Every switch channel has a usage type associated with it. By default, most channels are considered load channels. In terms of usage, a load channel is essentially a channel with no special capabilities. The NI-DAQmx switch API offers two additional usage types for a given channel for added software protection against unintentional damage to your system. These additional types are source and reserved for routing. Setting a channel as source indicates to NI-DAQmx that a signal source is connected to this channel. NI-DAQmx does not allow two user-defined source channels to be directly or indirectly connected. Setting a channel as reserved for routing indicates to NI-DAQmx that you are not planning on wiring directly to the channel and that it is available for NI-DAQmx for routing as needed.
Configuring the usage of a channel provides additional software protection when using the Connect/Disconnect or scanning functions/VIs, but it does not provide additional protection when manipulating relays directly using the Open/Close Relay functions/VIs. National Instruments recommends against mixing the two types of function/VI calls.
You can change the default usage type for channels while configuring devices in MAX. By changing the default values for channel usage on each topology, you are setting the defaults that will be used for those attributes/properties when a reset is called.