Data Acquisition Toolbox

Line and Port Characteristics

As described in the preceding section, when you add lines to a digital I/O object, they must be configured for either input or output. You read values from an input line and write values to an output line. Whether a given hardware line is addressable for input or output depends on the port is resides on. You can classify digital I/O ports into these two groups based on your ability to address lines individually:

• Port-configurable devices - You cannot address the lines associated with a port-configurable device individually. This means that you must configure all the lines for either input or output. If you attempt to mix the two configurations, an error is returned.

You can add any number of available port-configurable lines to a digital I/O object. However, the engine will address all lines behind the scenes. For example, if one line is added to a DIO object, then you automatically get all lines. This means that if a digital I/O object contains lines from a port-configurable device, and you write a value to one or more of those lines, then all the lines are written to even if they are not contained by the device object.

• Line-configurable devices - You can address the lines associated with a line-configurable device individually. This means that you can configure individual lines for either input or output. Additionally, you can read and write values on a line-by-line basis. Note that for National Instruments E Series hardware, port 0 is always line-configurable, while all other ports are port-configurable.

You can return the line and port characteristics with the daqhwinfo function. For example, National Instruments AT-MIO-16DE-10 board has four ports and eight digital I/O lines per port. To return the digital I/O characteristics for this board

hwinfo = daqhwinfo(dio);

To display the line and port characteristics for the first port

hwinfo.Port(1)
ans = 
           ID: 0
      LineIDs: [0 1 2 3 4 5 6 7]
    Direction: 'in/out'
       Config: 'line'

To display the line and port characteristics for the second port

hwinfo.Port(2)
ans = 
           ID: 2
      LineIDs: [0 1 2 3 4 5 6 7]
    Direction: 'in/out'
       Config: 'port'

To display the line and port characteristics for the third port

hwinfo.Port(3)
ans = 
           ID: 3
      LineIDs: [0 1 2 3 4 5 6 7]
    Direction: 'in/out'
       Config: 'port'

To display the line and port characteristics for the fourth port

hwinfo.Port(4)
ans = 
           ID: 4
      LineIDs: [0 1 2 3 4 5 6 7]
    Direction: 'in/out'
       Config: 'port'

This information tells you that you can configure all 32 lines for either input or output, and that the first port is line-configurable while the remaining ports are port-configurable.

Adding Lines to a Digital I/O Object

Referencing Individual Hardware Lines