What causes Siemens SINUMERIK alarm 12585?

Attempting to write to a read-only system variable in a synchronous action block. Using standard user variables instead of special variables ($AC_*) in SYNFCT synchronous assignments. Incorrect variable scope - mixing real-time accessible variables with non-real-time variables in motion synchronous context. Variable assignment in WHEN/DO clause that conflicts with real-time synchronous execution requirements.

How do I fix Siemens SINUMERIK alarm 12585?

1. Review the SYNFCT block and identify all variables in the DO clause - verify they are special variables ($AC_*) that support real-time synchronous write access 2. Replace any standard user variables or read-only system variables with appropriate special variables that permit synchronous modification (e.g., use $AC_DRESSER or custom permitted variables instead of $AC_TIME for write operations) 3. Check the NC program syntax - ensure the variable assignment format matches real-time synchronous requirements and variable type declarations 4. Consult the machine tool builder documentation to confirm which special variables are writable in synchronous actions for your specific machine configuration 5. Test the corrected SYNFCT block in dry-run mode to verify the synchronous action executes without alarm recurrence

Siemens SINUMERIK codes

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Siemens SINUMERIK Controller

Servo/Axis · Intermediate · 30-45 minutes

Alarm 12585

Siemens 840D 12585 - Channel block variable cannot be changed synchronously

When assigning SYNFCT in motion synchronous actions and result variables, only special variables are allowed. Real-time synchronous access is allowed here. Example: WHEN $AA_IM[AX1]>= 100 DO $AC_TIME=1000. The variable $AC_TIME (time from beginning of block) cannot be written

Siemens SINUMERIKServo/AxisIntermediate30-45 minutes

12585

Siemens 840D 12585 - Channel block variable cannot be changed synchronously

Channel block variable cannot be changed synchronously

Safety

Refer to Siemens documentation
Ensure qualified technician performs repairs

Common Causes

Attempting to write to a read-only system variable in a synchronous action block
Using standard user variables instead of special variables ($AC_*) in SYNFCT synchronous assignments
Incorrect variable scope - mixing real-time accessible variables with non-real-time variables in motion synchronous context
Variable assignment in WHEN/DO clause that conflicts with real-time synchronous execution requirements

Troubleshooting Steps

1Review the SYNFCT block and identify all variables in the DO clause - verify they are special variables ($AC_*) that support real-time synchronous write access
2Replace any standard user variables or read-only system variables with appropriate special variables that permit synchronous modification (e.g., use $AC_DRESSER or custom permitted variables instead of $AC_TIME for write operations)
3Check the NC program syntax - ensure the variable assignment format matches real-time synchronous requirements and variable type declarations
4Consult the machine tool builder documentation to confirm which special variables are writable in synchronous actions for your specific machine configuration
5Test the corrected SYNFCT block in dry-run mode to verify the synchronous action executes without alarm recurrence

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