Siemens SINUMERIK codes
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Siemens SINUMERIK Controller

Servo/Axis · Basic · 10-20 minutes

Alarm 12450

Siemens 840D 12450 - Channel block label defined twice

The label of this block already exists. If the NC program is compiled off-line, the entire program is compiled block for block. During this procedure all multiple labels are recognized; this is not always the case with on-line compilation. (Only the actual program run is compiled here, i.e. program

Siemens SINUMERIKServo/AxisBasic10-20 minutes

12450

Siemens 840D 12450 - Channel block label defined twice

Channel block label defined twice

The label of this block already exists. If the NC program is compiled off-line, the entire program is compiled block for block. During this procedure all multiple labels are recognized; this is not always the case with on-line compilation. (Only the actual program run is compiled here, i.e. program

Safety

  • Refer to Siemens documentation
  • Ensure qualified technician performs repairs

Common Causes

  • Duplicate label names used in the same NC program
  • Label accidentally copied during program editing without renaming
  • Multiple blocks assigned the same label identifier in jump or loop structures
  • Program contains both online and offline compiled sections with conflicting labels
  • Incorrect use of label syntax or naming conventions

Troubleshooting Steps

  1. 1Review the NC program source code and identify all label declarations, searching for duplicate label names in the specified channel and block range
  2. 2Compare label names across the entire program file, including any called subprograms or macro files that may be in scope
  3. 3Edit the program to rename duplicate labels with unique identifiers, ensuring labels follow Siemens naming conventions
  4. 4Perform a full offline compilation of the complete NC program to catch all label conflicts before online execution
  5. 5Clear any cached or partially compiled program data and reload the corrected program into the CNC control

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