Consider a machine that brings all the operands to registers before performing the ALU operation. The machine uses PC, IR, and MAR registers. All memory accesses bring data to the AX register. The operations are performed in AC and AX registers, and results are stored in the AC register. List and explain all the microoperations required to execute an instruction AC AC+[MAR] on this machine

To execute the instruction ( AC \leftarrow AC + [MAR] ) on the given machine, we need to perform several microoperations.

Here’s a list and explanation of each microoperation:

1. Fetch Instruction:

• Fetch the instruction from memory using the Program Counter (PC).
• PC points to the memory address of the instruction to be fetched.
• Load the instruction into the Instruction Register (IR).

1. Decode Instruction:

• Decode the instruction in the Instruction Register (IR) to determine the operation to be performed.
• Determine that the instruction is of the form ( AC \leftarrow AC + [MAR] ).

1. Calculate Memory Address:

• Calculate the memory address to be accessed using the Memory Address Register (MAR).
• The memory address is typically provided directly by the instruction or calculated based on addressing modes.

1. Read Operand from Memory:

• Transfer the content of memory addressed by the Memory Address Register (MAR) to the AX register.
• Load the operand from memory into the AX register.

1. Perform Addition:

• Perform addition operation between the content of the AC register and the content of the AX register.
• Store the result of the addition operation in the AC register.

1. Store Result:

• Store the result of the addition operation from the AC register back to memory, if required.
• This step is not explicitly mentioned in the instruction ( AC \leftarrow AC + [MAR] ), but if the result needs to be stored back in memory, this step is necessary.

Explanation:

• The machine follows a load-store architecture, where data is first loaded into registers, manipulated, and then stored back if necessary.
• The Program Counter (PC) is used to fetch instructions from memory.
• The Instruction Register (IR) holds the current instruction being executed.
• The Memory Address Register (MAR) is used to hold the memory address to be accessed.
• The AX register serves as a temporary storage for operands fetched from memory.
• The AC register is used for arithmetic and logical operations.
• The microoperations ensure that the instruction ( AC \leftarrow AC + [MAR] ) is executed correctly by fetching the operand from memory, performing the addition operation, and storing the result back if necessary.