This question was asked inGPSC Deputy Executive Engineer (Electrical) Class-2 Master Paper 2026Question 139 of 195 published · Gujarat Public Service CommissionOpen paper
Q139Easy8051 Microcontroller

Consider the following statements regarding Memory interfacing in 8051:
1. Address decoding is required for memory interfacing.
2. Chip select signal is used to enable memory device.
3. Multiple devices can share data bus.
Which of the above statements is/are correct?

Answer & step-by-step solution
Correct answer: B. 1, 2 and 3
Quick explanation

The classic 8051 is an 8-bit Harvard-style microcontroller with separate code and data spaces. The standard core has 4 KB on-chip program ROM and 128 bytes internal RAM, supports external memory, multiple interrupts and configurable interrupt priority. Key relation: Reset SP=07H; classic internal RAM=128 bytes; standard ROM=4 KB.

Exam focus: Remember 07H for stack pointer reset. Common trap: 00H is not the reset value of the 8051 stack pointer.

Reset SP=07H; classic internal RAM=128 bytes; standard ROM=4 KB.

Statement-wise Verification

  • Statement 1 - Correct.
    Address decoding is required for memory interfacing.
    The standard core has 4 KB on-chip program ROM and 128 bytes internal RAM, supports external memory, multiple interrupts and configurable interrupt priority.
  • Statement 2 - Correct.
    Chip select signal is used to enable memory device.
    The standard core has 4 KB on-chip program ROM and 128 bytes internal RAM, supports external memory, multiple interrupts and configurable interrupt priority.
  • Statement 3 - Correct.
    Multiple devices can share data bus.
    The classic 8051 is an 8-bit Harvard-style microcontroller with separate code and data spaces.

Core Concept

The classic 8051 is an 8-bit Harvard-style microcontroller with separate code and data spaces. The standard core has 4 KB on-chip program ROM and 128 bytes internal RAM, supports external memory, multiple interrupts and configurable interrupt priority. On reset the stack pointer is 07H, so the first PUSH stores at 08H.

Formula / Key Relationship

Reset SP=07H; classic internal RAM=128 bytes; standard ROM=4 KB.

Why the Other Options Are Wrong

Option A is incorrect because it omits correct statement(s) 3. Option C is incorrect because it omits correct statement(s) 2. Option D is incorrect because it omits correct statement(s) 1.

Exam Shortcut / Approach

Remember 07H for stack pointer reset.

Common Mistake

00H is not the reset value of the 8051 stack pointer.

Quick Revision

Address Decoding Chip Select and Shared Data Bus is linked with Memory Interfacing, 8051 Interfacing and Microprocessors and Microcontrollers. Remember 07H for stack pointer reset.

Exam tipRemember 07H for stack pointer reset.
Verified · SRO editorial desk Report
Try it before reading the solution — tap an option.0/1✓ 0✗ 0

More 8051 Microcontroller questions