A processing system capable of connecting to a computer device comprising a second processing unit is provided. The processing system comprises a first processing unit and a first storage unit. The first storage unit is coupled to the first processing unit for storing at least a first programming code and a second programming code. At a first time point, the first processing unit accesses the first programming code from the first storage unit to set the processing system. At a second time point after the first time point, the first processing unit receives an instruction from the second processing unit and transfers the second programming code to the second processing unit in response to the instruction. The second processing unit controls the processing system with the second programming code.