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Sweep Mode
The WDCA employs a tunable laser with fixed sweep rates. The faster the
laser sweeps, the more uncertain the wavelength is and noisier the amplitude
is. The instrument provides three sweep modes: Precision, Normal, and Fast.
Use the fastest mode that will meet your accuracy requirements. Refer to
"[:SENSe]:SWEep:SPEed PRECision|NORMal|FAST|0|1|2" on page 6-86.
Command synchronization
The WDCA may start executing the next command before finishing the previ-
ous one. This is common among GPIB controlled instruments - it allows the
instrument's multi-tasking operating system to execute commands as quickly
as possible. Because of this, you will need to use *OPC, *OPC? or *WAI to find
out when a sweep is finished before attempting to read data from the instru-
ment. Most commonly, you will send an INITiate command to take a single
sweep, then wait for the sweep to finish before executing the next command.
You also need to wait for any commands that perform a calibration or normal-
ization.
The recommended technique for waiting is to use the query form of *OPC
(*OPC?). This way, after initiating the sweep, you can do other things while
waiting for the instrument. When you do wait, make sure your GPIB time-out
is longer than what the instrument needs to finish the command. A typical
sequence would be:
sendMessage INIT;*OPC?
receiveInteger
Other alternatives involve polling the instrument for status, but that in turn
slows the instrument down by making it respond to the queries. If you must
poll for status, it is recommended that you send *ESE 1 to enable the OPC bit to
set bit 5 of the main status register, then use serial poll to query the main sta-
tus register.
Serial poll is a GPIB interface level operation, not a command like *STB?. It is
accessed using special commands. For VISA, use viReadStb. For NI 488.2, use
ibrsp. For SICL, use ireadstb(). For HP Basic for Windows, use SPOLL 723 or SPOLL
@WDCA.
Once the OPC bit is set, you will need to manually clear the status register. The
easiest way to do this is to send *CLS. You can also clear it by reading the regis-
ter with *ESR?
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Remote Operation
Summary for Experienced GPIB Programmers
// take a sweep
//perform other tasks while waiting
// wait for "1" indicating end of sweep
5-7
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