Instrument Control Toolbox 2.9

Introduction to VISA

Contents

Introduction

Virtual Instrument Standard Architecture (VISA) is a standard defined for communicating with instruments. The standard provides a common language for communicating with instruments, regardless of the interface.

The Instrument Control Toolbox™ VISA object supports seven communication interface types: serial, GPIB, GPIB-VXI, VXI, TCPIP, USB, and RSIB. Note, only National Instrument's VISA with the Rohde & Schwarz VISA passport supports the RSIB interface type.

Supported Vendors

You create a VISA object using the VISA function. v = visa('Vendor', 'ResourceName');

The following list defines the supported vendors:

  Vendor                 Description
  ======                 ===========
  agilent                Agilent Technologies® VISA.
  ni                     National Instruments® VISA.
  tek                    Tektronix® VISA.

Supported Interfaces

The following list defines how the different interfaces are defined at object creation:

  Interface           ResourceName
  =======             ============
  serial              ASRL[port]::INSTR
  gpib                GPIB[board]::primary_address::[secondary_address]::INS
TR
  gpib-vxi            GPIB-VXI[chassis]::vxi_logical_address::INSTR
  vxi                 VXI[chassis]::vxi_logical_address::INSTR
  tcpip               TCPIP[board]::remote_host::[lan_device_name]::INSTR
  usb                 USB[board]::manid::model_code::serial_No::[interface_N
o]::INSTR
  rsib                RSIB::remote_host::INSTR

The following describes the parameters used in the list above:

  port                The serial port.
  board               Board index of the gpib board.
  chassis             Index of the VXI system.
  interface_No        USB interface.
  lan_device_name     Local Area Network (LAN) device name.
  manid               Manufacturer ID of the USB instrument.
  model_code          Model code for the USB instrument.
  primary_address     Primary address of the gpib board.
  remote_host         Host name or IP address of the instrument.
  secondary_address   Secondary address of the gpib board.
  serial_No           Index of the instrument on the USB hub.
  vxi_logical_address Logical address of the vxi board.

The parameters in brackets [] are optional. All parameters that are optional default to 0, except port, which defaults to 1, and lan_device_name, which defaults to inst0.

The Serial Interface

Serial communication is the simplest and most common low-level protocol for communicating between two or more devices. Normally, one device is a computer, while the other device can be a modem, a printer, a data acquisition device, or another computer.

As the name suggests, the serial port sends and receives bytes of information in a serial fashion, one bit at a time. These bytes can be transmitted using either a binary format or an ASCII format.

Communication is accomplished using three transmission lines: the Transmit Data line, the Receive Data line, and the Ground. Other lines are available for handshaking, but are not required.

Creating a VISA-Serial Object

The following command creates a VISA-serial object.

vserial = visa('ni', 'ASRL1::INSTR')

   VISA-Serial Object Using NI Adaptor : VISA-Serial-ASRL1

   Communication Settings
      Port:               ASRL1
      BaudRate:           9600
      Terminator:         'LF'

   Communication State
      Status:             closed
      RecordStatus:       off

   Read/Write State
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0

The VISA-serial object, vserial, communicates with an instrument connected to the ASRL1 (which is defined as the COM1) port. The National Instruments VISA DLL is installed on the computer and used to communicate with the instrument.

The GPIB Interface

General Purpose Interface Bus (GPIB), also known as the IEEE® 488 interface, is a standard interface for communicating between two or more devices. The bus supports one controller (usually a computer) and up to fourteen additional instruments.

Eight bits of data are transferred in parallel along the bus using a three wire handshake: the Data Valid line, the Not Data Accepted line, and the Not Ready for Data line. The three wire handshake assures reliable data transfer at the rate determined by the slowest device. Data transfer rates can exceed 1 Mbyte/second.

Creating a VISA-GPIB Object

The following command creates a VISA-GPIB object.

vgpib = visa('ni', 'GPIB0::2::0::INSTR')

   VISA-GPIB Object Using NI Adaptor : VISA-GPIB0-2

   Communication Address
      BoardIndex:         0
      PrimaryAddress:     2
      SecondaryAddress:   0

   Communication State
      Status:             closed
      RecordStatus:       off

   Read/Write State
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0

The VISA-GPIB object, vgpib, communicates with an instrument through a GPIB board with board index 2. The instrument has a primary address of 4 and no secondary address. The National Instruments VISA DLL is installed on the computer and is used to communicate with the instrument.

The VXI Interface

A VXI system consists of a chassis, VXI instruments, a slot 0 card, and a resource manager. The slot 0 card controls the VXI backplane. The resource manager configures the modules for proper operation whenever the system is powered on or reset (the slot 0 card can also be the resource manager). The chassis holds the VXI instruments, the slot 0 card, and the resource manager, and contains the VXI backplane.

