| 摘要 |
PURPOSE:To prevent an overrun of a selected input and output device, and to eliminate the need for a priority selecting circuit, by holding an input and output controller in a busy state until data transfer between the input and output device and a central processing unit ends. CONSTITUTION:When one of input and output devices 41-4n is selected, a corresponding FF in an input and output controller 3 is set, and whenever data transfer is held in readiness, the input and out device sends a data transfer request to the controller 3 to perform the data transfer between the memory in a central processing unit and the input and output device. When the data transfer ends, the completion of the interrupted data transfer is reported to the central processing unit 1 and the FF is reset. Even if the processing unit 1 indicates another input and output device selectively while said input and output device is selected, the FF in the controller 3 is set already, so the controller 3 sends a busy signal back to the central processing unit 1. |
