Rockwell Automation 1771-DB Basic Module User Manual - Series A - Manual (Page 41)

Operating Functions
Chapter 5
5–4
Important: The BASIC Module requires less time to find a scalar
variable because there is no expression
to evaluate. If you want to run a
program as
fast as possible, use dimensioned variables only when
necessary. Use scalars
for intermediate variables and assign the final
result to a dimensioned
variable. Also, put the most frequently used
variables
first. Variables defined first require the least amount of time
to locate.
An expression
is a logical mathematical expression that involves
operators (both unary and dyadic),
constants and variables. Expressions
are simple or complex, (e.g. 12*EXP(A)/100, H(1)
+ 55, or
(SIN(A)*SIN(A)+COS(A)* COS(A)/2).
A “stand alone” variable [var]
or constant [const] is also considered an expression. We refer
to
expressions as:
[expr].
Relational
expressions involve the operators EQUAL (=), NOT
EQUAL (
tu), GREATER THAN OR EQUAL TO (u=), and
LESS THAN OR
EQUAL TO (t=). You use them in control statements
to test a condition
(i.e. IF A t100 THEN...). Relational expressions
always require two operands.
We refer to relational expressions as:
[rel expr].
The system control values include
the following:
LEN (returns the length of your program).
MTOP (the last memory location assigned to BASIC).
See the following
Section 5.6.2 titled, “System Control Values” for
more information.
5.2.8
Variables (continued)
5.2.9
Expressions
5.2.10
Relational Expressions
5.2.11
System Control Values