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Migrating Siemens S7-300 to S7-1500

Enhanced Control Solutions · · 9 min read

The S7-300 has run more UK production lines than almost any other controller, and Siemens is retiring it. Siemens’ own S7-300 page says the S7-300 and ET 200M system families “will be available until 2033”. Siemens said in 2023 that the phase-out would be announced that October, with new parts orderable for around two years and a spare-parts phase of about eight years after that. Distributors widely report the phase-out announcement (PM400) as 1 October 2023 and the move to spare-part supply only (PM410) as 1 October 2025. In other words, the S7-300 is now for keeping existing machines running, not for building new ones.

So nothing stops working, but every year the S7-300 stays in service, spares get scarcer and dearer and the engineers who know STEP 7 Classic get fewer. This guide covers the route Siemens recommends, what the software conversion actually does, and how to plan a cut-over that does not gamble the line.

Where to migrate to

Siemens maps the S7-300 CPU to the S7-1500, and S7-300 and ET 200M I/O to ET 200MP (S7-1500 I/O) or ET 200SP. For process plants, distributors also point to the S7-400 and ET 200SP HA.

Two hardware differences shape the design early:

  • No expansion racks. An S7-300 could have up to four racks of eight modules, linked by IM 360/361 or IM 365. The S7-1500 is central only, with up to 32 modules on its own rail. Where the old system used expansion racks, plan for more PROFINET distributed I/O.
  • System power. The S7-1500 uses its own system power supply (for example the PM 1507) linked to the modules by a U connector.

Keeping the field wiring

S7-300 and S7-1500 front connectors are different parts, so the old connector does not simply move across. Siemens’ Interface Module Adapter (IMA, the 6EZ2041 range) is the route for keeping field wiring: the adapter takes the existing wiring and is pre-wired to the new S7-1500 module. Siemens is clear that there are not adapters for every module combination, that voltages, potential groups and cooling need checking, that module parameters must be reconfigured, and that it recommends a field test before switching over generally. The adapter housing also needs cabinet space, so measure before you order.

ET 200M remote I/O can stay for now. Siemens lists ET 200M as supported under an S7-1500, either on PROFIBUS through a CPU with a DP interface or a CM/CP, or on PROFINET by changing the interface module. That is a useful way to stage the work: replace the CPU first, and the I/O later. But ET 200M is in the same phase-out as the S7-300, so keeping it defers the I/O problem rather than solving it. Siemens’ own recommendation is a full move to ET 200MP or ET 200SP on PROFINET.

Converting the program

The conversion runs in two steps.

1. Migrate the STEP 7 project into TIA Portal. Siemens requires the project to be at STEP 7 V5.4 SP5 or later first: open it, run a consistency check and compile it there. Multi-projects cannot be migrated as a whole, know-how-protected blocks must have their protection removed, and GSD files for third-party devices must be installed. The migration itself is either “Migrate project” inside TIA Portal (with STEP 7 V5.x on the same PC) or Siemens’ Migration Tool, which creates an intermediate file on the old PC. There are reports that recent TIA Portal versions (V20) no longer migrate STEP 7 V5.x projects, so confirm this for the version you plan to use; if necessary, migrate in an earlier version and upgrade the TIA project afterwards.

2. Change the device to S7-1500. Siemens is explicit that “the CPU is not automatically changed to the S7-1500 during the migration process”. You run “Migrate to S7-1500” on the CPU, and only the CPU is adjusted: every other central module has to be added again, with the original I/O addresses matched. Record every module and its addresses before you start.

What needs rework

Siemens’ own advice is “not to implement the S7-300/400 programs without any changes”. The usual work:

  • Block access stays “standard”. Migrated blocks keep standard access. Moving to optimised access improves performance, but optimised blocks do not support AT views, direct absolute access or pointer-based indirect addressing, so that code has to be rewritten using slices, arrays with an index or VARIANT.
  • STL behaves differently. On the S7-1500, accumulators and the status word are not passed between blocks, the DB register is reset after each fully qualified access, and the Master Control Relay is not available. Code that relied on these needs rewriting, often in SCL.
  • Temporary data changes. TEMP variables in optimised blocks start at defaults; code that relied on leftover values will behave differently.
  • Timers. S5 timers and counters still work as legacy instructions, but Siemens recommends IEC timers. IEC timers on the S7-1500 update when they are called or their outputs are read, which can catch out logic that reads the output several times in one scan.
  • System functions are renamed. For example BLKMOV becomes MOVE_BLK. Siemens publishes a comparison list.
  • Alarms. ALARM_S, ALARM_SQ and ALARM_SC are not supported; they become Program_Alarm.
  • Start-up and faults. The S7-1500 always warm-restarts and stops on far fewer faults than an S7-300. Programs that relied on a missing OB stopping the CPU need reviewing.
  • Communications. MPI is not supported. CP 340/341 serial links move to CM PtP modules. S7 communication (GET/PUT, BSEND/BRCV) still works between old and new CPUs, which helps during a staged cut-over.
  • Safety programs. Some F-instructions must be deleted and reinserted, and recompiling for the S7-1500 creates a new F-signature, so the safety acceptance has to be repeated.
  • HMIs. Panels from the 70, 170 and 270 series and the MP 177/277/377 are not supported in current WinCC (TIA Portal) and are replaced by Basic or Comfort Panels during migration. WinCC flexible projects need to be at 2008 SP2 or later. Check cut-outs and the change from 4:3 to widescreen.

Siemens also warns that migrated programs “may run slower” until they are adapted to the S7-1500, and recommends a full function test after migration.

Planning the cut-over

Siemens describes three approaches. Hot: old and new run side by side until the new system is proven; lowest risk, highest cost. Warm: the new system is installed alongside and signals are switched during a planned stop. Cold: the old system comes out and the new one goes in during a standstill; cheapest, but with the longest outage and the most risk.

Whichever you choose, the same steps make it predictable:

  1. Audit what is installed. CPUs, I/O, technology modules (counter, PID and positioning modules map to S7-1500 technology objects, while freely programmable modules such as the FM 352-5 need individual analysis), HMIs, comms and firmware.
  2. Take current backups and compare them online. Migrate the program that is running, not the one on a laptop.
  3. Migrate and read the log. Every warning is a decision.
  4. Test before site. Simulate against the machine’s functional description (PLCSIM Advanced is the usual tool), and agree what “proven” means before the stop.
  5. Keep a way back. Keep the S7-300 program and hardware available until the new system is signed off, and define the point of no return in advance.

Licences

STEP 7 Basic only covers the S7-1200, so it cannot be used. You need STEP 7 Professional (TIA Portal), plus a valid STEP 7 V5.x licence to open the source project; the Professional Combo licence covers both. HMI projects need WinCC (TIA Portal), and safety programs need STEP 7 Safety Advanced.

How ECS approaches it

The hard part of an S7-300 migration is rarely the conversion. It is knowing exactly what is installed, which program is really running, and which modules have no simple replacement. A Capture audit records every device, backs up every reachable program and flags what is in phase-out, so the plan starts from facts. The migrated projects, versions and cables are then held in Command Centre.

We carry out S7-300 migrations, panel modifications and commissioning in-house as part of our automation projects, usually staged so the line keeps running. If an S7-300 fails before the plan is ready, emergency support can help get it back.

Sources

Lifecycle dates for individual modules can differ. Check a specific order number with Siemens before buying or planning around it.

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