Electronics Engineering (ELEX) Board Practice Exam

Which process does the term 'opcode fetch' refer to in microprocessor operations?

1. Reading data from memory

2. Storing results in memory

3. Retrieving machine code for execution

4. Writing data to an input/output device

The correct answer is: Retrieving machine code for execution

The term 'opcode fetch' specifically refers to the process where the microprocessor retrieves the machine code instruction, also known as the opcode, from memory in order to execute it. This process is integral to how a microprocessor functions, as it represents the first step in instruction execution. When a program is run, the processor continuously fetches these opcodes from memory, interprets them, and performs the corresponding operations defined by the instruction set architecture. Retrieving the opcode is essential for the execution of the program, since each opcode corresponds to specific operations, such as arithmetic computations, logic operations, or control functions. Once the opcode is fetched, the microprocessor can then decode and execute the instruction, which might involve reading or writing data or interacting with input/output devices, but the fetching itself is purely about obtaining the opcode.