VXI instruments can be either message-based or register- based. A message-based instrument is generally easier to use than a register-based instrument. While a register- based instrument is generally faster than a message-based instrument.

The VXI interface uses an embedded VXI controller (in slot 0) to access the VXI instruments over the VXI backplane.

Creating a VISA-VXI Object

The following command creates a VISA-VXI object.

vvxi = visa('agilent', 'VXI0::8::INSTR')

The VISA object, vvxi, communicates with a VXI instrument located at logical address 8 in the first VXI chassis.

The GPIB-VXI Interface

The GPIB-VXI interface is similar to the VXI interface, however, there is a GPIB controller in slot 0. The GPIB controller contains a GPIB connector that is connected to a GPIB board in your computer. The GPIB controller can communicate to instruments in the chassis over the VXI backplane.

Creating a VISA-GPIB-VXI Object

The following command creates a VISA-GPIB-VXI object.

vgpibvxi = visa('ni', 'GPIB-VXI0::16::INSTR')

   VISA-GPIB-VXI Object Using NI Adaptor : VISA-GPIB-VXI0-16

   Communication Address
      ChassisIndex:       0
      LogicalAddress:     16

   Communication State
      Status:             closed
      RecordStatus:       off

   Read/Write State
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0

The VISA object, vgpibvxi, communicates with a VXI instrument located at logical address 16 in the first VXI system.

The TCPIP Interface

The TCPIP interface allows you to communicate with an instrument using the VXI-11 interface. It allows you to communicate with a networked instrument.

Creating a VISA-TCPIP Object

The following command creates a VISA-TCPIP object.

vtcpip = visa('ni', 'TCPIP::216.148.60.170::INSTR')

   VISA-TCPIP Object Using NI Adaptor : VISA-TCPIP-0-216.148.60.170-inst0

   Communication Address
      RemoteHost:         216.148.60.170

   Communication State
      Status:             closed
      RecordStatus:       off

   Read/Write State
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0

The VISA object, vtcpip, communicates with an instrument configured with IP address 216.148.60.170.

The USB Interface

The USB interface allows you to communicate with an instrument that has a USB interface.

Creating a VISA-USB Object

The following command creates a VISA-USB object.

vusb = visa('ni', 'USB::0x1234::125::A22-5::INSTR')

   VISA-USB Object Using NI Adaptor : VISA-USB-0-0x1234-0x007D-A22-5-0

   Communication Address
      ManufacturerID:     0x1234
      ModelCode:          0x007D
      SerialNumber:       A22-5

   Communication State
      Status:             closed
      RecordStatus:       off

   Read/Write State
      TransferStatus:     idle
      BytesAvailable:     0
      ValuesReceived:     0
      ValuesSent:         0

The VISA object, vusb, communicates with a USB instrument with manufacturer ID 0x1234, model code 125 and serial number A22-5. The instrument is using the first available USBTMC interface.

The RSIB Interface

The RSIB interface is supported by National Instruments VISA only. It also requires the Rohde & Schwarz VISA passport. The RSIB interface allows you to communicate with Rohde & Schwarz spectrum analyzers, network analyzers, and test receivers.

Creating a VISA-RSIB Object

The following command creates a VISA-RSIB object.

vrsib = visa('ni', 'RSIB::192.168.1.33::INSTR')

The VISA object, vrsib, communicates with an Rohde & Schwarz spectrum analyzer configured with IP address 192.168.1.33.

Obtaining Hardware Information for Your Computer

You can use the INSTRHWINFO function to obtain information about the hardware installed in your computer. For example, the following command lists the available serial ports, GPIB boards, and VXI chassis.

info = instrhwinfo('visa', 'ni')

info =

             AdaptorDllName: 'V:\matlab\toolbox\instrument\instrumentadaptor
s\win32\mwnivisa.dll'
          AdaptorDllVersion: 'Version 2.3'
                AdaptorName: 'NI'
           AvailableChassis: []
       AvailableSerialPorts: {2x1 cell}
          InstalledBoardIds: [2x1 double]
      ObjectConstructorName: {5x1 cell}
                SerialPorts: {2x1 cell}
              VendorDllName: 'visa32.dll'
    VendorDriverDescription: 'National Instruments VISA Driver'
        VendorDriverVersion: 3.3000

info.ObjectConstructorName

ans =

    'visa('ni', 'ASRL1::INSTR');'
    'visa('ni', 'ASRL10::INSTR');'
    'visa('ni', 'GPIB0::2::INSTR');'
    'visa('ni', 'GPIB0::4::INSTR');'
    'visa('ni', 'GPIB2::30::INSTR');'