1. A control device coupled between a first memory and a second memory, comprising: an execution unit executing a specific instruction set to access the first and the second memories; a first storage unit configured to store a first instruction set; a second storage unit configured to store a second instruction set; a selection unit outputting the first or the second instruction set to serve as the specific instruction set according to a control signal; and a processing unit generating the control signal according to an execution state of the execution unit.