Hi Linjack
Unlike National Instruments' data acquisition cards or CAN cards from other vendors, the NI CAN cards are not programmed through registers. Instead of just mapping the registers of the CAN controller into the host memory, there is a CPU on the CAN card that communicates with the CAN controller. Thus, the communication with the CAN card is actually a communication between two processors through a shared memory window, which is much more complicated than simple register access.
Part of that shared memory communication architecture is patented (see US patend # 6122713).
-B2k