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Working with the USB Interface

Creating a VISA-USB Object

You create a VISA-USB object with the visa function. Each VISA-USB object is associated with an instrument connected to a USB port on your computer.

visa requires the vendor name and the resource name as input arguments. The vendor name can be agilent, ni, or tek. The resource name consists of the USB board index, manufacturer ID, model code, serial number, and interface number of the connected instrument. You can find the VISA-USB resource name for a given instrument with the configuration tool provided by your vendor, or with the instrhwinfo function. (In place of the resource name, you can use an alias as defined with your VISA vendor configuration tool.) As described in Connecting to the Instrument, you can also configure property values during object creation.

Before you create a VISA object, you must find the instrument in the appropriate vendor VISA explorer. When you find the instrument configured, note the resource string and create the object using that information. For example, to create a VISA-USB object that uses National Instruments® VISA,

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

The VISA-USB object vu now exists in the MATLAB® workspace.

To open a connection to the instrument, type:

fopen (vu);

You can display the class of vu with the whos command.

whos vu
  Name      Size         Bytes  Class

  vu        1x1            882  visa object

Grand total is 15 elements using 882 bytes

After you create the VISA-USB object, the properties listed below are automatically assigned values. These properties provide descriptive information about the object based on its class type and address information.

VISA-USB Descriptive Properties

Property Name

Description

Name

Specify a descriptive name for the VISA-USB object.

RsrcName

Indicate the resource name for a VISA instrument.

Type

Indicate the object type.

You can display the values of these properties for vs with the get function.

get(vu,{'Name','RsrcName','Type'})
ans = 
'VISA-USB-0-0x1234-125-A22-5-0' 'USB::0x1234::125::A22-5::INSTR'  
'visa-usb'

VISA-USB Object Display

The VISA-USB object provides you with a convenient display that summarizes important address and state information. You can invoke the display summary these three ways:

  • Type the VISA-USB object at the command line.

  • Exclude the semicolon when creating a VISA-USB object.

  • Exclude the semicolon when configuring properties using the dot notation.

You can also display summary information via the Workspace browser by right-clicking an instrument object and selecting Display Summary from the context menu.

The display summary for the VISA-USB object vs is given below.

VISA-USB Object Using NI Adaptor : VISA-USB-0-0x1234-125-A22-5-0  

Communication Address
   ManufacturerID:     0x1234
   ModelCode:          125
   SerialNumber:       A22-5  

Communication State
   Status:             closed
   RecordStatus:       off  

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

VISA-USB Address

The VISA-USB address consists of

  • Board index (optional, from the VISA configuration)

  • Manufacturer ID of the instrument

  • Model code of the instrument

  • Serial number of the instrument

  • Interface number (optional, from the VISA configuration)

You specify these address property values via the resource name during VISA-USB object creation. The instrument address properties are given below.

VISA-USB Address Properties

Property Name

Description

BoardIndex

Specify the index number of the USB board in VISA configuration (optional — defaults to 0).

InterfaceIndex

Specify the USB interface number (optional).

ManufacturerID

Specify the manufacturer ID of the USB instrument.

ModelCode

Specify the model code of the USB instrument.

SerialNumber

Specify the index of the USB instrument on the USB hub.

The properties are automatically updated with the specified resource name values when you create the VISA-USB object.

With the get function, you can display the address property values for the VISA-USB object vu, created in Creating a VISA-USB Object.

fopen(vu)
get(vu,{'ManufacturerID','ModelCode','SerialNumber'})
ans = 
    [0x1234]    [125]    [A22-5]
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