A control unit uses a micro-coding scheme to control the CPU. Which of the follo

Question

A control unit uses a micro-coding scheme to control the CPU. Which of the following is/are true of the microcoding scheme?

I. Variations of instructions must share a common control sequence otherwise the memory will grow too large.

II. Variations within a particular instruction such as “ADD” include, or are caused by, different addressing modes used and varying operands.

III. The IR feeds a look up table which determines where the micro-program instruction sequence begins.

a I, II and III

b I only

c II only

d III only

e None of the above

Explanation / Answer

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I. Variations of instructions must share a common control sequence otherwise the memory will grow too large.
II. Variations within a particular instruction such as “ADD” include, or are caused by, different addressing modes used and varying operands.
III. The IR feeds a look up table which determines where the micro-program instruction sequence begins.

a I, II and III
b I only
c II only
d III only
e None of the above

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Answer:
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   a I, II and III

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Explanation:
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   I. Variations of instructions must share a common control sequence to utilize the memory in efficient manner.
   II. Add instruction is used by many of addressing mode such register addressing mode where the counter is being used and incremented over the stack operations.
   III. IR stands for instruction register (IR) is the part of a CPU's control unit that stores the instruction currently being executed or decoded. Which determines the micro-program instruction sequence begins.
  
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