Resolving STEP 7 Source File Compile Errors: German Mnemonics

Problem Overview

When a STEP 7 V5.x source file (STL, LAD, or FBD) is downloaded from a Siemens Support entry, a third-party repository, or a peer-shared archive, it frequently fails to compile in the receiving engineer's SIMATIC Manager. The output window shows red entries on every network, and the Save and Compile operation halts before any blocks are generated. In the majority of cases, the root cause is not parameter corruption, missing hardware, or library version mismatch — it is a mnemonic-set mismatch between the exported source and the installed SIMATIC Manager editor language.

STEP 7 supports two mnemonic conventions for STL/LAD/FBD code generation: the IEC-conformant English mnemonics (A, AN, O, ON, =, L, T) and the legacy German mnemonics (U, UN, O, ON, =, L, T). The convention used to compile and display the program is bound to the SIMATIC Manager UI language setting, not to the project properties. When the file was generated on a German-locale workstation and is opened on an English-locale workstation, every instruction in the source becomes a syntax error at compile time. Data block (DB) parameter errors are a secondary symptom: the editor cannot resolve referenced DBs because it never finished parsing the network header.

The error window typically reports a mix of Unknown instruction and DB not found entries. The first error almost always points to a bit-logic or timer token in network 1; the remaining errors cascade from that failure.

Root Cause: German vs English Mnemonics

STEP 7 V5.x stores STL source code as ASCII text. The exporter writes either the German or English form of every instruction, depending on the locale of the exporting SIMATIC Manager. The two conventions are not interchangeable — there is no internal marker that tells the importer "this is German, please transliterate." The compiler expects the literal token it knows about (its own mnemonics) and rejects everything else.

The mismatch is most common in three scenarios:

1. A source file is downloaded from a German-language Siemens Support entry (support.industry.siemens.com) that was created on a German-locale system.
2. An engineer copies STL snippets from German-language training material, Siemens FAQs, or peer-shared archives.
3. A project is migrated from a German-locale STEP 7 V5.5 system to an English-locale STEP 7 V5.7 system without re-exporting the source.

The reported errors will be of the form Unknown instruction 'U' at network 1, Syntax error before 'AUF', or Invalid operand for 'SE'. The errors cascade, so resolving the first line in network 1 often eliminates dozens of downstream errors at once. DB and timer parameter errors are not real defects in the logic — they are symptoms of the parser failing to reach the operand section of the instruction.

For a complete reference on the mnemonic conventions, see the STEP 7 V5.7 programming manual available at the Siemens Industry Online Support portal.

Solution Path 1: Switch SIMATIC Manager Language to German

The fastest path to a working compile is to align the SIMATIC Manager language with the source file's origin. Use this method when the source is known to be German, when you do not need to maintain an English-mnemonic project, or when you must validate the source's behavior on a German-locale system as the original author intended.

1. Close all open projects in SIMATIC Manager.
2. Open the menu Options > Customize.
3. Navigate to the Language tab.
4. From the Mnemonics dropdown, select German.
5. Click OK and restart SIMATIC Manager.
6. Reopen the project and recompile.

This change affects only the current Windows user profile. Other users on the same workstation keep their own language settings. The STEP 7 installation media (per the Siemens Industry Online Support readme) ships with both language packs, so no additional install is required to toggle.

Solution Path 2: Convert German Mnemonics to English

When the project must remain on English mnemonics (for example, because it is part of a multi-engineer team that standardizes on IEC English, or because the target TIA Portal environment requires English sources), convert the imported source to English mnemonics before compiling. The conversion is a textual replacement operation on the STL file, but it must be done carefully to avoid altering identifiers, comments, or symbol names that happen to contain the letters U, O, X, S, R, L, T.

Procedure

1. Open the source file in a plain-text editor that supports regular expressions (Notepad++, Visual Studio Code, UltraEdit).
2. Disable word-wrap and show whitespace so column boundaries are visible.
3. Apply the case-sensitive replacements in the table below, scoped to the start of an instruction token (delimited by whitespace, newline, or a parenthesis). Do not use a naive Find/Replace on the whole document — this will corrupt symbol names such as U_MOTOR_ON or SE_PRESSURE_OK.
4. Save the file with ANSI or UTF-8 (no BOM) encoding. STEP 7 STL source files are ASCII / ANSI; a UTF-8 BOM will be parsed as a stray instruction and the file will not open.
5. Reopen the project in SIMATIC Manager and recompile.

A regex pattern that constrains replacement to a leading-token position looks like: (^|[\s(])U(\s|$) → \1A\2. The same pattern is applied for each entry in the conversion table below. The leading and trailing capture groups preserve the surrounding whitespace and parentheses so the network structure is not disturbed.

German-to-English Mnemonic Conversion Table

Operators that are identical in both mnemonic sets and require no replacement: ==, <>, >, <, >=, <=, +, -, *, /, MOD (arithmetic and comparison), SLW, SRW, SLD, SRD (shift), RLD, RRD (rotate), AW, OW, XOW (word logic), ITD, DTI, ITB, BTI, DTB, BTD, DTR (convert), TAK, NOP 0, NOP 1, SET, CLR (accumulator / stack). The S5TIME preset literal syntax S5T#<value><unit> is also identical in both locales.

