Abstract: An instruction execution modification mechanism is described for a digital data processor wherein multiple programs or tasks are performed in a concurrent manner by means of a time slice mechanism which causes the instructions from the different programs to be executed in an interleaved manner. Instructions from the different programs are executed during different successive time slice intervals. The instruction execution modification mechanism is responsive to the occurrences of various predetermined conditions in the data processing system for selectively modifying the normal execution of different ones of the instructions in different ones of the programs. To this end, there is provided a program list mechanism listing the modifiable programs, an instruction list mechanism listing the modifiable instructions and a modification storage mechanism for storing modification signals for the different instructions.

Abstract: A method for performing manual operations, such as address compare equal stop, single cycle alter, etc., in a time slice controlled microprocessor with microprogramming, which avoids stopping the processor clock when any of the programs requires a manual operation. This problem is solved by assigning the manual operations to a specific program, which for the other programs in the multiprogram environment executes the manual operations required.