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Check PLC variable definitions

Navigate to Commissioning → PLC → Variables and verify the data types of variables being accessed match the format used in NC program or HMI.

Use PLCM address to verify exact variable format in Step7/TIA Portal

Verify R-parameter assignments

Check if R-parameters are correctly assigned to PLC variables using proper format specifiers (e.g., $A_DBB, $A_DBW, $A_DBD for different data widths).

Incorrect data width access can cause memory corruption

Validate variable access syntax

Review NC program lines containing variable access and ensure format matches PLC variable definition (BOOL, BYTE, WORD, DWORD, REAL).

Test with direct variable access

Use Service → Variables to manually read/write the problematic variable and confirm data type compatibility.

Check HMI variable configuration

Access HMI → Configuration → Variables and verify format settings for variables showing the alarm.

Look for format strings like %d, %f, %x that don't match variable type

Validate display element properties

Check input/output field properties in HMI screens for correct data type assignment and format specification.

Review user variable definitions

Navigate to HMI → User Variables and ensure data types match between definition and usage in screen elements.

Test variable binding

Use HMI Service mode to test variable connections and verify data exchange works without format errors.

Identify problematic system variable

Check alarm detail %1 parameter to identify which system variable is causing the format error.

Common issues with $AC_PARAM, $TC_PARAM accessing with wrong index format

Verify system variable documentation

Reference SINUMERIK Lists manual to confirm correct data type and access format for the specific system variable.

Check array index format

For array-type system variables, ensure index format matches specification (e.g., integer indices, proper range).

Out-of-range indices can cause system instability

Test with Service Variables

Use Diagnostics → Service → Variables to manually access the system variable and confirm proper format.

Perform NCK memory check

Navigate to Diagnostics → NCK → Memory and run memory consistency check to identify corrupted variable areas.

Backup and restore variable definitions

Create archive of current settings, then restore variable definitions from known good backup via Commissioning → Data Backup.

Always create backup before restoration procedures

Clear and redefine problematic variables

Delete and recreate the specific variables causing format errors through PLC or HMI variable configuration.

Perform system restart

Execute controlled NCK restart to reinitialize variable memory structures and clear any temporary corruption.