GATE EC 2016 Set 1 — Question 54

MCQ+2 / -0.67MediumMachine Instructions & AddressingComputer OrganizationDigital Circuits

Digital Circuits → Computer Organization → Machine Instructions & Addressing

Last updated 5 September 2026

Question

In an 8085 system, a PUSH operation requires more clock cycles than a POP operation. Which one of the following options is the correct reason for this?

Correct answer (C) The stack pointer needs to be pre-decremented before writing registers in a PUSH, whereas a POP operation uses the address already in the stack pointer. Solution In the 8085 microprocessor, a PUSH instruction (e.g., PUSH B) takes 12 T-states, while a POP instruction (e.g., POP B) takes 10 T-states. The difference lies in the opcode fetch machine cycle. For PUSH, the opcode fetch cycle is 6 T-states because it includes internal operations to decrement the stack pointer (SP) before the first memory write. For POP, the opcode fetch cycle is 4 T-states because the SP is used as is for the first memory read, and incremented afterwards. Thus, the pre-decrement requirement in PUSH adds extra clock cycles. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

Review answer and solution without JavaScript

Interactive answer checking needs JavaScript. The published solution is available below.

Correct answer (C) The stack pointer needs to be pre-decremented before writing registers in a PUSH, whereas a POP operation uses the address already in the stack pointer. Solution In the 8085 microprocessor, a PUSH instruction (e.g., PUSH B) takes 12 T-states, while a POP instruction (e.g., POP B) takes 10 T-states. The difference lies in the opcode fetch machine cycle. For PUSH, the opcode fetch cycle is 6 T-states because it includes internal operations to decrement the stack pointer (SP) before the first memory write. For POP, the opcode fetch cycle is 4 T-states because the SP is used as is for the first memory read, and incremented afterwards. Thus, the pre-decrement requirement in PUSH adds extra clock cycles.

Continue learning with Success Tracker

Use Success Tracker to ask about the reasoning, then try another GATE EC question to check your understanding.

AI-powered practice· Unlimited practice on eligible plans

PYQs with solutions: Attempt available previous-year questions, then compare your reasoning with the worked solution. Coverage varies by stream.
Practice that adapts: Choose a topic, work on weaker areas and bookmark questions to revisit. Your attempts feed your progress tracking.
AI doubt support: Ask follow-up questions about a step or concept while practising, instead of stopping at the final answer.

Unlimited practice is available on eligible plans. Free practice and AI usage have limits; check the current plan allowances before choosing.

This page stays readable without an account. AI responses can be wrong; check them against the solution and source material.