Rockwell-automation 1771-DB Basic Module User Manual - Series A Manual de usuario descargar pdf (Pagina 40)

Operating Functions

Chapter 5

5–3

A constant is a real number that ranges from +1E–127 to +.9999999

9E+127. A constant can be an integer. We refer to constants as: [const]

An operator performs a predefined operation on variables and/or

constants. Operators require either one or two operands. Typical two

operand or dyadic operators include ADD (+), SUBTRACT (–),

MULTIPLY (*) and DIVIDE(/). We call operators that require only

one operand, unary operators. Some typical unary operators are SIN,

COS and ABS.

A variable can be:

a letter (e.g. A, X,I)

a letter followed by a one dimensioned expression, (e.g. J(4), GA(A +

6), I(10*SIN(X))

a letter followed by a number followed by a one dimensioned

expression (e.g. A1(8), P7(10*SIN(X)), W8(A + B).

a letter followed by a number or letter (e.g. AA, AC, XX, A1, X3,

G8) except for the following combinations: CR, DO, lE, IF, IP,

ON, PI, SP, TO, UI and UO.

We refer to variables that include a one dimensioned expression [expr] as

dimensioned or arrayed variables. We refer to variables that contain a

letter or a letter and a number as scalar variables. Any variables entered

in lower case are changed to upper case. We refer to variables as:

[var].

The BASIC module allocates variables in a “static” manner. This

means that the first time a variable is used, BASIC allocates a portion

of memory (8 bytes) specifically for that variable. This memory cannot

be de-allocated on a variable to variable basis. This means that if you

execute a statement (e.g. Q 3), you cannot tell BASIC that the

variable Q no longer exists to “free up” the 8 bytes of memory that

belong to Q. You can clear the memory allocated to variables by

executing a CLEAR statement. The CLEAR statement “frees” all

memory allocated to variables.

5.2.6

Constants

5.2.7

Operators

5.2.8

Variables

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Rockwell-automation 1771-DB Basic Module User Manual - Series A Manual de usuario Pagina 40