ITPEC FE Morning April 2021 Question 11

Program counter (PC) — it holds the address of the next instruction and advances after each fetch, or is reloaded by a jump.

In the fetch cycle the CPU reads the instruction at the address in the program counter into the instruction register, then updates the program counter to point to the following instruction. A branch or jump works by writing a new address into the program counter.

Answer (b)

Why not others:

• •(a) Accumulator — holds operands and the results of arithmetic and logic operations, not instruction addresses
• •(c) Stack pointer — holds the address of the top of the stack, used by push, pop, and subroutine calls and returns
• •(d) Timer — counts time and raises interrupts at set intervals; it plays no part in locating the next instruction

Key rule: The program counter says where the next instruction is; the stack pointer says where the top of the stack is.

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