ControlLogix 5570 Major Fault T04:C16 after program download, what to check?
I'm getting a Major Fault T04:C16 on a ControlLogix 5570 controller after downloading a program. The fault occurs as soon as the routine with the unknown instruction executes. What should I check first?
A Major Fault T04:C16, or 'Unknown Instruction', indicates the controller encountered an instruction it doesn't recognize during program execution. This typically happens after a program download, especially if the project was converted from another platform or firmware revision. The fault-specific information in the MajorFaultRecord and the Major Faults tab will identify the program and routine where the issue occurred.
Likely causes and checks
1Program converted from another controller or platform
- Points to it
- The project was recently migrated from a different controller type (e.g., PLC-5/SLC) or an older Logix revision, which can introduce instructions not recognized by the current controller.
- Check
- Review the conversion report generated during the migration process and search the routines for any instructions that were flagged or noted during conversion.
2Project and controller firmware do not match the instruction set
- Points to it
- The fault started after a firmware change on the controller or a download from a different version of Logix Designer, meaning the instruction set used in the project might not be compatible with the controller's current firmware.
- Check
- Compare the project revision, the controller's firmware version, and the version of Logix Designer used to create or modify the project.
Next check: Start by examining the MajorFaultRecord and the Major Faults tab in the controller's diagnostics to pinpoint the specific program and routine where the unknown instruction is located, rather than searching the entire project.
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