ITPEC FE Morning April 2023 Question 11
When a CPU has a special register used in push and pop instructions, which of the following is an appropriate term for this register?
Explanation
Stack pointer — the register that holds the address of the top of the stack.
A push stores a value at the top of the stack and moves the stack pointer to the new top; a pop reads the top value and moves the pointer back. Subroutine calls and interrupts use the same mechanism to save return addresses and register contents.
Answer (c)
Why not others:
- •(a) Instruction register — holds the instruction currently being decoded and executed
- •(b) Program counter — holds the address of the next instruction to fetch
- •(d) Status register — holds condition flags such as zero, carry, sign and overflow
Key rule: Each special register has one job: the program counter says where the next instruction is, the instruction register what is running now, the stack pointer where the stack top is, and the status register what the last operation produced.
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