Specifications

App-8
Appendix 2 Character Strings that cannot be Used in Label Names and Data Names
Table App. 2-1 Character strings that cannot be used for label names and data names (3/3)
(1) Precautions on using labels
• In a function, the same name as the function cannot be used for a label.
• A space cannot be used.
• A numeral cannot be used at the beginning of label name.
• A label name is not case-sensitive. An error may occur at compilation when the same
label names with different cases (example: 'AAA' and 'aaa') are declared.
• In structured ladder/FBD and ST programs, the same label name can be used for a global
label and a local label by setting the following option in GX Works2
*1
.
*1: Check the "Use the same label name in global label and local label" item under [Tool]  [Options] 
"Compile"  "Basic Setting".
• An underscore (_) cannot be used at the beginning or end of label name.
Consecutive underscores (_) cannot be used for data name and label name.
• For Simple projects, function names and function block names in common instructions
and application functions can be used.
Category Character string
String that starts with K1
to K8
Such as K1AAA

*1
Address Such as %IX0
Statement in ladder
language
;FB BLK START, ;FB START, ;FB END, ;FB BLK END, ;FB IN, ;FB
OUT, ;FB_NAME;,INSTANCE_NAME,
;FB, ;INSTANCE
Common instruction Such as MOV

*3
Windows reserved word
COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8,
COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8,
LPT9, AUX, CON, PRN, NUL
: Applicable,
: With restrictions, : Not applicable
*1: Functions cannot be used.
*3: Applicable for Simple projects without labels only.
1
2 3 4 5 6 7
8
9