5. Instruments Drivers vs. Direct SCPI Commands

In the previous chapters, we learned how to remote control Rohde & Schwarz instruments using direct SCPI commands. As an alternative, Rohde & Schwarz offers free instrument drivers that provide an abstraction layer between your application and the instrument’s SCPI commands.

Instead of using VISA Write / Read functions and direct SCPI commands, you use functions and attributes of an instrument driver. A simple example of such substitution in the LabVIEW rsscope Instrument driver:

The same substitution in C# using the IVI.NET RsScope instrument driver. You set the individual parameters with properties, or set more of them with a method:

For simplicity, the above direct SCPI command pictures do not contain all the operations that the instrument drivers perform. For example, the drivers also wait for the instrument acknowledgment that a command has been executed (see Chapter 6 Measurement Synchronization), and check for potential errors after each command (see Chapter 7 Instrument Error Checking). When you use direct SCPI commands, you have to take care of both of these tasks yourself.

Summarized advantages/disadvantages of using direct SCPI commands

Advantages:

• Quicker start; Instrument user manual has all the SCPI commands described.
• Faster execution speed.

Disadvantages:

• You need to take care of the measurement synchronization and the instrument error checking.
• You must format arguments into SCPI commands. This is especially tricky with binary data.
• When you receive an instrument string response, you need to convert it into an appropriate type (e.g. integer, double or boolean, arrays or binary data).

Summarized advantages/disadvantages of using the instrument drivers

Advantages:

• Performing error checking after each command. You can switch this off for the critical sections where you require the maximum speed.
• Synchronization of commands that take long time to complete.
• Formatting of arguments into the SCPI commands and parsing the instrument responses is already implemented.
• Instrument drivers come with their own *.chm help files.
• They always offer the option of using direct SCPI commands.

Disadvantages:

• Longer learning curve, you have to get familiar with the driver structure.
• Minor overhead. This can be minimized by the correct approach; see Chapter 8 Speed Optimization
• Sometimes you have to wait until new instrument features are supported by instrument drivers.

Suitability of Rohde & Schwarz Instrument drivers for different programming languages

The following table shows, which instrument driver is suitable for which programming language. The specifics of the different environments we discuss afterwards.

For Python users

Rohde & Schwarz currently provides Python 3.6+ SCPI-based instrument drivers for these instruments on the pypi repository: CMW,SMx, CMA, CMX/CMP, OSP.
For instruments which do not provide Python instrument drivers, we recommend using direct SCPI commands.

For MATLAB users

Rohde & Schwarz provides MATLAB MDD drivers. Using MDD drivers requires advanced knowledge of VXI plug&play driver structure, you must manually import all enumeration constants from the driver header file. In addition, you need a MATLAB Instrument Control Toolbox license. For MATLAB users we recommend using direct SCPI commands. This application note covers both approaches:

1MA171: How to use Rohde & Schwarz Instruments in MATLAB

For LabVIEW users

Rohde & Schwarz provides native LabVIEW drivers. Find out more in the application note:

1MA228: 10 Tips & Tricks on how to use Rohde & Schwarz LabVIEW Instrument drivers

For C#, VB.NET users

Here, you have two choices:

• IVI.NET drivers - available for almost all the instruments. Here you can also use the VXI plug&play drivers that come with the C# and VB.NET wrapper classes.Find out more in the dedicated application note:
  1MA268: How to use Rohde & Schwarz IVI.NET Instrument drivers
  Download them from our product websites.
• SCPI-based drivers - these drivers are auto-generated fro the instrument's SCPI tree and follow exactly the SCPI tree syntax. Use them if you are used to SCPI commands. These drivers offer intellisense help and type-safe interface for the SCPIs. Download them as NuGet packages from the nuget.org:
  https://www.nuget.org/profiles/rohde-schwarz

For LabWindows/CVI and other C/C++ environment users

VXI plug&play drivers are compiled CVI drivers for 32-bit and 64-bit Windows applications. You can use them both in C/C++ languages.

To use a CVI driver, add its entire source code into your project.

To use a VXI plug&play driver, add the driver's LLB file (for static linking) or its DLLs file (for dynamic linking) into your project.