| 摘要 |
PURPOSE:To discriminate the mode of a transfer request signal, by making a counter counter counting operation by a read or write signal, and comparing the counted number with a data transferred number. CONSTITUTION:When a data transfer request signal DRQ, write signal W, or read signal R is impressed upon an interface controlling device 2, a counter 10 makes count-up. In the case of first-in-first-out mode (FiFo mode), therefore, an input-output device operates under the FiFo mode when the number of data transfer byte is many, by comparing the data transfer byte number with the counted value of the counter 10. Moreover, under a normal mode, the number of times of the data transfer request signal DRQ is reduced to the same as the number of data transfer bytes. Therefore, the counted value of the counter 10 becomes the same as the number of data transfer bytes and, by comparing them with each other in the same way, the transfer mode is discriminated.
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