ISPSoft User Manual When the users edit the POU of the program type, they have to declare the symbol SC, which represents a state code, and the function block instance in the local symbol table. Owing to the fact that there is a precedence mechanism for the control of the tricolor light, an IF statement can be used in the main program. and the result of the operation is sent to the digital output which is specified. After a state code is specified, the function block must be called. The state code is sent to the function block, 13-36