THE UNIVERSITY OF MICHIGAN, Technical Report 12
Original Publication Date: 1968-Nov-01
Included in the Prior Art Database: 2005-Sep-15
Software Patent Institute
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The principal function of the interface is to transfer blocks of data from the memory of either computer to the memory of the other. Once initialized, the interface transfers data via cycle-steal with respect to each of the two computers' memories. Either computer can detect the status of the interface at any time during a data transfer, and can halt or modify the operation as desired. When a transfer operation has been completed, the interface can signal either or both computers. Special circuitry permits resolution of conflicts resulting from simultaneous attempts by both computers to use the interface. Provision is also included for direct signaling of either computer by the other, via an ";interruption.";. The operation of the interface during data-transfers is completely controlled by registers internal to itself which can be loaded by either computer; and the condition of the data-handling circuits is indicated at all times by these same registers, which can also be read by either computer. This allows the interface to be commanded fully by either computer or by both. The use of addressable registers to control the interface permits considerable and unusual flexibility in its operation. Independent counters govern a parallel-to-serial-to-parallel data path via a shift register. This allows flexible control of data density and format. This feature permits efficient use of data storage devices (including the computers' own memories), and is especially desirable when the two computers differ in memory word size as in this case.