| 摘要 |
PURPOSE:To use only one control signal line to facilitate miniaturizing a device and to simplify the circuit by providing an I/O device and a direct memory access control part with direction control circuits to control the direction of the control signal line. CONSTITUTION:An I/O device 1 and a direct memory access controller (DMAC) 2 are provided with direction control circuits 3-1 and 3-2 respectively. These circuits 3-1 and 3-2 have the same constitution, and the circuit 3-1 (3-2) consists of three-state gates 3-1-1 and 3-1-2 (3-2-1 and 3-2-2) and an FF 3-1-3 (3-2-3). When the I/O device 1 sends a request signal A, circuits 3-1 and 3-2 perform the control through three-state gates and FFs so that the signal flows on a control signal line 6 in the direction of arrows. When the DMAC 2 sends a confirmation response signal B, they perform the control so that the signal flows on the signal line 6 in the opposite direction. Thus, only one signal line 6 is used to miniaturize the device and the circuit is simplified. |
