Migrating SIMATIC S5 to S7: Conversion Steps & FB Compatibility

Overview of SIMATIC S5 to S7 Migration

Thousands of SIMATIC S5 programmable logic controllers remain in service across process and manufacturing plants worldwide. End-of-life announcements from Siemens, combined with shrinking spare-part availability for legacy CPUs (S5-90U, S5-95U, S5-100U, S5-115U, S5-135U, S5-155U), make migration to the S7 family a recurring engineering task. Field experience shows that the migration is rarely a single-step operation, and the path chosen has long-term consequences for spare-part strategy, support contracts, and engineering tooling.

Siemens provides a formal Migration Guide: SIMATIC S5 to SIMATIC S7-1500 on the Siemens Industry Online Support portal. This guide is the canonical reference, but it covers only the S7-1500 target. No equivalent guide or automatic tool exists for the S7-1200, which means engineers must follow different procedures depending on which S7 platform the customer has standardized on.

Prerequisites and Target Platform Selection

Before launching the migration toolchain, decide which S7 platform will replace the S5. The decision drives the entire toolchain, the available migration tools, and the long-term support profile.

Many field engineers still prefer S7-300 / S7-400 on STEP 7 V5.5 / V5.6 for migration projects because of the maturity of the converter, the absence of TIA Portal instabilities on a production line, and the simpler spare-part model. This preference is explicit: the S7-300 / S7-400 with STEP 7 V5.x combination is regarded as the most predictable target until TIA Portal V14 (and successor) firmware problems on the S7-1500 are fully resolved.

Prerequisites Checklist

• STEP 5 source project (S5-DOS, S5 file container) — backup verified
• STEP 7 V5.5 SP2 or later installed (required for the S5 converter)
• TIA Portal V14 or V14 SP1 minimum, V15+ strongly recommended for new S7-1500 work
• License dongle for the converter option in STEP 7 V5.5
• Current S5 program listing and cross-reference
• Hardware list of all S5 modules, CPs, and I/O
• Communication topology map (Sinec L1 / L2 / H1 nodes)

Two-Step Migration Architecture

Direct migration from STEP 5 to TIA Portal is not supported. The official path requires an intermediate STEP 7 V5.5 project, and is documented in the Siemens migration guide and confirmed by field experience.

Figure 1 — Three migration paths: two-step to S7-1500, single-step to S7-300/400, and manual rewrite for S7-1200.

1. Step 1: Convert STEP 5 source to a STEP 7 V5.5 project using the bundled S5 converter. Output is a STEP 7 V5.5 .s7p archive.
2. Step 2: Migrate the STEP 7 V5.5 project to TIA Portal using the TIA migration tool. The target CPU is then an S7-1500 with a defined firmware version.

FB Conversion Compatibility Reference

The S5 converter in STEP 7 V5.5 handles a defined set of S5 standard function blocks (FBs) automatically. Field engineers maintain a published distinction between "convertible" FBs and "non-convertible" FBs because it drives the engineering hours for the conversion phase.

Non-Convertible S5 Standard FB Categories

The S5 program model relied on several layers of standard FBs that Siemens shipped with the programming package. Three categories of those FBs do not survive the migration to S7 in their original form, and attempting to convert them produces either a compile error or a silently non-functional block.

1. Display and Operator Panel Drivers

The S5 OP and COROS operator panels were driven by Siemens-supplied FBs such as FB51 and its siblings. These FBs read panel key states, wrote to display buffers, and managed the OP-protocol handshake. In S7, those functions are replaced by:

• ProTool / WinCC Flexible for S7-300/400 migrations
• TIA Portal WinCC for S7-1500 migrations
• Tag-based communication, with the panel protocol handled by the HMI runtime, not the CPU program

The CPU program must be scrubbed of all display-driver FBs before conversion. Field engineers report this scrub takes a non-trivial amount of time on large S5 programs because the FBs are often called from many OB1 segments.

2. Sinec L1 / L2 / H1 Communication FBs

Sinec was the Siemens proprietary network family for S5:

• Sinec L1 — low-speed, master/slave, used on AS-Interface-like segments
• Sinec L2 — PROFIBUS predecessor (corresponds to PROFIBUS DP / FMS)
• Sinec H1 — Industrial Ethernet predecessor (10 Mbps, CSMA/CD)

The S5 communication FBs (send/receive, fetch/write, BSEND/BRCV) that drove the CP 530, CP 1430, CP 1431 and the L1 master/slave FBs are not converted. The communication is re-implemented on the S7 side using:

• PROFIBUS DP via CP 342-5 / CP 443-5 (S7-300/400) or CM 1542-5 (S7-1500)
• PROFINET / Industrial Ethernet via CP 343-1 / CP 443-1 or the S7-1500 onboard PROFINET interface
• Open IE communication: TSEND, TRCV, TCON, TDISCON for ISO-on-TCP / TCP / UDP

3. COM-Package FBs (Closed-Loop Control and Special Libraries)

The "COM package" (Kommunikations- und Organisations-Pakete) bundled FB ranges for closed-loop control, positioning, and special communication. These FBs were typically called within the FB120-FB255 range in many S5 programs. In S7, their functionality is delivered by:

• Standard library blocks in STEP 7 V5.5: PID_CP, PID_FM, CONT_C, CONT_S
• TIA Portal technology objects: PID_Compact, PIDT1 in S7-1500, or external FM 355 / FM 455 modules in S7-300
• Motion control technology objects in S7-1500: TO_PositioningAxis, TO_SynchronousAxis

Communication Migration: Sinec to Modern Networks

One of the largest engineering tasks in a Sinec-bearing S5 program is the re-mapping of the communication layer. The table below summarizes the canonical mapping used in brownfield migrations.

