| 摘要 |
PURPOSE:To utilize a re-transmission request signal line to make a cancel signal line needless when an access request issued previously from a data transmission-side processing unit is cancelled in the advance control system of the I/O system of the data processing system. CONSTITUTION:When the priority level determination between channel unit CU8-0 and other CUs in UI (unit interface) unit 7-0 which accepted request RQ from CU8-0 results in selecting CU8-0, unit 7-0 issues request REQ' to BI (bus interface) unit 6. Unit 6 determines a priority level and selects unit 7-0. CU8-0 performs advance control by transmitting address information and data. When an error exists in address information, etc., unit 6 issues a re-transmission request through re-transmission request signal line 9-0. Unit 7-0 checks the validity of data which is accepted at timing T6; and in case of error, unit 7-0 issues a cancel signal for cancelling request REQ' through signal line 9-0 as shown by the thick-line arrow. As a result, the number of signal lines can be reduced, and the transfer processing time can be obtained. |
