JPH034942B

PURPOSE:To lessen the capacity of the buffer of a file adapter and to generate the request signals of the I/O controller beyond the buffer capacity by setting the buffer capacity and the permissible maximum number of the request signals separately. CONSTITUTION:A file adapter 2 which as a buffer function is connected between its main memory 1 and an I/O controller 3 to constitute a data transmission controlling system. To this adapter 2, a buffer 4, an overrun display FF5, an overrun detecting circuit 6, and an acknowledge signal generator 7 are provided. In case when data is transmitted from this adapter 2 to the device 3, a request signal REQ is transmitted from the device 3. Responding to the signal REQ, an acknowledge signal ACK and the data are outputted by the adapter 2. At this time,when the data does not exist in a buffer 4, the FF5 becomes on, and a pseudo data is transmitted. And, the buffer capacity of the adapter 2 and the permissible maximum number of the signals ACK of the device 3 are separately set, to generate the ACK signal beyond the buffer capacity.