Memory reference instruction

Memory reference instruction

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  The basic computer has 16-bit instruction register (IR) which can denote either memory reference or register reference or input-output instruction.
  
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  Memory Reference – These instructions refer to memory address as an operand. The other operand is always accumulator. Specifies 12-bit address, 3-bit opcode (other than 111) and 1-bit addressing mode for direct and indirect addressing.
  
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  Example – IR register contains = 0001XXXXXXXXXXXX, i.e. ADD after fetching and decoding of instruction we find out that it is a memory reference instruction for ADD operation.
  
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  Hence, DR ← M[AR] AC ← AC + DR, SC ← 0
  

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