A method of half duplex transmission of a packetized digital data includes the steps of inputting a new packet to be transmitted to a first-in-first-out storage, determining whether the new packet contains time information related to synchronization with other electronic device, responsive to the determination that the new packet contains time information, updating a local timer of the electronic device with a prescribed value, continuously incrementing the local timer, responsive to a timing enabling transmission of the new packet by the transmitting/receiving unit of the electronic device, reading the new packet from the first-in-first-out storage, determining whether the new packet contains time information or not, changing the time information by using a value of the local timer to prevent mismatch in synchronization with other electronic device, and outputting to the bus through the transmitting/receiving unit.