Data processing system with unique microcode control

Claim 1

In a data processing system including processor means for processing said data, memory means for storing said data and for storing instructions for directing operation of said system, and bus means for conducting said data and said instructions between said memory means and said processor means, said processor means comprising: CPU processor means connected to said bus means for performing arithemetic and logical operations upon said data, and microcode control means connected from said bus means and responsive to said instructions for providing sequences of microinstructions for controlling said operations of said system said microcode control means being adapted to be responsive to said operations of said system and to select subsequences of microinstructions in response thereto, means connected from said bus means for receiving said instructions, means connected from other portions of said system for receiving information regarding state of said operations of said system, microcode memory means for storing and providing said sequences of microinstructions, and microcode sequence control means responsive to said received instructions and to said state of operations information for providing to said microcode memory means addresses for selecting said sequences of microinstructions, said microcode sequence control means comprising: sequence control internal microcode control means responsive to operation of said sequence control means and to said microinstructions and to said state of operation information for providing signals for controlling operation of said sequence controller means, register means connected from said instruction receiving means and said state receiving means and responsive to said sequence control internal microcode control means for receiving and storing an initial address of a presently selected one of said microinstruction sequences, microcode program counter means connected to said register means and responsive to said sequence control internal microcode control means for receiving said initial address and providing successive said addresses of said presently selected one of said microinstruction sequences, address multiplexor means connected from said register means and said microcode program counter means and said sequence control internal microcode control means for providing said addresses to said microcode memory means, and microcode state save means, including microcode state register means, connected from said sequence control means and responsive to said sequence control internal microcode control means for receiving said storing and address and start of execution of a presently executing microinstruction, and microcode stack means having inputs connected from said microcode state save means and outputs connected to said address multiplexor means for saving and restoring state of execution of interrupted ones of said microinstructions.