SERIAL DATA TRANSMISSION METHOD AND SERIAL DATA TRANSMISSION APPARATUS

摘要

Data transmission and reception is effected via a data transmission line between a master device, which is capable of controlling data transfer, and a slave device in synchronism with a clock signal transmitted from the master device to the slave device via a clock transmission line. A signal indicative of the presence or absence of changes in the state of the slave device is sent to a third line connecting the master device to the slave device. The master device effects transmission for the purpose of acquiring data concerning state changes on the slave device side when the signal of the third line indicates that a state change has taken place on the slave device side. The transmission load can be reduced by effecting transmission used by the master device to check data representing the state of the slave device only when necessary.