The End of an Era: Siemens Discontinues S7-300
The Siemens SIMATIC S7-300 has been the workhorse of German industry for decades. Robust, proven, widely deployed. But Siemens has announced the end-of-life for this platform: spare parts are becoming scarcer, official support is being phased out, and new projects are targeting SIMATIC S7-1500 with TIA Portal.
For operators of systems with S7-300 controllers, this raises an urgent question: When and how to migrate — and what can go wrong?
Why Migration Is Not a Simple One-to-One Swap
The biggest misconception about PLC migrations: the new controller is simply installed, the old program is transferred, and everything continues as before. In practice, this is rarely the case.
Differences in Programming Language and Structure
S7-300 programs are often written in STL (Statement List) or FBD (Function Block Diagram) — sometimes since the 1990s, by different programmers, without uniform documentation. TIA Portal favors different structures, and not every program logic can be transferred one-to-one.
Timing Differences
The S7-1500 is significantly faster than the S7-300. What sounds like an advantage can cause problems: programs built on specific cycle times can behave differently than expected. Response times for sensors and actuators must be re-evaluated.
Changed Hardware Interfaces
Signal modules, communication cards, and fieldbus connections differ between generations. A thorough inventory of existing hardware is mandatory before a single line of code is touched.
Outdated or Undocumented Programs
For systems that have been running for 20 years, documentation is often completely absent. The original programming team is no longer available. The program runs — but nobody knows exactly why anymore. In such cases, the logic must be reverse-documented before it can be migrated.
The Methodical Approach
Step 1: Inventory and Analysis
Before any decision, a complete inventory is essential: What hardware is installed? Which software version is running? Which interfaces exist? Is there documentation — and if so, how current is it?
The program is read out, backed up, and analyzed. Every block, every data structure, every communication connection is recorded.
Step 2: Create Migration Concept
Based on the analysis, a concept is developed: What can be directly transferred? What needs to be reprogrammed? Which hardware components will be replaced? And — crucially — how will the switchover be performed during operation or with minimal downtime?
Step 3: Parallel Operation and Simulation
Where possible, the new controller is set up in parallel with the old one and verified with a simulator or test setup. This way, errors are discovered in a safe environment — not on the running system.
Step 4: Commissioning and Testing
Commissioning is performed step by step, with close support. Every function is tested, every interface checked. Safety functions are verified with particular care.
Step 5: Documentation and Training
After successful migration, the entire system is documented: circuit diagrams, terminal diagrams, network diagrams, commented program code. Operating personnel are trained in using the new controller and the TIA Portal interface.
Typical Mistakes in PLC Migrations
- Time pressure as a driver: Migrations that are rushed only because the old controller has just failed frequently result in extended downtime.
- Lack of simulation: Anyone who does not sufficiently test the new program before deploying it to the system risks production outages.
- Underestimated documentation effort: Undocumented legacy programs require more analysis time than planned — this must be realistically budgeted.
- Neglected peripherals: The PLC is the brain, but the system has many organs. Sensors, actuators, variable frequency drives, and communication partners must all be compatible with the new controller.
When Is Migration Worthwhile?
A migration is almost always worthwhile when:
- Spare parts for the existing controller are no longer available,
- the system is strategically important and planned for further years of operation,
- cycle time optimization or system expansion is planned anyway,
- or when downtime caused by the old controller is already generating costs.
Ampere Partner performs PLC migrations from S7-300 to TIA Portal — nationwide, with a methodology that minimizes risks and keeps downtime as short as possible.