Abstract: 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.

Abstract: 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.

Abstract: 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.