National Instruments NI-VXI - Manual (Page 27)

Chapter 2 Introduction to the NI-VXI Functions
NI-VXI User Manual 2-8 © National Instruments Corporation
Most functions that take a controller parameter will allow you to pass
(-1) as the logical address. This selects the default controller for the
system. Notice that the default controller is determined by the
following factors:
• If the program is running on an embedded controller, the default
controller is the embedded controller.
• If the program is running on an external controller, you will be
able to configure whether the default controller is the external
controller or the remote controller with the lowest numbered
logical address. With this behavior, if you write a program on an
embedded controller referring to the controller as logical
address-1, you will be able to swap the embedded controller
configuration with an external controller configuration without
changing your source code.
Notice that -1 is never a valid value for the extender parameter. In
addition, the logical addresses of embedded and external controllers
also are never valid values for the extender parameter. The extender
parameter refers only to devices that can map interrupt lines, trigger
lines, or other signals into or out of a frame.