User`s guide

Using the Agilent VEE Development Environment Chapter 1
VEE User’s Guide 65
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.
The rules of data flow in a VEE program are:
• 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.
• All of the data input pins in an object must be
connected. Otherwise, an error occurs when the program
runs.
• An object will not execute until all of its data input pins
have received new data.
• 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.
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.