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Remote Operation
Summary for Experienced GPIB Programmers
Normalization
The WDCA measures insertion loss relative to a normalization done with a
through connection. The normalization can be taken over a broad span and
interpolated back to smaller spans. Use SENSe:NORMalize:WAVelength STARt
and STOP to set normalization span, INITiate:NORMalize to perform norm-
laization.
EOI required
Before sending remote commands to the instrument, set your GPIB interface
to assert the GPIB END message (also called EOI) with the last character of the
transmission. There is a separate GPIB signal line dedicated to EOI, and when
the WDCA sees the EOI, it closes the buffer and begins processing the com-
mands. The WDCA will not accept any more commands until it has parsed and
launched (but not necessarily completed) all the commands in the buffer.
Most interfaces use EOI by default. If, for example, you are using a National
Instruments GPIB card with Visual C or Visual Basic, EOI is probably on. Simi-
larly, if you are using an Agilent GPIB card in a HP-UX workstation, program-
ming in C or C++, EOI is probably on. If you are using HP Basic for Windows,
you will need to enable EOI each time you open a session to the instrument.
This is done using the ASSIGN @WDCA key words, and associating the END key-
word with the session.
Use device clear
The WDCA uses the Selected Device Clear interface message to free the
instrument from error conditions. Clearing the instrument at the start of any
control application will avoid confusing the instrument. You may find it useful
to write a small program that does nothing but clear the instrument, so you
can clear it when you need to as you debug your application.
Note that Selected Device Clear is not a text message like *CLS. It is an inter-
face level command. For VISA, use viClear(). For NI 488.2, use ibclr(). For HP
SICL, use iclear(). For HP Basic for windows, use CLEAR 723 or CLEAR @WDCA.
Use single sweep mode
When using remote programming, you will want the instrument to take a
sweep only after it is set up and you want the sweep to occur. Allowing the
instrument to sweep while you are sending commands significantly slows the
instrument down. In general, unless an operator is tuning a device, it is best to
turn continuous sweep off with:
INITiate:CONTinuous OFF
The instrument defaults to continuous sweep off.
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