What causes Siemens SINUMERIK alarm 12640?

Mismatched or missing ENDIF statement for an IF-ELSE block. LOOP-ENDLOOP pair not properly closed before another control structure ends. Missing LOOP statement with corresponding ENDLOOP present in code. Control structure nesting order violated (e.g., closing outer loop before inner IF statement). Syntax error in control structure keywords (typos in IF, ELSE, ENDIF, LOOP, ENDLOOP).

How do I fix Siemens SINUMERIK alarm 12640?

1. Review the program at the specified channel and block number to identify the control structure sequence 2. Verify all IF statements have corresponding ENDIF statements and all LOOP statements have corresponding ENDLOOP statements 3. Check nesting order by tracing from innermost to outermost control structures to ensure they close in reverse order of opening 4. Confirm spelling and syntax of all control structure keywords match Siemens 840D/828D documentation (IF-ELSE-ENDIF, LOOP-ENDLOOP) 5. Load a known working program to verify control structure syntax is valid, then compare against the problematic program

Siemens SINUMERIK codes

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Siemens SINUMERIK Controller

Servo/Axis · Intermediate · 15-45 minutes

Alarm 12640

Siemens 840D 12640 - Channel block invalid nesting of control structures

Error in program run: Opened control structures (IF-ELSE-ENDIF, LOOP-ENDLOOP etc.) are not terminated or there is no beginning of loop for the programmed end of loop. Example: LOOP ENDIF ENDLOOP

Siemens SINUMERIKServo/AxisIntermediate15-45 minutes

12640

Siemens 840D 12640 - Channel block invalid nesting of control structures

Channel block invalid nesting of control structures

Error in program run: Opened control structures (IF-ELSE-ENDIF, LOOP-ENDLOOP etc.) are not terminated or there is no beginning of loop for the programmed end of loop. Example: LOOP ENDIF ENDLOOP

Safety

Refer to Siemens documentation
Ensure qualified technician performs repairs

Common Causes

Mismatched or missing ENDIF statement for an IF-ELSE block
LOOP-ENDLOOP pair not properly closed before another control structure ends
Missing LOOP statement with corresponding ENDLOOP present in code
Control structure nesting order violated (e.g., closing outer loop before inner IF statement)
Syntax error in control structure keywords (typos in IF, ELSE, ENDIF, LOOP, ENDLOOP)

Troubleshooting Steps

1Review the program at the specified channel and block number to identify the control structure sequence
2Verify all IF statements have corresponding ENDIF statements and all LOOP statements have corresponding ENDLOOP statements
3Check nesting order by tracing from innermost to outermost control structures to ensure they close in reverse order of opening
4Confirm spelling and syntax of all control structure keywords match Siemens 840D/828D documentation (IF-ELSE-ENDIF, LOOP-ENDLOOP)
5Load a known working program to verify control structure syntax is valid, then compare against the problematic program

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