Interchangeability warnings indicate that using your application with a different instrument might cause different behavior. You can use the ClassPrefix_GetNextInterchangeWarning function to retrieve interchangeability warnings. Alternately, you can use NI I/O Trace to view interchangeability warnings.
Interchangeability checking is performed on a capability group basis. When enabled, interchangeability checking is always performed on the base capability group. Interchangeability is performed on extension capability groups when the user has set a value for any attribute in the group. If you do not set the value of any attribute of an extension capability group, interchangeability checking is not performed on that group.
In general, interchangeability warnings are generated if the following conditions are encountered:
- An attribute that affects the behavior of the instrument is not in a state that you specify. This can happen if your program does not configure the attribute or if your program configures the attribute but the value becomes invalid as a result of your program configuring a different attribute.
- You set, get, or check an instrument specific attribute.
- You set an attribute for which the IVI class specification defines values to an instrument specific value.
- You pass an instrument specific value to a function parameter for which the IVI class specification defines values.
- You attempt to set an attribute that the class defines as read-only. In some cases the class drivers define read-only attributes that specific drivers might implement as read/write.
- The class driver encounters an error when it tries to disable an extension capability group that your program does not use. The purpose of disabling unused extension groups is to make your program behave the same regardless of whether the instruments you use implement the extension capability group. Some instruments that implement the extension capability group might not support the value to which the class driver attempts to set the attribute. In this case, the class driver queues an interchangeability warning instead of returning an error from the function.
Refer to the following topics for more information about interchangeability checking for a particular IVI class driver:
IviDCPwr—AC Power Supply
IviDCPwr—DC Power Supply
IviRFSigGen—RF Signal Generator