACH region, commissioning worldwide.

Not in a single step. The route goes via STEP 7 V5.x: the S5/S7 converter turns the STEP 5 program into a STEP 7 project, and instructions it cannot convert are reworked by hand. Only then can the project be migrated to TIA Portal and switched to an S7-1500 — for heavily grown programs, a structured rebuild often makes more sense.

The plant keeps running, but spare parts are getting scarcer. Since 1 October 2025, Siemens has supplied S7-300 and ET 200M modules only as spare parts or through repair, with availability stated until 2033. No need to rebuild immediately — but time to plan the migration rather than rush it after a failure.

Essentially yes — the S7-1500 supports STL. A few constructs no longer exist there, such as the master control relay or the ENT and LEAVE instructions; the migration log lists them, and they are adapted by hand. The S7-1200 has no STL, so the blocks are rewritten in LAD, FBD or SCL.

A component retrofit usually costs considerably less than building a complete new control cabinet, because the cabinet and wiring stay in place. The site survey sets the specific frame: after it, we quote the engineering at a fixed price, while commissioning is usually billed on a time basis, because it depends on the mechanical and electrical work being ready. Only the automation level is replaced; how large the scope turns out depends on the existing installation. That is why every project starts with the site survey, before any estimate.

Programming and the complete system test run beforehand in the test setup — at the plant it is only a matter of rebuilding, testing and starting up. The downtime window is therefore typically an extended weekend to a few days, and it is known before the rebuild.

Yes — this case is more common than you might think. The online program is uploaded from the CPU; it provides the plant logic even though symbols, comments and SCL sources are missing. The symbol table is reconstructed from the circuit diagrams, and the program is then rebuilt in readable FBD instead of being carried over unreadable. Strictly speaking this is no longer a migration but a re-engineering — with the advantage that your plant ends up with a documented, maintainable software base again.

In most cases, no: the automation level is replaced, the cabinet and its wiring stay in place. If the cabinet really is at the end of its life, a control-cabinet-building partner company handles the new build — software, visualization and commissioning remain from a single source.

Revised circuit diagrams showing the plant's real final state, complete symbol tables and block documentation, HMI operating documentation and training for operators and maintenance. For failsafe programs, the safety records from the software side are added: documented safety functions, achieved performance level, F-parameters and test records. What we don't take on is the CE assessment itself — we provide software and engineering services and don't place machinery on the market. Conformity assessment and declaration remain with the operator or the machine manufacturer; our documents feed in there as evidence. All details on the process are in the retrofit guide on the blog.