Abstract: A method of controlling data sending and receiving operations between two microprocessors, in which a second controlled-side microprocessor receives a selected signal which is one of a data sending request signal and a data receiving request signal from a first controlling-side microprocessor and the second microprocessor also receives a resultant select signal produced by a logical OR operation on both request signals and determines if the selected signal indicates a "receiving request" or a "sending request" at the same time that it responds to the resultant select signal, thereby executing the requested operation. Hence, even if the second microprocessor does not receive the resultant select signal and the sending/receiving signal at the same time, the second microprocessor can determine simultaneously with the receipt of the resultant select signal if it should send or receive the data, resulting in high-speed data processing.