For S7-1500 projects, consult the Siemens Industry Online Support knowledge base to retrieve the current CP compatibility matrix. The CP type and firmware version must be matched against the S7-1500 firmware version (V1.x through V3.x) to avoid communication faults at commissioning.

Step 1: STEP 5 to STEP 7 V5.5 Procedure

The STEP 5 to STEP 7 V5.5 conversion is the most mature of the migration steps. It is the same path used since STEP 7 V3.x and is documented in the STEP 7 V5.5 online help and the conversion tool's own user manual.

1.1 Prepare the STEP 5 Source

• Open the S5 program in STEP 5 V7.x (or STEP 5 for Windows). Verify the project compiles without errors.
• Print or export the cross-reference list. The S7 cross-reference format differs and the printout is the fallback when symbol conversion loses information.
• Identify and document all FBs that fall in the non-convertible categories (display drivers, Sinec, COM package).

1.2 Run the S5 Converter

1. In STEP 7 V5.5, choose File → S5 File → Open and select the S5 file container.
2. The converter analyzes OB, FB, PB, SB, DB, FX, FY, and the symbol table.
3. Mapping rules: S5 PB (program block) → S7 FC (function); S5 FB → S7 FB with instance DB; S5 DB → S7 DB with adjusted syntax; S5 OB → S7 OB family (OB1, OB100, OB101, OB102).
4. The conversion log is written to a .log file. Read it line-by-line; every warning must be triaged before the next step.

1.3 Review the Converted Project

• Open each converted block in the STEP 7 V5.5 LAD/FBD/STL editor.
• For every block flagged as "rewritten" or "incomplete", replace by a manual S7 equivalent or by a block from the STEP 7 standard library.
• Rebuild the symbol table; some S5 symbols (8-char max, no special characters) are lost or truncated.
• Cross-check timer/counter semantics: S5 BCD-coded timers must be re-coded as IEC timers in S7.

Step 2: STEP 7 V5.5 to TIA Portal Migration

Step 2 migrates the STEP 7 V5.5 project into a TIA Portal project. The TIA migration tool is invoked from inside TIA Portal and accepts .s7p / .s7l archives. The target is always a defined CPU type and firmware version.

2.1 TIA Portal Prerequisites

• TIA Portal V14 or V14 SP1 minimum; V15 / V15.1 / V16+ strongly recommended for new S7-1500 work
• Matching S7-1500 HSP (Hardware Support Package) installed for the target CPU
• STEP 7 V5.5 project must be free of warnings and errors before migration

2.2 Migration Procedure

1. In TIA Portal, select Project → Migrate project → S7-300/S7-400 project.
2. Select the STEP 7 V5.5 archive. TIA reports compatibility with the target firmware version.
3. Choose the target S7-1500 CPU and firmware version. The migration tool warns if the S7-1500 firmware is too new or too old for the block set.
4. Review the migration log. "Block has not been migrated" messages must be investigated — these are blocks the TIA tool could not convert and which must be re-implemented.
5. Re-compile, download to PLCSIM, and verify on a test rig before site deployment.

TIA Portal Version Stability Reference

TIA Portal version selection has a direct effect on migration success. The version history below records the typical stability profile observed in the field for S5-to-S7 migration projects targeting S7-1500.

Field engineers report that TIA Portal stability did not reach a level they could "recommend with a good conscience" until V14 SP1, and that even then the TIA platform as a whole was not on par with STEP 7 V5.5 for risk-averse brownfield work. This is a recurring comment across multiple TIA versions (V10 through V13), and the V14 release did not immediately resolve the underlying stability complaints. New TIA architecture changes can make first-time problems worst before service packs stabilize the platform.

S7-1200 Migration Limitation

There is no automatic migration tool from S5 to S7-1200. This is an explicit gap in the Siemens migration offering. The S7-1200 was positioned as a small-machine / cost-optimized controller and was not part of the S5-to-S7 converter strategy.

For S7-1200 targets, the migration must be performed by manual rewrite:

1. Reverse-engineer the S5 program into a function specification.
2. Redesign in TIA Portal using S7-1200-compatible blocks: IEC_Timer (TP, TON, TOF), IEC_Counter (CTU, CTD, CTUD), and the S7-1200 process image model.
3. Re-implement the S5 FBs as TIA Portal FBs or as S7-1200 standard library calls.
4. Test the S7-1200 program against the S5 program on a parallel rig for verification.

Common Migration Issues and Workarounds

Verification and Commissioning Checklist

1. Cross-reference: Generate a fresh cross-reference in STEP 7 V5.5 / TIA Portal and compare it to the S5 source cross-reference. Any unexplained delta is a lost address or symbol.
2. Block consistency: Run Edit → Check Block Consistency in TIA Portal. Resolve every error before download.
3. Simulation: Run the converted program in PLCSIM (S7-300/400) or PLCSIM Advanced (S7-1500). Force I/O and compare behavior to the S5 simulation if available.
4. Online test on the real CPU: With the S5 PLC still running in parallel, force each output on the S7 side and verify field behavior. Then invert: force on the S5 and verify the S7 reads the right input.
5. Communication test: For each migrated CP, verify the partner device sees the S7 with the same identity and slot as the S5 had. DP slave GSD must match; PROFINET device name must match.
6. HMI tag refresh: Cycle every HMI tag at runtime. Any tag that does not update is either a symbol mismatch or a tag-prefix error.
7. Watch-dog / scan-time check: The S7-1500 OB1 cycle time is typically lower than the S5 OB1 cycle time. Verify the S7 program does not break a time-of-day-based logic that relied on the S5's slower scan.
8. Documentation: Export the TIA project, the STEP 7 V5.5 archive, and the original S5 program. Store on a project-server with version tagging.

FAQ