Siemens TIA Portal / SIMATIC S7

Versions (as of 2026-09)

• TIA Portal V21 was announced on 2025-11-11. V20 had reached Update 5 by 03/2026.
• SIMATIC SD (.s7dcl/.s7res) is the new Git-friendly text format:
  • LAD, UDT and DB from V20 Update 3.
  • SCL, FBD, F-FBD, F-DB and mixed blocks from V20 Update 4.
  • V21 extends it further.
  • It does not support STL.
• SIMATIC AX is a VS Code-based ST toolchain with apax, OOP and unit tests. It is "Early Access for selected productive use cases". AX ST is not SCL.

Always ask for the exact TIA version and the CPU family, for example "S7-1500, V20 Upd 4". Formats, namespaces and the available instructions all depend on them.

Choosing the deliverable

Full format detail, the namespace-version table and the SCL-vs-IEC differences are in references/simaticml-and-sources.md.

SCL rules you must follow

• Locals and globals:
  • Inside code, locals take # (#start). Declarations do not.
  • Global symbols are double-quoted: "DB_Line".speed, "FC_Scale"(…).
• Structure: code follows BEGIN. Blocks end with END_FUNCTION_BLOCK, END_FUNCTION, END_DATA_BLOCK or END_TYPE. REGION … END_REGION groups code.
• Timers:
  • Prefer multi-instances in the FB's static area: tonX : TON_TIME;, called as #tonX(IN := …, PT := …);. An IEC_TIMER variable is called as #t.TON(…).
  • Call them every cycle and gate IN (validator rules ST030–ST033 understand #inst( and #inst.TON().
• Optimized access ({ S7_Optimized_Access := 'TRUE' }) is the default on S7-1200 and S7-1500. Do not rely on absolute offsets into optimized DBs.
• Enums: classic S7 has no IEC enums. Use named constants (a local or global constant) or an Int state with documented values.

Traps that cost the most on site

1. An FB interface change re-initialises its instance DBs on download. Setpoints and counters go back to their start values. Plan for download without reinitialization (memory reserve), or, on V21 with S7-1500 FW 4.1, "Keep actual values". Otherwise back up actual values first.
2. Array index out of range: the S7-1500 goes to STOP unless OB121 or local GET_ERROR handles it, while the S7-1200 stays in RUN. ENO is not cleared, so check indices explicitly.
3. Cycle overrun: OB80 is called. The CPU stops if OB80 is missing, or on a second overrun in the same cycle.
4. Temps: in standard blocks they are undefined until written. Write before you read.
5. In SCL, "Set ENO automatically" is off by default. Programming and I/O access errors never reach ENO.
6. Forces survive going offline, and only peripheral I/O can be forced.
7. Modbus TCP server: register 0 is the first word of MB_HOLD_REG, which clients call 40001. Each connection needs its own instance DB and ID.
8. PUT/GET has to be explicitly permitted, and it has no security of its own.
9. Safety programs are F-LAD/F-FBD only, with no REAL. Never present generated F-code as validated.

References

• references/platform-and-structure.md: versions, controller families and languages, the OB table, optimized vs standard access, parameter passing, references and arrays, and download impact.
• references/scl-and-data-types.md: SCL syntax beyond IEC, external-source rules, DTL/S5TIME/ANY/VARIANT/HW types, and timers.
• references/simaticml-and-sources.md: the .scl / SD / SimaticML / AX formats and the namespace table.
• references/style-guide.md: style-guide rule IDs (ES, NF, SE, DA, PE…), naming, and the status WORD convention. Paraphrased, for licence reasons.
• references/communication.md: PROFINET, PUT/GET and S7comm-plus, OUC/TCON_IP_v4, Modbus TCP/RTU, the OPC UA server and client with licences, and data consistency.
• references/diagnostics-safety-motion.md: monitoring, force, trace and the diagnostic buffer, GET_ERR_ID, the S7 review checklist, Safety Integrated, MC_*, and PID.

Validate

Run python3 ${CLAUDE_PLUGIN_ROOT}/scripts/plc_validate.py <file>.

None of these is a TIA compile. Tell the user to compile in TIA and to fix what it reports.