Image Number 7 for United States Patent #4556938.
A microcode control mechanism is provided for producing the sequences of microwords used to control the execution of processor instructions in a microprogrammed data processor. This microcode control mechanism includes sequence counter circuitry for supplying a sequence of numbers and a programmable logic array mechanism responsive to the processor instruction and to the sequence of numbers for producing a sequence of microwords needed to execute the instruction. The microcode control mechanism also includes repeat circuitry responsive to a predetermined microword produced by the programmable logic array mechanism for setting the sequence counter circuitry back to a count which is less than the current count for causing a selected portion of the microword sequence to be repeated. The microcode control mechanism further includes a programmable repeat counter for counting the number of times the selected portion is repeated and for disabling the repeating action after a selected number of repeats.