A data communication system is provided. The data communication system includes a main processor, and at least one sub-processor or at least one peripheral device connected with the main processor according to a serial peripheral interface (SPI) method and performing an operation corresponding to a command transferred from the main processor. The connection according to the SPI method is made by one or more bus lines including a master in slave out (MISO) line and master out slave in (MOSI) line, a slave select (SS) line, an interrupt line, and a clock transfer line.