Chapter 1 67
Using the Agilent VEE Development Environment
How Agilent VEE Programs Work
How Agilent VEE Programs Work
In VEE, the general flow of execution through a program is called
propagation. Propagation through a program is not determined by the
geographic locations of the objects in the program, but rather by the way the
objects are connected. Propagation is primarily determined by data flow,
which, in turn, is determined by how the data input and output pins of the
objects are connected.
Note In other programming languages such as C, BASIC, or Pascal, the order in
which program statements execute is determined by a set of sequence and
selection rules. Generally, statements execute in their order of appearance in
the program unless certain statements cause execution to branch to another
statement or thread of code.
The rules of data flow in a VEE program are as follows:
n Data flows from left to right through an object. This means that on all
objects with data pins, the left data pins are inputs and the right data pins
are outputs.
n All of the data input pins in an object must be connected. Otherwise, an
error occurs when the program runs.
n An object will not execute until all of its data input pins have received
new data.
n An object finishes executing only after all connected and appropriate
data output pins have been activated.
In VEE, you can change the order of execution by using sequence input and
output pins. However, you do not normally need to use sequence pins except
for special cases. It is generally best to avoid using the sequence pins. If
possible, let data flow control the execution of the program.
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