4980821 : Stack-memory-based writable instruction set computer having a single data bus

What we claim is:

• 1. A writable instruction set computer for use with a host computer having user input/output means for inputting individual command signals, said writable instruction set computer comprising:
  • a single data bus means;
  • addressable and writable main program memory means coupled to said bus means for storing data from and loading stored data onto said bus means;
  • addressable and writable microprogram memory means coupled to said bus means for storing microcode;
  • microinstruction register means coupled to said microprogram memory means and to said bus means for storing microinstructions output from said microprogram memory means;
  • arithmetic logic unit means coupled to said bus means for performing operations on data as defined by microcode stored in said microprogram memory means;
  • stack memory means coupled to said bus means for storing temporarily information used during program execution independent of said main memory means;
  • clock means for generating a single-cycle clock signal for each individual command signal transmitted from the host computer to said clock means;
  • execution control logic means, responsive to the clock signal and coupled to said bus means, for performing a single data transfer on said bus means for each clock signal cycle, and for executing a single operation, defined by a microprogram instruction, for each discontinuous single-cycle clock signal; and
  • interface means coupled to said bus means and to said clock-signal generating means for connecting said bus means to the host computer for inputting microinstructions from the host computer directly into said microinstruction register means via said bus means for executing the microinstructions stored in said microinstruction register means in a single-step mode.
• 2. A writable instruction set computer comprising:
  • a single data bus means;
  • addressable and writable main program memory means coupled to said bus means for storing data from and loading stored data onto said bus means;
  • addressable and writable microprogram memory means coupled to said bus means for storing microcode, including instructions comprising only one of an opcode and a subroutine address, wherein opcodes are identified by a plurality of bits of a word, which bits have predetermined values, thereby leaving other values of those bits for specifying subroutine addresses;
  • arithmetic logic unit means coupled to said bus means for performing operations on data as defined by microcode stored in said microprogram memory means;
  • stack memory means coupled to said bus means for storing temporarily information used during program execution independent of said main memory means;
  • clock means for generating a cyclic clock signal; and
  • execution control logic means, responsive to the clock signal and coupled to said bus means, for performing a single data transfer on said bus means for each clock signal cycle.