Resolving Data Block (DB) Parameter Errors

When the editor rejects the first instruction in network 1, it cannot construct the address list, so all subsequent DB references in the same network are reported as "DB not found" or "Invalid DB number." This produces a cascade of errors that disappear as soon as the mnemonic language is corrected. If DB errors persist after the mnemonic correction, address them with the following checks:

1. Verify that the referenced DB exists in the S7 Program > Blocks container. Downloaded STL source often references DBs from a separate source file (DB10, DB11, ...) that must be imported alongside it.
2. Check the DB number. German and English systems both use the same DB numbering (DB1, DB2, ... DB32767). No transliteration is required for the number itself.
3. For instance DBs (DI), confirm that the parent FB is present and compiled. The instance DB is auto-generated only when the parent FB compiles cleanly.
4. For system data blocks (SDB), confirm the matching hardware configuration has been built. SDBs are generated by HW Config, not by the STL compiler, and will be empty if HW Config was never run for the project.
5. For shared DBs that use UDTs (user-defined data types), import the UDT source before the DB source. Otherwise the DB will compile with placeholder types and produce warnings on every structure member.

The "time" parameter mentioned in the original error report refers to the time base (TB) and preset value (TV) fields of an IEC timer block. In STL, these are loaded into the timer word before the timer call:

      L     S5T#5S          // preset, identical in both locales
      SD    T1              // English: SD (on-delay)
      SE    T1              // German: SE (on-delay)

The timer preset uses S5TIME format in both locales: S5T#<value><unit> where unit is MS, S, M, or H. The value must be an integer, and the time-base resolution is set automatically by the editor (10 ms, 100 ms, 1 s, or 10 s). No transliteration is needed for the time value itself.

Bit memory (M), process image (I/Q), and peripheral (PI/PQ) addresses are identical in both locales. Symbol names imported from a German project must be kept in their original case — German systems permit umlauts in symbol names (e.g., Schütz_EIN), but English systems may not display them correctly. Replace umlauts with their ASCII equivalents (ä→ae, ö→oe, ü→ue, ß→ss) and update the symbol table to match before re-compiling.

OP177B Compatibility and Online/Offline Monitoring

The original problem statement refers to monitoring whether an OP (Operator Panel) is online or offline. The OP177B is a 5.7" STN panel from the SIMATIC HMI product line, designed for S7-200 / S7-300 / S7-400 integration via MPI / PROFIBUS at 187.5 kbit/s to 12 Mbit/s. Online/offline status in STEP 7 is reported through the PG/PC interface and the CP (communications processor) state.

To monitor OP online status from a STEP 7 program, the standard approach uses the system function SFC51 (SZL — System State List) to read the module status of the OP's MPI/PROFIBUS node. SFC51 calls are mnemonic-agnostic (the function name and parameter list are identical in both locales), but the surrounding STL wrapper code must be in the correct mnemonic set.

      CALL  "SFC51"        // English CALL / German CALL (same)
       SZL_ID  := W#16#0111 // Local bus, module status list
       RET_VAL := MW100
       BUSY    := M101.0
       SZL_HEADER := MW102
       SZL_PTR   := P#M110 BYTE 20

The resulting SZL contains one 32-byte entry per accessible node. A non-zero entry in byte 0 indicates the OP is reachable. A zero entry indicates the OP is offline, disconnected, or its PROFIBUS segment is down. The OP177B-specific parameter blocks (built in WinCC flexible 2008 SP5 or later) compile to a set of SDBs and a connection block. These are loaded via Set PG/PC Interface > PC Adapter (MPI) > Properties and transferred with the PLC > Download to Target System menu in SIMATIC Manager.

For OP177B configuration manuals and firmware notes, see the Siemens Industry Online Support entry list filtered by product "OP177B."

Verification Procedure

After applying either solution path, verify the compile result and program behavior with the following sequence:

1. In SIMATIC Manager, right-click the Blocks folder and select Compile. Confirm that the output window reports zero errors and zero warnings.
2. Open the System Data (SDB) container. Confirm that HW Config has been run at least once for the project; otherwise the SDBs are empty and the CPU will reject the download.
3. Perform a consistency check: PLC > Check Block Consistency. This passes only when all referenced blocks (FCs, FBs, DBs, UDTs) compile and their interfaces match.
4. Download to the target CPU. Monitor the CPU diagnostic buffer (PLC > Diagnostic/Setting > Diagnostic Buffer) for any "Block not found" or "Interface error" entries that point back to unresolved cross-references.
5. From the online view, force the OP online / offline transition and verify the SZL read returns the expected non-zero / zero pattern at the output of the monitoring block.
6. Switch each block's view between STL, LAD, and FBD. The view switch forces a re-parse and surfaces any hidden character corruption (for example, German quotation marks "…" that did not survive the text-editor round-trip).

Troubleshooting Matrix

Operational Notes

The mnemonic set is per-workstation, not per-project. The same project file behaves differently on a German-locale PG versus an English-locale PG. For multi-engineer teams, standardize on English mnemonics (IEC) and document this in the project quality plan. The STEP 7 V5.7 release notes confirm that English is the default mnemonic set for new installations.

For migration to TIA Portal, the mnemonic language is no longer a concern: TIA Portal uses IEC 61131-3 English mnemonics exclusively. However, imported S7 sources still carry their original German/English tokens, and the same conversion procedure applies during the "Migrate S7 project" wizard in TIA Portal V17 or later. After migration, run a global find/replace pass on the imported SCL/STL sources to convert any German mnemonics to IEC English, then recompile in the TIA Portal editor.