Synchronous/asynchronous data bus with message priority handling capability and segmented memory transfer

摘要

A data transfer appts. employing a data buse having synchronous and asynchronous modes for communication between a first and second memory units. It determines a need for memory transfer and responsively searches a number of memory segments in the second memory for a valid data record stored in one of the segments. The memory transfer device then communicates the valid data record from the second data unit to the first memory unit in the asynchronous mode when the search finds a valid data record. It communicates an empty data record in the asynchronous mode when the search does not find a valid data record.