Interface apparatus for coupling a minicomputer to a microcomputer for the transfer of data between them and method for using same

Claim 1

Interface apparatus for facilitating asynchronous parallel transfer of data at a speed of up to at least 1.6 megabits per second between a minicomputer and a microcomputer, said apparatus comprising a plurality of bidirectional data circuits parallel coupled between the computers for carrying data between the computers when either computer wants to send data to the other, and data transfer control circuit means coupled between the computers for permitting either computer, when it wants to send data, to: (a) indicate by means of a control signal to the receiving computer that the sending computer wants to transmit data over the data circuits, (b) resolve contention between the computers for access to the interface apparatus, (c) enable the receiving computer to indicate to the sending computer that the receiving computer is ready to receive data over the data circuits, (d) effect transfer of data from the sending computer to the receiving computer over the data circuits, and (e) enable the receiving computer to indicate to the sending computer that the receiving computer has received the data, said data transfer control means including: (A) a first circuit means coupled between the computers for receiving a first control signal from the microcomputer indicating that it wants to send data, which first control signal, as transmitted by said first circuit means, is readable by the minicomputer, (B) second circuit means coupled between the computers for receiving a second control signal from the minicomputer indicating that it wants to send data, which second control signal, as transmitted by said second circuit means, is readable by the microcomputer, (C) bistable circuit means coupled between the computers, said bistable circuit means including a bistable multivibrator which has a set input and which is preset to supply a "no" signal to the microcomputer indicating that no data is ready to be transmitted and, upon receiving a strobe signal from the minicomputer after the minicomputer has sensed that a first control signal is not present on said first circuit means and has then asserted a second control signal on said second circuit means and has presented data to said data circuits, then to provide a "yes" signal to the microcomputer indicating that data is ready to be transferred from the minicomputer to the microcomputer over said data circuits so that when the microcomputer reads the "yes" signal it can then input the data on said data circuits, (D) third circuit means coupled between the computers and to said bistable circuit means for carrying a reset signal from the microcomputer, indicating that it has input the data, to a reset input of said bistable multivibrator to reset same and to indicate to the minicomputer that the data has been received and input by the microcomputer, (E) fourth circuit means coupled between the computers for receiving a signal from the microcomputer and transmitting same to the minicomputer to indicate to the minicomputer that the microcomputer has data to send to the minicomputer, (F) fifth circuit means coupled between the computers and receiving a signal from the minicomputer indicating that the minicomputer is ready to receive data from the microcomputer and for transferring the signal to the microcomputer, and (G) AND circuit means coupled between computers and to said first circuit means and operable to receive the first control signal from the microcomputer at one input thereof which is coupled to said first circuit means and to receive a strobe signal at another input thereof from the microcomputer indicating that the microcomputer is ready to transmit data and upon receiving both signals to send a signal to the minicomputer that the data is ready to be transferred from the microcomputer to the minicomputer over the data circuits.