ISPSoft User Manual *1. In the table above, the default value of M0 is FALSE, the default value of M1 is TRUE, and the default value of D0 is 5. *2. The operands for an exponentiation operator must be constants or floating-point symbols, and must not be devices. 13.1.5 Keyword and Comment In computer programming, a keyword is a word which has a special meaning to the programming language. For example, TRUE and FALSE in a program represent Boolean values, and the IF statements in the example above represent tasks which will be executed. Besides, applied instructions are regarded as keywords.
In order to prevent a program from being compiled incorrectly, the words which are regarded as keywords in the program cannot be declared to be symbols. However, the words which are regarded as keywords in a program can be parts of the symbols in the program. For example, “ FIFO ” and “ _IF ” are allowed. In a structured text, you can use multiple comments (using words between (* and *) , (/* and */) and single line comment (using (/ /) ). When a program is compiled, the system automatically skips the words between (* and *) , (/* and */) and (/ /) in the program. As long as the structure of a structured text is not destroyed, comments can be put anywhere in the structured text.
However, users have to be careful about the readability of the structured text. Please refer to the examples below. The comments in the left example are legal. The comment in the right example divides the keyword “END_IF” into two parts by using /*and*/, and therefore an error will occur after the program is compiled.
13-6 Symbol Function Data format Example of an Precedence expression Operand Result of an Expression Value operation (Value of an expression) =, Equal to, not equal to Any value Boolean value D0 2 TRUE Boolean value M0 = TRUE FALSE AND, & Logical AND operation Boolean value Boolean value M0 & M1 FALSE XOR Logical exclusive OR operation Boolean value Boolean value M0 XOR M1 TRUE OR Logical inclusive OR operation Boolean value Boolean value M0 OR M1 TRUE Lowest