Data Acquisition Toolbox

Reading Digital Values

You can read values from one or more digital I/O lines with the getvalue function. getvalue requires the digital I/O 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 and return the result to out

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

To read the current values of the first four lines contained by dio and return the result to out

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 digital I/O 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 digital I/O 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