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Siemens SINUMERIK Controller
Program/G-code · Intermediate · 30-120 minutes
Siemens 840D 100102 - Buffer limit for selection reached
SIEMENS alarm 100102 'Buffer limit for selection reached' occurs when the servo system's internal selection buffer overflows due to excessive axis selection commands or insufficient processing capacity. This typically happens during rapid axis switching operations or when the servo control loop cannot keep up with the command frequency.
100102
Siemens 840D 100102 - Buffer limit for selection reached
Buffer limit for selection reached
Siemens SINUMERIK operator message 100102: Buffer limit for selection reached. This is an informational message from the SINUMERIK control indicating a system status or operation result that may require operator action.
Root Cause Summary
SIEMENS alarm 100102 'Buffer limit for selection reached' occurs when the servo system's internal selection buffer overflows due to excessive axis selection commands or insufficient processing capacity. This typically happens during rapid axis switching operations or when the servo control loop cannot keep up with the command frequency.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Check NC program for rapid axis switches
Review the active NC program around the alarm occurrence for frequent G-code axis selection changes or rapid M-code axis switching commands.
Look for loops with axis selection commands that execute faster than 10ms intervals
- 2
Verify servo cycle time settings
Access HMI > Commissioning > Drive > Servo and check MD1020 (servo cycle time) - ensure it's appropriate for your axis configuration.
Standard servo cycle time should be 2ms or 4ms depending on system complexity
- 3
Optimize NC program structure
Modify the NC program to reduce axis selection frequency by grouping operations or adding brief dwell times (G04) between rapid axis changes.
Always backup the original NC program before modifications
Call a technician if:
- ·Buffer size increases don't resolve the issue
- ·Communication errors persist after parameter adjustments
- ·Alarm occurs with simple single-axis movements
Prevention
- Monitor servo buffer utilization regularly through diagnostics
- Avoid rapid axis selection changes in NC programs
- Maintain proper servo cycle time ratios
Common Mistakes
- Setting buffer size too high initially
- Ignoring communication timing relationships
- Not considering interpolation load when adding axes
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