In the disclosure, a data processing system includes a microprocessor and a memory. The integrity of data read from a memory by a microprocessor may be checked. When an instruction address is transmitted from the microprocessor to the memory for reading the instruction data corresponding to the instruction address, predetermined dummy data is also read from the memory while the instruction data is read. The integrity of the instruction data may be check by comparing the predetermined dummy data to a hardwire data that is not stored in the memory. If the dummy data matches the hardwire data, the instruction data read from the memory is determined to be correct.