Instrument Control (GPIB, Serial, VISA, IVI)

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What exactly is Bytes at Port referring to ?

I'm looking at a previously developed application which uses VISA Read to read 'Bytes at Port' bytes. As I need to make some changes I'd first like to understand how it manages to sucessfully read messages over 128 bytes despite the fact that our PCI-8433/2 card has a FIFO buffer of only 128 bytes.

 

I'm sure nothing clever is going on. The buffer is flushed before and after a single read (all within a loop), and the received data is sent to the Front Panel.

 

I'm assuming VISA is buffering the data itself to a virtual port that it creates itself, but this isn't mentioned in the documentation.

 

Any answers ?

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It is the number of bytes in the main memory buffer of the pc. Created by the OS and not VISA.

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