150 Chapter 3
Easy Ways to Control Instruments
Using Direct I/O
Sending an Expression List to an Instrument
In some cases, you may want to send an expression list to an instrument. For
example, you may want to loop through a number of frequencies in the
Function Generator. To do so using a Direct I/O Transaction, you would
use a variable for the frequency in an expression list, and add a data input for
that variable to the Direct I/O object. The following steps describe how to
send an expression list to an instrument.
1. Place a second
Direct I/O object for the HP3325B in the Main
window. Double-click in the transaction area to get the
I/O
Transaction
dialog box.
You can use all of the defaults except for the command string. In this
case, use the format
"FR", <frequency>, "HZ". This is an Expression
List, each expression being separated by commas. The frequency is
represented by variable
A, which will be a data input to the Direct I/O
object.
2. Click on the input field for command strings and type
"FR",A,"HZ".
(For example, if
A were 100, VEE would send the string "FR100HZ".)
Click
OK. Notice that VEE automatically adds a data input pin labeled A.
3. Select
Flow ⇒ Repeat ⇒ For Range and place it to the left of the
Direct I/O object.
4. Connect the
For Range data output pin to the Direct I/O data input
pin.
5. Edit the fields in
For Range to: From 10, Thru 1.8M, and Step 50k.
For Range will now send out numbers ranging from 10 to 1.8 million in
steps of 50,000. As the numbers are received by the Direct I/O object, the
command string causes the function generator to output the frequencies.
The Direct I/O setup should look like Figure 3-19.
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