Genrad, Inc.

Brian J Sargent

James K Skilling

Robert H Pincus

Rudy D Pietrantoni

Robert C Sullivan

An automatic circuit tester (10) employs a scanner (20) embodied in a group of interconnected scanner boards (46, 47) that provide switching by means of mechanical relays. The scanner boards plug simultaneously into respective instrument boards (44) and into a common scanner bus (50) separate from an instrument bus (38) that carries the signals that control the instruments on the instrument boards (44). The scanner bus provides a common pathway for signals to travel between instruments or system pins to which one scanner board is connected and those to which another is connected. It also provides scanner-control paths so that the instrument boards to which the scanner boards are connected to not need to provide such paths and thus do not need to be custom-designed for the particular tester in which they are used.

Automatic circuit tester with separate instrument and scanner buses

This apparatus controls the execution and content of computer programs in equipment containing a computer by causing the transfer of program data elements, including computer instructions, with a memory means of the apparatus, wherein the selection of data for transfer is effected either by the computer, operating in a normal manner, or by the apparatus, which may shift data selection between these two selection options so that the computer ceases selection of data constituting one program and begins selecting data of another program. While data elements are being transferred with the computer, other elements of the memory means are available for examination and modification such that new programs, the content of which may depend on the results of prior program execution, can be loaded, executed, and examined without interrupting, delaying, halting, or otherwise disturbing the instruction flow of the computer equipment.

Method of and apparatus for external control of computer program flow

A microprocessor-based system (10) is tested by a testing device (32) that substitutes instructions from a substitute memory (38) for those in the main memory (28) of the system (10) under test. When the processor (12) of the system under test attempts to read a location in its memory (28), it places signals on bus address lines (22) to designate the memory location and places a data-direction signal on a control line (50) to indicate that the memory (28) is to transmit rather than receive information. In ordinary operation, the memory then places its data on bus data lines (24). In order to replace the data from the main memory (28) with data from the substitute memory (38), the testing device (32) senses whether the address lines (22) carry the address of a memory location whose contents are to be substituted. When such an address is detected, it overdrives the control line (50) to cause it to indicate a write rather than a read. This prevents the main memory (28) from placing its data on the data lines (24). Instead, the test device (32) causes its substitute memory (38) to place its contents on the data lines (24). Since there is no contention between the substitute memory (38) and the main memory (28), the contents of the substitute memory (38) can be placed on the data lines (24) without overdriving them.

Method and apparatus for memory overlay

This apparatus controls the execution and content of computer programs in equipment containing a computer by causing the transfer of program data elements, including computer instructions, with a memory of the apparatus. The selection of data for transfer is effected either by the computer, operating in a normal manner, or by the apparatus, which may shift data selection between these two selection options so that the computer ceases selection of data constituting one program and begins selecting data of another program. While data elements are being transferred with the computer, other elements of the memory are available for examination and modification such that new programs, the content of which may depend on the results of prior program execution, can be loaded, executed, and examined without interrupting, delaying, halting, or otherwise disturbing the instruction flow of the computer equipment.

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Dunstable, MA, United States of America

Brian J Sargent