NI-VISA 15.0 Help Edition Date: June 2015 Part Number: 370131S-01 » This topic explains how to communicate with your USB device using NI-VISA. Recall that there are two classes of USB devices. The communication method depends on the device class. USB INSTR Class (USBTMC) Devices that conform to the USB Test and Measurement Class (USBTMC) use the NI-VISA USB INSTR class.

The following figure shows a LabVIEW VI that communicates with a USBTMC device. In this example, the VI opens a VISA session to a USB device, writes a command to the device, and reads back the response. In this example, the specific command being sent is the device ID query. Check with your device manufacturer for your device command set. 3 Learn LabVIEW. Your USB device is now installed and configured to use NI-VISA. To communicate with your device using VISA, use your device's VISA.

These devices use 488.2-style communication. For these devices, use the VISA Open, VISA Close, VISA Read, and VISA Write functions the same way as if communicating with GPIB instruments. The following figure shows a LabVIEW VI that communicates with a USBTMC device. In this example, the VI opens a VISA session to a USB device, writes a command to the device, and reads back the response. In this example, the specific command being sent is the device ID query.

Check with your device manufacturer for your device command set. After all communication is complete, the VI closes the VISA session. USBTMC LabVIEW Example Block Diagram USB RAW Class Communicating with the USB RAW class is more complicated, because each device may use its own communication protocol.

Contact your device vendor for details about the device communication protocol. Serial key blur pc game. USB communicates using four types of pipes or endpoints: control, bulk, interrupt, and isochronous. Each type of pipe transfers a different type of information. Also, any number of endpoints can be of any endpoint type.

Think of an endpoint as a communication socket. For specific details about USB architecture, review the. NI-VISA supports three types of USB pipes: control, bulk, and interrupt. When NI-VISA detects your USB instrument, it automatically scans your instrument for the lowest available endpoint for each type. When VISA detects the lowest available endpoint, it assigns that value to the appropriate VISA attribute.

The bulk in endpoint and bulk out endpoint are stored in the and attribute, respectively. The interrupt in endpoint is stored in the attribute. A value of –1 indicates a USB device does not support that type of pipe. For the control pipe, only endpoint zero is supported.

If you are using the C API, use the function to change endpoints. In LabVIEW, use a Write VISA Property Node. NI-VISA includes four functions to transfer data through USB pipes.

Before you can communicate with your device using these functions, you must set up the communication protocol using the VISA USB attributes. The following functions are available: • Use VISA USB Control In and VISA USB Control Out to transfer data using the control pipe. • To transfer data using a bulk pipe, use VISA Read and VISA Write.

• If you are using LabVIEW, VISA includes an additional function to use the interrupt pipe: VISA Get USB Interrupt Data. In the C API, you can do this by accessing the and attributes of the event object. To write an interrupt pipe out to a device, you first need to set the VI_USB_BULK_OUT_PIPE attribute in the C API or use the VISA USB Raw Out Pipe Property Node, shown below, in LabVIEW. Then, perform a VISA Write. VISA USB Raw Out Pipe Property Node.

History For years industry has moved towards purchasing instrumentation from a variety of vendors. This allows engineers to choose the best instruments for their application without being constrained to a specific vendor. This caused the invention of hardware standards like that were designed to allow interoperability between instruments of different vendors. Even with these standards in place, it was still a difficult task to build a test system with instruments from different vendors. In 1993 National Instruments, along with several companies including GenRad, Racal Instruments, and Tektronix, formed the VXIplug&play Systems Alliance.

VXI was the standard at the time for modular instrumentation. The goal of the alliance was to ensure multi-vendor interoperability for VXI systems and to reduce the development time for a fully working system including multi-vendor instrumentation. VISA was developed through this alliance with hopes of increasing productivity through a decrease in system setup time. Advantages of VISA One of VISA's advantages is that it uses many of the same operations to communicate with instruments regardless of the interface type. For example, the VISA command to write an ASCII string to a message-based instrument is the same whether the instrument is Serial, GPIB, or USB. Thus, VISA provides interface independence. This can make it easy to switch interfaces and also gives the users who must program instruments for different interfaces a single language they can learn.