Data Acquisition Toolbox

Reading Digital Values

You can read values from one or more lines with the getvalue function. getvalue requires the DIO object as an input argument. You can optionally specify an output argument, which represents the returned values as a binary vector. Binary vectors are described in Writing Digital Values.

For example, suppose you create the digital I/O object dio and add eight input lines to it from port 0.

• dio = digitalio('nidaq',1);
  addline(dio,0:7,'in');
  

To read the current value of all the lines contained by dio:

• portval = getvalue(dio)
  portval =
       1     1     1     0     1     0     0     0
  

To read the current values of the first five lines contained by dio:

• lineval = getvalue(dio.Line(1:5))
  lineval =
       1     1     1     0     1
  

You can convert a binvec to a decimal value with the binvec2dec function. For example, to convert the binary vector lineval to a decimal value:

• out = binvec2dec(lineval)
  out =
      23
  

Rules for Reading Digital Values

Reading values from digital I/O lines follows these rules:

• If the DIO object contains lines from a port-configurable device, then all lines are read even if they are not contained by the device object. However, only values from the lines contained by the object are returned.
• You can always read from a line configured for output.
• For National Instruments hardware, lines configured for input return a value of 1 by default.
• getvalue always returns a binary vector (binvec). To convert the binvec to a decimal value, use the binvec2dec function.

Writing and Reading Digital I/O Line Values

Example: Writing and Reading Digital Values