| 摘要 |
To avoid interruptions of continuous data transfers through the input-output units (M1 to Mn) of a common data line system (Z-BUS) which are caused by data units which are not available at the right time because of delayed acceptance of a request (Mn.LPREQ) by the central control unit (BUMA), the requests are made with varying priority (LP or HP) depending on the urgency of the data transfer to be carried out, and as the waiting time for acceptance of a request increases, its priority is changed with increasing urgency from step to step. For instance, two individual request lines (Mn.LPREQ and Mn.HPREQ), which have different priorities per input-output unit (e.g. Mn), and which are released depending on the degree of fullness of the available buffer memory (BUF). Additional common control line (Z.HOLDREQ) for all input-output units (M1 to Mn), for switching the particular request to effective, or changing it, and for resetting an accepted request. <IMAGE>
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