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Register Numbering

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• Before you can make any sense out of the micro-programs, you need to know how each register is used.

  Recall the location of the registers in the datapath:

  

• The usage of each of the registers is as follows:

  Register	Name	Usage
  R0	Program Counter (PC)	Holds address of next instruction
  R1	Accumulator (AC)	Main working/scratch register
  R2	Stack pointer (SP)	Points to top of stack
  R3	Instruction Register (IR)	Holds currect instruction
  R4	Temp Instruction Register (TIR)	Use to decode instruction
  R5	0 (ZERO)	Hardwired Constant (like g0 in SPARC)
  R6	+1 (ONE)	Hardwired Constant (like g0 in SPARC)
  R7	-1 (MINUS ONE)	Hardwired Constant (like g0 in SPARC)
  R8	0000111111111111 (AMASK)	Used to extract 12 bit address from instruction
  R9	0000000011111111 (SMASK)	Used to extract 8 bit constant from instruction
  R10	A register	General Purpose register
  R11	B register	General Purpose register
  R12	C register	General Purpose register
  R13	D register	General Purpose register
  R14	E register	General Purpose register
  R15	F register	General Purpose register