S7-300 to S7-1500 Migration: When Testing Windows Are Weeks Apart

How do you migrate a PLC system when you can only test during planned shutdowns? 

One manufacturing customer reached out in June 2025 with a large S7-300 PLC project that needed to migrate to S7-1500. Their biggest constraint: they can only test during planned maintenance shutdowns—sometimes weeks or months between opportunities. Downtime isn't an option.

Their engineer is extremely proficient in Siemens PLCs and used the S7-300 to S7-1500 migration guide from Siemens' SiePortal. The basic migration went smoothly: checked block consistency, fixed program errors, used the Migration Tool to generate the intermediate file from TIA V19 to V20, and successfully compiled.

Then real-world testing started.

RFID Communication Blocks

The first issue: communication blocks used for reading RFID tags didn't migrate correctly. They found a Siemens document on migrating MOBY function blocks to S7-1500, but it was outdated and didn't work with newer TIA Portal versions.

Rather than troubleshooting the migrated block, we detailed steps to recreate the functionality using an RFID technology object. That worked.

Proprietary SCADA System

Next: communication between the S7-1500 and their proprietary EMES SCADA system. Built by a third party with no source code access, they needed to ensure communications would work exactly like they did with the S7-300.

We kept all data blocks non-optimized and enabled GET-PUT communications in the S7-1500 to match the old configuration. After testing, communications worked correctly.

We also provided guidance on getting VFD parameters from their existing G120 drives into TIA Portal—a straightforward process with Startdrive installed.

ProfiSafe Communications

During testing, ProfiSafe communications with other S7-300 PLCs using Siemens PN/PN couplers weren't working. Safety interlock signals that pass to multiple PLCs failed in the migrated S7-1500.

After digging through manuals, we found capability restrictions with communication blocks in their S7-1500 safety program and with the S7-300s they were communicating with. The SENDDP and RCVDP blocks were configured using the latest version. The solution: roll back to a previous version of the communication blocks to ensure compatibility. That worked.

Safety Logic Optimization

At a recent in-person meeting, we saw the migrated code running live. They're very happy with how it's working so far.

While examining the PLC code, we found portions of the safety logic that needed optimization for the S7-1500 architecture. This was a quick fix: rebuilding the F-runtime blocks, putting the safety logic back in, and properly configuring the F-runtime group properties.

Why This Worked

They're still testing and qualifying the migrated code, but so far everything is working as expected.

This migration worked because the customer, Siemens, and EandM worked as a team to resolve each issue thoroughly. When your testing windows are weeks or months apart, you can't afford to spend that time troubleshooting alone. Having a partner who's seen these issues before—RFID blocks that won't migrate, proprietary SCADA configurations, ProfiSafe compatibility problems—means you resolve problems faster.

The standard migration guide gets you most of the way there. The real-world issues that show up during testing? That's where experience matters.

Planning an S7-300 to S7-1500 migration? Schedule some time with one of our product specialists today.