Applicable Systems
S7-1200
S7-1500
S7-300
S7-400
LOGO!
SINAMICS
Symptoms
The diagnostic buffer has reached its maximum entry count. Older entries are being overwritten. The CPU continues to operate normally with no change to LED status.
Possible Causes
- Large number of recurring diagnostic events filling the buffer
- Network communication errors generating rapid log entries
- I/O channel faults being repeatedly detected and logged
- Cyclic program errors generating continuous diagnostic entries
Troubleshooting Steps
- Step 1: Open the diagnostic buffer in TIA Portal and review the pattern of entries
Identify whether entries are repetitive or varied in nature - Step 2: Filter entries by event type to find the most frequently occurring
Pinpoint the specific subsystem generating the most logs - Step 3: Resolve the underlying issue causing the repeated diagnostic entries
Entry generation rate drops to normal levels - Step 4: Clear the diagnostic buffer after resolving the root cause
Buffer fills at a normal, manageable rate
How to Reset
To reset: Clear the diagnostic buffer in TIA Portal by selecting all entries and deleting them. No power cycle is required. Caution: Clearing the buffer removes the diagnostic history, so document any unresolved entries before clearing.
Frequently Asked Questions
- Q: Should I worry about diagnostic buffer overflow?
It is not immediately dangerous, but it indicates an underlying issue generating excessive diagnostic events that should be investigated.
- Q: How do I prevent the buffer from overflowing again?
Resolve the root cause of the repetitive entries. Once the underlying issue is fixed, the buffer will fill at a normal rate.
Source: Siemens S7-1200 System Manual, Edition 04/2022
Category: PLC & VFD