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FANUC Controller
Program/G-code · Intermediate · 30-60 minutes
Fanuc Alarm 1120 - ILLEGAL ARGUMENT FORMAT
Alarm 1120 occurs when the macro program contains an ATAN (arctangent) or POW (power) function with invalid argument formats or values. This is a program execution error triggered during macro variable calculation, typically caused by incorrect syntax, out-of-range values, or attempting mathematical operations that are undefined (such as division by zero in ATAN or negative base with fractional exponent in POW).
1120
Fanuc Alarm 1120 - ILLEGAL ARGUMENT FORMAT
SYSTEM ALARM 1120
Fanuc alarm 1120: SYSTEM ALARM 1120. This alarm indicates a fault condition detected by the Fanuc control. Refer to the alarm number and name to identify the specific system or function involved.
Root Cause Summary
Alarm 1120 occurs when the macro program contains an ATAN (arctangent) or POW (power) function with invalid argument formats or values. This is a program execution error triggered during macro variable calculation, typically caused by incorrect syntax, out-of-range values, or attempting mathematical operations that are undefined (such as division by zero in ATAN or negative base with fractional exponent in POW).
Causes and Fixes
- 1
Review the active macro program at the line where alarm occurred. Check PROGRAM > CURRENT PROGRAM screen and note the N-block number displayed when alarm triggered.
- 2
Locate all ATAN function calls in the macro program. Verify syntax is either ATAN[#variable] or ATAN[#variable1]/[#variable2]. Check for proper bracket closure and argument formatting.
- 3
If using two-argument format ATAN[#i]/[#j], verify that variable #j (denominator) is not zero at execution time. Use SYSTEM > CURRENT screen or add temporary DPRNT statements before the ATAN call to display macro variable values (#100-#999 range).
- 4
Correct the program by adding conditional logic to check for zero denominator (IF[#j EQ 0]GOTO...) or verify macro variable calculations preceding the ATAN function assign valid non-zero values.
Call a technician if:
- ·Mathematical coprocessor hardware failure suspected
- ·System parameters 6000-6050 corrupted
- ·Alarm persists with known good macro syntax
Prevention
- Always initialize macro variables before use in mathematical functions
- Implement range checking with IF-THEN logic before ATAN/POW calculations
- Use macro variable monitoring during program development
- Validate all canned cycle parameters for proper numeric format
Common Mistakes
- Using uninitialized macro variables in calculations
- Passing zero or negative values to POW without validation
- Missing decimal points in parameter values
- Confusing string and numeric macro variable types
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