Documentation

Configuring and Connecting to the Instrument

You need to create a VISA-GPIB object. In this example, an object is created using the ni driver and the VISA resource string shown below.

v = visa('ni', 'GPIB0::2::INSTR');

Before you can perform a read or write operation, you must connect the VISA-GPIB object to the instrument with the fopen function.

fopen(v);

If the object was successfully connected, its Status property is automatically configured to open.

v.Status
ans = 
    open

Writing ASCII Data

You use the fprintf function to write ASCII data to the instrument. For example, the'Display:Contrast' command will change the display contrast of the oscilloscope.

fprintf(v, 'Display:Contrast 45');

By default, the fprintf function operates in a synchronous mode. This means that fprintf blocks the MATLAB^® command line until one of the following occurs:

By default the fprintf function writes ASCII data using the %s\n format. You can also specify the format of the command written by providing a third input argument to fprintf. The accepted format conversion characters include: d, i, o, u, x, X, f, e, E, g, G, c, and s. For example:

fprintf(v, '%s', 'Display:Contrast 45');

ASCII Write Properties

OutputBufferSize

The OutputBufferSize property specifies the maximum number of bytes that can be written to the instrument at once. By default, OutputBufferSize is 512.

v.OutputBufferSize
ans = 
    512

If the command specified in fprintf contains more than 512 bytes, an error is returned and no data is written to the instrument.

EOIMode, EOSMode, and EOSCharCode

By default, the End or Identify (EOI) line is asserted when the last byte is written to the instrument. This behavior is controlled by the EOIMode property. When EOIMode is set to on, the EOI line is asserted when the last byte is written to the instrument. When EOIMode is set to off, the EOI line is not asserted when the last byte is written to the instrument.

All occurrences of \n in the command written to the instrument are replaced with the EOSCharCode property value if EOSMode is set to write or read&write.

ValuesSent

The ValuesSent property is updated by the number of values written to the instrument. Note that by default EOSMode is set to none. Therefore, EOSCharCode is not sent as the last byte of the write.

fprintf(v, 'Display:Contrast 45');
v.ValuesSent
ans = 
    57

Clear any data in the input buffer before moving to the next step.

flushinput(v);

Reading ASCII Data

You use the fscanf function to read ASCII data from the instrument. For example, the oscilloscope command 'Display:Contrast?' returns the oscilloscope's display contrast:

fprintf(v, 'Display:Contrast?');
data = fscanf(v)

data =

    45

fscanf blocks until one of the following occurs:

By default, the fscanf function reads data using the '%c' format. You can also specify the format of the data read by providing a second input argument to fscanf. The accepted format conversion characters include: d, i, o, u, x, X, f, e, E, g, G, c, and s. For example, the following command will return the voltage as a decimal:

fprintf(v, 'Display:Contrast?');
data = fscanf(v, '%d')

data =

    45

isnumeric(data)

ans =

    1

ASCII Read Properties

InputBufferSize

The InputBufferSize property specifies the maximum number of bytes you can read from the instrument. By default, InputBufferSize is 512.

v.InputBufferSize
ans = 
    512

ValuesReceived

The ValuesReceived property indicates the total number of values read from the instrument. Note the last value received is a linefeed.

fprintf(v, 'Display:Contrast?');
data = fscanf(v)

data =

    45

v.ValuesReceived

ans =

     9

EOSMode and EOSCharCode

To terminate the data transfer based on receiving EOSCharCode, you should set the EOSMode property to read or read&write and the EOSCharCode property to the ASCII code for which the read operation should terminate. For example, if you set EOSMode to read and EOSCharCode to 10, then one of the ways that the read terminates is when the linefeed character is received.

The standard response to the vertical gain query is in scientific notation.

fprintf(v, 'CH1:Scale?')
data = fscanf(v)

data =

    1.0E0

Now configure the VISA-GPIB object to terminate the read operation when the 'E' character is received. The first read terminates when the 'E' character is received.

set(v, 'EOSMode', 'read')
set(v, 'EOSCharCode', double('E'))
fprintf(v, 'CH1:Scale?')
data = fscanf(v)

data =

1.0E

If you perform a second read operation, it terminates when the EOI line is asserted.

data = fscanf(v)

data =

    0

Cleanup

If you are finished with the VISA-GPIB object, disconnect it from the instrument, remove it from memory, and remove it from the workspace.

fclose(v);
delete(v);
clear v