Programming

Each controller has the capability to carry out automated tasks. These tasks are described by a program or script. A script is essentially a set of instructions. Programs must follow the specific script syntax. This section gives an overview of programming along with several examples. The examples are arranged in increasing complexity. It is recommended that you review these examples in sequence.

The section “Using Parameters and Variables” gives useful insights into the effective use of iNetGrow through the System View dialog or through a web browser (see the section “Integrating with Web Services”).

Overview

Programs consist of a set of instructions. Ultimately, these instructions compute the values of the outputs from the values of the inputs. Thus, the program allows the implementation of virtually an endless number of automated tasks.

The iNetGrow script contains five types of variables: inputs, outputs, variables, and parameters, and system variables. Inputs and outputs are the user-given names for the various signals that are available at the modules. Refer to the sections “Configuring I/O Modules” and “Named Variables” for more information about naming the inputs and outputs. Variables and parameters are general-purpose memory values. Parameters are stored in non-volatile RAM. Hence, parameters retain their values even if the power to the controller is interrupted. System variables are values maintained by the controller to carry out its tasks. System variables start with the underscore character (‘_’). For example, “_second” is the value kept by the system clock. Its value is the current seconds. All variables are 16-bit signed integers.

The program has two sections: definitions and statements. The definitions list all the variables used in the program (excluding the system variables). The statements comprise the “business end” of the program. These are the instructions the controller follows when computing the outputs from the inputs. The simplest statement is an assignment statement, with the familiar syntax,

output = expression;

As in C or JAVA, statements are terminated by a semicolon character. An expression is a quantity dependent on one or more variables. Expressions may contain many terms. For example,

output = input/2;

Refer to the section “Script Syntax” for the various operators allowed by iNetGrow. It is important to note that no operator precedence is assumed. You must explicitly indicate the precedence by using parantheses. For example,

output = a/b+c;

Is not allowed. Instead, use

output = (a/b)+c;

output = a/(b+c);

You may combine one or more statements by curly brackets to make compound statements. For example,

{ x=1; y=1; }

A condition is an expression, whose value is evaluated to be zero or one. Conditional statements use such expressions in the familiar syntax. Note that the action for the conditional statement is a compound statement.

if(a<b) { x=1; y=1; }

The “else” clause is also supported.

if(a>=b) { x=1; } else {x=2; }

It should be noted that white spaces (blanks, tabs, new line characters) are ignored by iNetGrow. This allows you to format your script in a more organized fashion. For example,

if(a!=b)

{

x=1;

y=1;

}

else

{

x=2;

y=2;

}

The iNetGrow script does not support loops or arrays.

The following examples are arranged in increasing complexity.