A switched fabric is provided in a digital control system and data communication is performed using DMA transfer. A communication control unit is provided for controlling the switched fabric. The communication control unit determines the priorities of data to be transferred according to their types. When the communication control unit receives a request for higher-priority DMA transfer during DMA transfer, it suspends the current DMA transfer and performs the higher-priority DMA transfer. After completion of the higher-priority DMA transfer, the communication control unit resumes the suspended DMA transfer.