EET 2259 Unit 4
SubVIs
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Read Bishop, Chapter 4.
Lab #4 and Homework #4 due next
week.
Floyd, Digital Fundamentals, 10th ed
Modular Programming
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When writing a complex program, good
programmers divide their programs into
separate parts that can be written and tested
independently, and that can be re-used in
other programs.
In text-based programming languages, these
parts are called subroutines.
In LabVIEW they’re called subVIs.
(Bishop, p. 173)
Floyd, Digital Fundamentals, 10th ed
Hierarchy of VIs
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Your main VI can contain one or more
subVIs.
Each of those subVIs can contain one or
more subVIs.
Each of those subVIs can contain subVIs.
And so on…
Floyd, Digital Fundamentals, 10th ed
A Little Poem
“Great fleas have little fleas upon their backs to
bite 'em,
And little fleas have lesser fleas, and so ad
infinitum.
And the great fleas themselves, in turn, have
greater fleas to go on,
While these again have greater still, and greater
still, and so on.”
Floyd, Digital Fundamentals, 10th ed
Augustus DeMorgan (1806-1871)
Example: E-Mail Notification.vi
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In LabVIEW’s Example Finder, browse
according to Task. Open Networking folder,
then open Internet & Web folder. Then open
E-Mail Notification.vi.
In its block diagram, double-click on SMTP
Email Send Message.vi.
In its block diagram, double-click on SMTP
Email Send Message Charset.vi.
And so on…
Floyd, Digital Fundamentals, 10th ed
Hierarchy Window
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LabVIEW’s VI Hierarchy Window shows
how all of these VIs are related to each
other.
Open the window by using View > VI
Hierarchy in pull-down menus.
(Bishop, p. 196)
Floyd, Digital Fundamentals, 10th ed
Example: E-Mail Notification.vi
Floyd, Digital Fundamentals, 10th ed
A Simpler Example
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Suppose you’re writing a program that lets
the user enter values for x, y, and z, and
then calculates x3 + y3 + z3. Rather than
placing all of the multiply functions to
compute x3, y3, and z3 individually, consider
building a subVI that will cube any number.
Floyd, Digital Fundamentals, 10th ed
Steps in Creating a SubVI
1.
2.
3.
4.
5.
6.
Create the VI.
Create the icon.
Create the connector with the correct
number of input and output terminals.
Assign the connector’s terminals to the VI’s
controls and indicators.
Add a description.
Save the VI.
Floyd, Digital Fundamentals, 10th ed
Icon
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A subVI is represented by an icon on the
block diagram of a VI that uses the subVI.
When a VI’s front panel or block diagram is
open, the VI’s icon appears in the upper right
corner.
The default icon is the LabVIEW logo along
with a number.
(Bishop, p. 177)
Floyd, Digital Fundamentals, 10th ed
Icon Editor
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If you plan to use a VI as a subVI, you
should replace the default icon with a more
informative icon.
Use the icon editor to do this. Right-click on
the icon in the front panel and select Edit
Icon….
(Bishop, p. 177)
Floyd, Digital Fundamentals, 10th ed
Connector
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To use a VI as a subVI, you must assign it a
connector so that you’ll be able to attach
wires to it on the block diagram of a VI that
uses it as a subVI.
The connector contains one terminal for
each of the subVI’s inputs and outputs.
(Bishop, p. 180)
Input terminals
Floyd, Digital Fundamentals, 10th ed
Output terminal
Connector
Creating the Connector
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To create the connector, right-click the icon
in the front panel and select Show
Connector.
You can choose a different connector
pattern by right-clicking the connector and
selecting Patterns.
(Bishop, p. 181)
Floyd, Digital Fundamentals, 10th ed
Assigning Terminals to Controls
and Indicators
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Next, assign terminals on the connector to
your front-panel controls and indicators.
To do this, click on a terminal with the Wiring
tool and then click on the control or indicator
that you want to assign to that terminal.
Always assign terminals on the left to inputs
(controls), and terminals on the right to
outputs (indicators).
(Bishop, p. 183)
Floyd, Digital Fundamentals, 10th ed
Required, Recommended,
Optional Terminals
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You can identify each terminal as being
required, recommended, or optional.
If required terminals are left unwired, then the
VI will not run as a subVI. But it will run when
recommended or optional terminals are left
unwired.
By default, all terminals are recommended.
To change a terminal’s status, right-click the
terminal and select This Connection Is.
(Bishop, p. 185)
Floyd, Digital Fundamentals, 10th ed
Context Help Window
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Information about a subVI appears
automatically in the Context Help window
when you roll the mouse over the subVI’s icon
on a block diagram.
This information includes
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the subVI’s name and icon
the name of each terminal (in bold text if it’s
required, in plain text if it’s recommended, in gray
text if it’s optional)
The subVI’s description, if you added one
(Bishop, p. 184)
Floyd, Digital Fundamentals, 10th ed
Adding a Description
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You should document your VI by adding a
description of what it does.
To do this, choose File > VI Properties… in
the pull-down menus, then select
Documentation from the drop-down box,
and then type your description.
(Bishop, p. 187)
Floyd, Digital Fundamentals, 10th ed
Adding More Detailed Info
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In addition to a description for the entire VI,
you can also add a description for each
control and indicator on the VI’s front panel.
To do this, right-click on the control or
indicator and choose Description and Tip….
Then type a description and a brief tip.
Now when you roll over the object, its
description will appear in the Context Help
window and its tip will appear next to the
object.
(Bishop, p. 188)
Floyd, Digital Fundamentals, 10th ed
Summary: Creating a SubVI
1.
2.
3.
4.
5.
6.
Create the VI.
Create the icon.
Create the connector with the correct
number of input and output terminals.
Assign the connector’s terminals to the VI’s
controls and indicators.
Add a description.
Save the VI.
Floyd, Digital Fundamentals, 10th ed
Using a VI as a SubVI
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After you’ve created and saved a VI, how
do you call it as a subVI inside another
program?
Choose All Functions on the Functions
palette, then choose Select a VI… and
then locate your VI.
(Bishop, p. 188)
Floyd, Digital Fundamentals, 10th ed
SubVI Is a Separate File
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CAUTION: When you save a program that
calls a subVI, the subVI is not saved as
part of that “caller” VI. The two files are
totally distinct.
So if you send someone the caller VI, you
must also send the separate subVI file, or
the person won’t be able to run your
program.
Floyd, Digital Fundamentals, 10th ed