ISRO | ISRO CS 2020 | Question 14

Statements associated with registers of a CPU are given. Identify the false statement.
(A) The program counter holds the memory address of the instruction in execution.
(B) Only opcode is transferred to the control unit.
(C) An instruction in the instruction register consists of the opcode and the operand.
(D) The value of the program counter is incremented by 1 once its value has been read
to the memory address register.


Answer: (D)

Explanation:

  • Program counter (PC) holds memory address of the instruction in execution and memory address of the next instruction to be fetched.
  • During the instruction fetch, an opcode is put into the IR (opcode), and is decoded by the control unit.
  • An instruction format defines the different component of an instruction. The main components of an instruction are opcode (which instruction to be executed) and operands (data on which instruction to be executed).
  • The value of the program counter is incremented by 1 once (only of instruction size is 1 word) its value has been read to the memory address register.

So, option (D) is false.

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