Digital Equipment Corporation

David P Rodgers

Richard Franklin Lary

William D Strecker

Thomas N Hastings

Steven H Rothman

Robert E Stewart

John V Levy

Richard J Casabona

David Potter

A digital data processing system with a central processor for responding to diverse instructions including instructions for calling subroutines. When the central processor executes a calling instruction, the central processor saves information corresponding to the operating environment for the calling routine and then utilizes corresponding information in the subroutine to establish the operating environment for the subroutine. A common return instruction at the completion of each subroutine causes the central processor to retrieve the saved operating information thereby to reestablish the operating environment for the calling routine.

Calling instructions for a data processing system

A digital data processing system including an interconnection for the various elements that constitute the system. Each element that connects to the interconnection is called a nexus. For one element to communicate with another element, the one element, as a commanding nexus, seeks control of the interconnection and then transmits a command and address of a storage location in the other element when it receives control of the interconnection. Control is then relinquished unless the one element is to send data to the other element whereupon the data is sent immediately. If data is to be retrieved, the other element retrieves the data, requests control of the interconnection and, when it receives control, transmits the data onto the interconnection with an identification of the one element. The one element then retrieves the data from the interconnection when it recognizes its own identification. If the other element is a memory element, it also contains storage file for storing commands and data if it already is operating in response to another element's command.

Data processing system with read operation splitting

A digital data processing system with a central processor for responding to diverse instructions characterized by having variable length. Each instruction includes an operation code. Certain instructions also include one or more operand specifiers. Each operand specifier can comprise one or more data bytes. Each instruction passes to an instruction buffer. Control circuitry in the central processor decodes the operation code and, in succession, each operand specifier byte. The operand specifiers and information derived from the operation code concerning each operand specifier are combined to obtain the address from which the operand is to be retrieved or to which an operand is to be transferred. Central processor response to an instruction for adding two addends located in first and second storage locations and storing the sum in a third location and instructions for calling a subroutine and returning from the subroutine to the calling routine are disclosed.

Central processor unit for executing instructions with a special operand

Central processor unit for executing instructions of variable length

Bus for a data processing system with overlapped sequences

A digital data processing system including an interconnection for the various elements that constitute the system. Each element that connects to the interconnection is called a nexus, and each nexus in the system can communicate with other nexuses on a priority basis. A central clocking circuit generates timing signals that control such communications by defining bus cycles on a synchronous basis and each nexus contains priority circuitry that operates in response to these signals. Each nexus that requires access to the interconnection asserts a transfer request signal at a predetermined time during each bus cycle. Priority arbitration circuitry in each nexus receives all such requests and samples them at another, later, time during each bus cycle. When a nexus is transmitting a request and no nexus with a higher priority is transmitting a request, that nexus takes control of the interconnection. A transfer during a subsequent bus cycle to another nexus can be prevented during certain types of transfers.

Distributed arbitration circuitry for data processing system

Growing community of inventors

Acton, MA, United States of America

David P Rodgers