LabVIEW does not release GPIB bus.

[JÞB]

Lets clear up a few thing here.

IEEE-488 used to be known a HPIB.  it involves some hardware (Phy Layer) and some data layer requirements *and many optional implementations of data layer packages (Those * packages have few requirements other than to "Ignore if not implemented")  There are devices that "F" it up!  I once used a device that "Quit Controlling" - a QU command- whenever it received an *IFC!  

488.2 IS SCPI, That me say that again for the poster that mistakenly contradicted that 488.2 IS SCPI!  But, not every instrument type had every command type defined at the same time.  SCPI commands are defined by instrument class as per the IVI Consortium.   A VNA falls into a category of instruments where IVI had not fully defined the class before the "B" model was produced. The upgraded (firmware) in the "B" model may have more than one "Sys:Lang" parameter.  The C model would implement the hardware required for the *WAI that was (and still is) an Optional 488.2 requirement.

[cstorey]

Sorry Jeff, its a bit semantic but SCPI is not IEEE 488.2.  One defines the communication protocol and the other the command structure.  SCPI can be used on non-488.2 hardware (RS232/488/USB).  See..

https://en.wikipedia.org/wiki/IEEE-488

https://en.wikipedia.org/wiki/Standard_Commands_for_Programmable_Instruments

While IEEE 488.1 defined the hardware and IEEE 488.2 defined the protocol, there was still no standard for instrument-specific commands. Commands to control the same class of instrument, e.g., multimeters, would vary between manufacturers and even models.

The United States Air Force,^[4] and later Hewlett-Packard, recognized this problem. In 1989, HP developed their TML language^[5] which was the forerunner to Standard Commands for Programmable Instrumentation (SCPI). SCPI was introduced as an industry standard in 1990.^[6] SCPI added standard generic commands, and a series of instrument classes with corresponding class-specific commands. SCPI mandated the IEEE 488.2 syntax, but allowed other (non-IEEE 488.1) physical transports.

The Hp8510C did not support IEEE 488.2 or SCPI, but did support 488.1 GPIB and defined its own set of commands.   

[JÞB]

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@cstorey wrote:

Sorry Jeff, its a bit semantic but SCPI is not IEEE 488.2.  One defines the communication protocol and the other the command structure.  SCPI can be used on non-488.2 hardware (RS232/488/USB).  See..

https://en.wikipedia.org/wiki/IEEE-488

https://en.wikipedia.org/wiki/Standard_Commands_for_Programmable_Instruments

While IEEE 488.1 defined the hardware and IEEE 488.2 defined the protocol, there was still no standard for instrument-specific commands. Commands to control the same class of instrument, e.g., multimeters, would vary between manufacturers and even models.

The United States Air Force,^[4] and later Hewlett-Packard, recognized this problem. In 1989, HP developed their TML language^[5] which was the forerunner to Standard Commands for Programmable Instrumentation (SCPI). SCPI was introduced as an industry standard in 1990.^[6] SCPI added standard generic commands, and a series of instrument classes with corresponding class-specific commands. SCPI mandated the IEEE 488.2 syntax, but allowed other (non-IEEE 488.1) physical transports.

The Hp8510C did not support IEEE 488.2 or SCPI, but did support 488.1 GPIB and defined its own set of commands.   

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Don't go there. several instrument mfgs have claimed compliance to IEEE488.1 There is no such thing! 488, 488.2 Other than that mfgs have tried to bamboozle you!   488.1 is like RS-232. Dou you know what the "RS" is short for?  (Recommended Standard)

point to a definition of IEEE488-1 (its SCPI wannabe)  Then RTM for the 6603B and understand the SYStem:LANGuage command  <SCPI|HPPSL>