this is an error report regarding the BF548 CAN module documentation
in the latest HRM (V1.0, Aug. 2010).
It says that the bits in the global interrupt flag register are of type W1C,
i.e. writing a '1' clears the bit. This is NOT true.
The interrupt status and flag bits can only be cleared by writing
to the global interrupt status register, not the interrupt flag register.
Obviously the global interrupt flag register value is just a combinational
AND of the interrupt status and the interrupt mask register values.