DATA TRANSFER SYSTEM

PROBLEM TO BE SOLVED: To reduce the burden of a CPU on each substrate and to reduce costs for a data transfer system by making data transfer lines from a high-order substrate to plural low-order substrates into one common line and providing communication request processing parts in the same configuration on the high-order substrate and the respective low-order substrates. SOLUTION: Between a communication request processing part 15 of a high-order substrate 10 and communication request processing parts 25-35 of respective low-order substrates 1-N, control lines α1 -αN and β1 -βN are provided for letting flow transmission request signals (REQ) and response permit signals (ACK). In this case, the control lines α1 -αN for sending control signals from the high-order substrate 10 to the respective low-order substrates 1-N are respectively independent control lines and the control lines β1 -βN for sending control signals from the low-order substrates 1-N to the high- order substrate 10 are respectively independent control lines as well. Thus, since transmission is controlled by the control signals while providing the communication request processing parts in the same quality on the high-order substrate 10 and the low-order substrates 1-N, bidirectional data transfer is enabled without loading any burden to CPU 11 and 21-31 on the high-order substrate 10 and the low-order substrates 1-N.