Abstract: An improved data processor control subsystem in which a cycle counter having a plurality of cascade-connected stages also comprises one or more supplemental or dummy stages, which can be selectively inserted or removed from the chain of cascade-connected stages, to alter the number of sub-cycles in an operating cycle, thereby decreasing the complexity of associated decoding circuitry.

Abstract: In executing and controlling internal data flow for a particular program, it is often necessary to delay execution of an instruction by the insertion of an appropriate number of wait cycles. Thus, it may be necessary to interrupt instruction execution, for example, to insert a given number of wait cycles for channel access to common storage of the data processing system, for reloading a data or instruction buffer, or for a like situation. In such cases, the control unit has to ignore the particular instruction awaiting execution and execute another forced operation instead.An appropriate code is provided for a NO OPERATION instruction, say all bits zero. When a forced operation is to be executed, this code can be generated with fewer logic means at the output of the instruction register. As a result, there are no control signals active at the output of the decoder. The signals indicating forced operations have to be considered by the decoder only if a control signal is to be generated.