Applicable Systems
S7-1200
S7-1500
S7-300
S7-400
LOGO!
SINAMICS
Symptoms
The SF LED flashes. The CPU logs a programming error, indicating that a code execution issue was detected during the scan cycle. The CPU may continue running or enter STOP mode depending on severity.
Possible Causes
- Access to a non-existent data block address
- Array index out of bounds in a user program
- Pointer access to an invalid memory area
- Type conversion error in user logic
Troubleshooting Steps
- Step 1: Open the diagnostic buffer and identify the specific code block and network where the error occurred
Locate the exact instruction causing the programming error - Step 2: Open the identified block in TIA Portal and review the logic at the fault point
Identify the invalid memory access or type conversion - Step 3: Fix the programming error by adding bounds checking or correcting the pointer logic
Code executes without errors on the next scan - Step 4: Download the corrected block and monitor for recurrence
No new programming errors appear in the diagnostic buffer
How to Reset
To reset: 1) Correct the programming error in TIA Portal. 2) Download the updated block to the CPU. 3) If the CPU is in STOP mode, switch it to RUN mode. 4) Clear the diagnostic buffer. Caution: Programming errors can cause unpredictable behavior, so verify the fix thoroughly before returning to RUN.
Frequently Asked Questions
- Q: How do I find which code block caused the programming error?
The diagnostic buffer in TIA Portal will list the specific block number and network where the error was detected.
- Q: Will a programming error always stop the CPU?
Not always. Minor errors may be handled by the error OB, but critical errors such as invalid memory access will force the CPU into STOP mode.
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Source: Siemens S7-1500 System Manual, Edition 08/2023
Category: PLC & VFD
Published: 2026-10-17
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