A data processing circuit is described that includes an instruction decoder operable in a first and a second instruction mode. In the first instruction mode instructions have respective fields for controlling each of multiple functional units, and in the second instruction mode instructions controlling only one functional unit. A mode control circuit controls selecting the instruction modes. The instruction decoder uses time-stationary decoding of operations and destination registers. When instructions are scheduled, constraints are imposed on operations for which operation selection and destination register selection are included on different sides of an instruction mode change. When an instruction containing a jump is encountered, the mode control circuit sets the instruction mode for subsequent instructions in conformity with information provided by executing the jump command.