Troubleshoot the 64 KB FC Compile Limit in PCS 7 V8.2 on CPU 416-5H
On a CPU 416-5H, Siemens specifies a maximum function size of 64 KByte, so a CFC compile error naming an FC at that size is a code-area limit rather than a direct count of redundant I/O cards. The discussion reports PCS 7 V8.2 and FC767 after redundancy was enabled on the twenty-second card, but supplies no compile log or confirmed fix. Diagnose the generated function and runtime group before changing the project; the available evidence cannot establish a universal maximum number of redundant cards.
Table of Contents
- What the 64 KB message means
- Diagnose the oversized generated function
- Why a card-count answer cannot be given
- Verification
- Limitations and Operational Precautions
- Engineer FAQ
- Technical References
- Related Articles
- Related Tags
What the 64 KB message means
The reported “Maximum length of code area reached” message is a compile-time code-size limit, not by itself a maximum count of redundant I/O cards. Siemens' S7-400H instruction list specifies a maximum size of 64 KByte for an FC on CPU 416-5H. The ticket reports PCS 7 V8.2, a 416-5H, and an FC767 compile failure after enabling redundancy on the twenty-second card, but the thread was closed as a duplicate without a confirmed diagnosis or resolution.
The number of cards that can be configured depends on the resulting generated program and project configuration. This evidence does not establish a fixed maximum number of RED signals or cards for this project. Do not treat “21 cards compiled” as a supported limit or assume a specific card type caused the error.
Diagnose the oversized generated function
Use the PCS 7 compilation results to identify the generated function and runtime group associated with the error. The source names FC767 but does not include the full diagnostic, compile log, generated SCL, hardware configuration, module types, or the generated driver mapping. Preserve those details before changing the project.
- Save a project backup and retain the failed compilation log.
- Check the exact compile message and determine whether FC767 itself is reported as exceeding the maximum size. Confirm whether it is an automatically generated driver/runtime-group function or a user-created function before editing anything.
- Review the generated code and the runtime group or OB associated with that function. Identify which block calls or generated driver content contribute to its size; do not infer that the twenty-second card alone is the cause.
- Compare the project's PCS 7 V8.2 and hardware configuration with documentation for the installed module-driver and redundancy configuration. The available ticket does not list the I/O modules, firmware, or driver package.
- Where applicable to the identified oversized CFC runtime group, Siemens' PCS 7 Compendium guidance describes reducing a block near the 64 KB limit by inserting additional runtime groups or moving blocks/runtime groups to another cyclic interrupt. Any such restructuring must preserve task timing, block dependencies, driver behavior, and project-specific safety requirements.
- Recompile and inspect the result before considering any download. A successful compile only resolves the offline code-size issue; the project still requires the site's normal review and commissioning process.
Why a card-count answer cannot be given
The question asks how many redundant signals or I/O cards the CPU 416-5H can support. The provided evidence addresses the maximum function code size, not a universal redundancy-card count. There is not enough information to calculate the generated code burden from “23 cards”: module types, channel counts, redundancy arrangement, PCS 7 V8.2 update level, module-driver version, process-image/task assignment, and actual compiler diagnostic are absent.
The corresponding Siemens forum discussion describes a similar code-area error in a project with redundant modules and points readers to the PCS 7 FAQ on CFC compilation and the Compendium discussion of runtime-group sizing. That is relevant diagnostic context, not a confirmed resolution for this ticket. A project-specific maximum requires inspecting the generated compile output and the exact configuration.
Verification
After any supported structural change, recompile with the same project and hardware configuration and confirm the compiler no longer reports a code-area overflow for the implicated function. Review warnings and inspect the generated function/runtime-group assignment to confirm the intended logic and driver calls remain present. Validate cycle-time and task assignment impacts in the project before a controlled download; do not use the article's reported card count as an acceptance criterion.
Limitations and Operational Precautions
The source discussion is incomplete and was closed because a duplicate thread existed. No final fix, exact error text, compilation report, module list, CPU order number/firmware, or PCS 7 V8.2 update level is available. The 64 KByte figure is a maximum FC size from Siemens' S7-400H instruction list, not a redundant-I/O capacity rating.
Moving runtime groups or blocks can change execution scheduling and dependencies. Make changes only with a complete project backup and engineering review; validate the affected cyclic tasks and relevant redundancy/driver behavior before downloading to a live AS.
Engineer FAQ
Does CPU 416-5H have a 64 KB function-size limit? Siemens' S7-400H instruction list gives a maximum function size of 64 KByte for CPU 416-5H.
Does the 64 KB limit mean there is a maximum of 21 or 22 redundant cards? No. It limits an individual function's code size; the ticket does not establish a fixed number of cards or redundant signals.
Is FC767 necessarily the oversized generated driver function? The thread says the compilation error appears in FC767, but it does not include the compiler output or generated code needed to determine what that function contains.
What should be checked first? Preserve and inspect the compilation log, identify the exact implicated function and runtime group, and compare the generated code with the project configuration.
Can blocks be moved to another runtime group? Siemens' PCS 7 Compendium describes adding or moving runtime groups for a block approaching 64 KB. Applicability and scheduling effects must be assessed for the specific project and software version.
Technical References
- Siemens, S7-400H Instruction List, 07/2012, A5E01359153-03, “Functions (FC) and Data Blocks.” The table specifies a maximum FC size of 64 KByte for CPU 416-5H: PDF.
- Siemens, PCS 7 Compendium Part A – Configuration Guidelines, V9.0, 03/2018, p. 185. It describes inserting runtime groups or moving blocks/runtime groups to another cyclic interrupt to reduce a block near 64 KB: PDF.
- Siemens Industry Support forum, “Maximum length of code area reached (max. 64 Kbytes),” Topic 134868. A related discussion points to the Siemens CFC compile FAQ and mentions runtime-group code size; the thread is community experience, not a resolution for this configuration: Discussion.