Abstract: An integrated circuit comprises a scan chain with parallel inputs and outputs coupled to a functional circuit. A scan chain modifying circuit is provided coupled to the scan chain. When testing is authorized the scan chain modifying circuit operates in a mode wherein a normal shift path is provided through the scan chain. When testing is not authorized the scan chain modifying circuit operates to effect spontaneous dynamic changes in the shift path, which dynamically vary the length of the shift path between external terminals of the integrated circuit while shifting takes place. In an embodiment the dynamical variations are controlled by a running key comparison. In other embodiments running key comparison is used to disable transfer through the scan chain or operation of functional circuits.

Abstract: A memory region protection unit is disclosed that comprises a first register for storing a memory region address, a second register for storing the memory region size, an arithmetic function block for executing an arithmetic function on a memory address provided to the region protection unit and the address value in the first register. The unit further has a comparator for comparing the output of the arithmetic function block with the size value in the second register, the comparator being coupled to an output for signalling the validity of the memory address on the bus The region protection unit has a controller configured to retrieve the memory region address and the memory region size from instructions issued to the region protection unit for associating the unit with said region, and to dissociate the unit from its memory region in response to a further instruction.

Abstract: A memory region protection unit is disclosed that comprises a first register for storing a memory region address, a second register for storing the memory region size, an arithmetic function block for executing an arithmetic function on a memory address provided to the region protection unit and the address value in the first register. The unit further has a comparator for comparing the output of the arithmetic function block with the size value in the second register, the comparator being coupled to an output for signalling the validity of the memory address on the bus The region protection unit has a controller configured to retrieve the memory region address and the memory region size from instructions issued to the region protection unit for associating the unit with said region, and to dissociate the unit from its memory region in response to a further instruction.