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What is USBTMC and How Can I Communicate with My USB Instrument?

Primary Software: Driver Software>>NI-VXI
Primary Software Version: 3.2
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem:
What is USBTMC and how can I communicate with my USB instrument using NI-VISA?

Solution:
USBTMC stands for USB Test & Measurement Class. USBTMC is a protocol built on top of USB that allows GPIB-like communication with USB devices. From the user's point of view, the USB device behaves just like a GPIB device. For example, you can use VISA Write to send the *IDN? query and use VISA Read to get the response. The USBTMC protocol supports service request, triggers and other GPIB specific operations.

USBTMC allows instrument manufacturers to upgrade the physical layer from GPIB to USB while maintaining software compatibility with existing software, such as instrument drivers and any application that uses VISA. This is also what the VXI-11 protocol provides for TCP/IP.

It is important to note that not all USB devices are USBTMC compliant. The device manufacturer has to add the support in the device firmware to support USBTMC. Traditional instruments (such as DMMs and scopes) with USB ports are most likely to support USBTMC. Refer to the instrument's documentation to determine if it is USBTMC compliant.

NI-VISA 3.0 or later allows you to communicate as a controller to USBTMC compliant devices. NI-VISA is configured to detect USBTMC compliant devices. To use such a device, plug it in and Windows should detect the new hardware and launch the New Hardware Wizard. Instruct the wizard to search for the driver, which in this case is NI-VISA. If NI-VISA is properly installed, the device will be installed as a USB Test & Measurement Class Device. Open Measurement & Automation Explorer (MAX). The new device will appear in MAX under Device and Interfaces » USB Devices. You can then use this resource name as you would use any GPIB resource.

On other operating systems such as Macintosh and Linux, plug an USBTMC device in. If NI-VISA 3.2 (or later) is installed properly, the device will be installed as a USB Test & Measurement Class Device. Open 'VisaConfig' application and the device will be listed under USB resources. You can use this resource name as you would use any GPIB resource.

For more information on the syntax of the resource name, refer to the description for viOpen in the NI-VISA Help, linked below.

Related Links:
Drivers and Updates: NI-VISA
Product Reference: NI-VISA Help
KnowledgeBase 325APJ2Y: How Can I Communicate With a Device Using NI-VISA USB Raw Mode?
NI Developer Zone Tutorial: USB Instrument Control Tutorial
Universal Serial Bus (USB) Website

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Report Date: 10/02/2003
Last Updated: 12/27/2007
Document ID: 321A2A2Y

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