The I/O (receive and transmit) buffers can be manually set in LabVIEW or LabWindows/CVI.LabVIEW:
Use the VISA Set I/O Buffer Size function to set the size (in bytes) of the receive or transmit buffer.
The mask input designates whether to set the I/O receive buffer, I/O transmit buffer, or both. Size is the size of the buffer in bytes. You should set the buffer size to a value larger than the number of bytes you expect to read or write. If size is left unwired, a size of 4096 bytes is used. LabWindows/CVI:
In LabWindows\CVI use the VISA viSetBuf function.
ViStatus viSetBuf(ViSession vi, ViUInt16 mask, ViUInt32 size
For more information on how to set the mask parameter, refer to the NI-VISA help file
for this function.