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The DISP OFF command is unusual in that a *RST or a SYST:PRES does not turn
the display back on. Once off, the display stays off until you want it to come
back on.
Combine commands into a single message
The instrument will execute commands faster if it receives them all in a single
message. For example:
sendMessage INIT
sendMessage *OPC?
receiveInteger
This is inefficient because the instrument will receive and parse the INIT com-
mand, and actually launch the sweep before returning to GPIB to receive and
parse the *OPC?. The instrument will hold off GPIB for several hundred milli-
seconds before accepting the *OPC? message. Instead, combine them into a
single message:
sendMessage INIT:*OPC?
receiverInteger
A good rule of thumb is to combine closely related commands. For example,
sending the OPC with the command it waits for makes good sense. If you are
only changing one or two sweep parameters, you might include that in the
message also. Avoid putting too much in a single message, as this makes it dif-
ficult to read and rearrange your application program contents.
Transfer traces when more than 2 marker operations
Modern controllers have plenty of processing power to calculate trace statis-
tics, and can often calculate faster than the instrument. The rule of thumb is
that if you perform more than two marker functions (and associated value
read back), it is more efficient to transfer the trace and do the post-processing
in your computer. It takes about 1/4 second to transfer a 1000 point trace
using a 32 bit binary transfer.
Use 32 bit binary trace transfers
The most convenient trace transfer is an ASCII trace transfer, but download-
ing the data in REAL32 format is substantially faster. Binary can take half as
long as ASCII, which saves about 100 ms for every 1000 points transferred.
ASCII format sends the trace value reformatted as 12 character strings,
whereas a 32 bit binary transfer sends the data in IEEE 32 bit format. This is
the same representation used inside the instrument and takes only 4 8-bit
data bytes. There are two binary transfer formats available - IEEE 32 bit and
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WDCA Techniques to Improve Throughput
// take a sweep
// instrument tells us when done
// wait for reply
// take a sweep, instrument tells us when done
// wait for reply
Remote Operation
5-29
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