VISA Read Function

LabVIEW 2018 Help

Edition Date: March 2018
Part Number: 371361R-01
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Owning Palette: VISA VIs and Functions

Requires: Base Development System

Reads the specified number of bytes from the device or interface specified by VISA resource name and returns the data in read buffer.

Details  Examples

VISA resource name specifies the resource to be opened. The VISA resource name control also specifies the session and class.
byte count is the number of bytes to be read.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
VISA resource name out is a copy of the VISA resource name that VISA functions return.
read buffer contains the data read from the device.
return count contains the number of bytes actually read.
error out contains error information. This output provides standard error out functionality.

VISA Read Details

This function might return less than the number of bytes requested if the function reaches the end of the buffer, reaches a termination character, or if a timeout occurs. The output error cluster indicates if a timeout has occurred.

Whether the data is read synchronously or asynchronously is platform-dependent. Right-click the node and select Synchronous I/O Mode»Synchronous from the shortcut menu to read data synchronously.

When you transfer data from or to a hardware driver synchronously, the calling thread is locked for the duration of the data transfer. Depending on the speed of the transfer, this can hinder other processes that require the calling thread. However, if an application requires that the data transfer as quickly as possible, performing the operation synchronously dedicates the calling thread exclusively to this operation.

Note  In most applications, synchronous calls are slightly faster when you are communicating with 4 or fewer instruments. Asynchronous operations result in a significantly faster application when you are communicating with 5 or more instruments. The LabVIEW default is asynchronous I/O.


Refer to the following VIs for examples of using the VISA Read function:

  • Continuous Serial Write and Read VI: labview\examples\Instrument IO\Serial
  • USB RAW - Bulk VI: labview\examples\Instrument IO\VISA\USB
  • GPIB with VISA functions VI: labview\examples\Instrument IO\GPIB


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