Consider the following sequence of micro operations :

MBR ← PC

MAR ← X

PC ← Y

MEMORY ← MBR

Which one of the following is possible operation performed by this sequence ?

The correct answer is Instruction Fetch.

Key Points

• Instruction fetch is the process of reading an instruction from memory into the processor.
• The sequence of micro-operations given corresponds to the steps involved in fetching an instruction from memory:
  • MBR ← PC: The content of the Program Counter (PC) is transferred to the Memory Buffer Register (MBR).
  • MAR ← X: The content of the register X is transferred to the Memory Address Register (MAR).
  • PC ← Y: The content of the register Y is transferred to the Program Counter (PC).
  • MEMORY ← MBR: The content of the MBR is transferred to the memory.
• This sequence is typical of the steps taken to fetch an instruction from memory, making instruction fetch the correct answer.

Additional Information

• The Program Counter (PC) holds the address of the next instruction to be fetched.
• The Memory Address Register (MAR) holds the address of the memory location to be accessed.
• The Memory Buffer Register (MBR) holds the data to be written to memory or the data read from memory.
• Fetching an instruction involves reading the instruction from memory into the instruction register.
• This process is crucial for the CPU to understand which operation to execute next.