8051 Microcontroller Interview Q&A: Top 10 Questions

Here are 10 frequently asked interview questions, along with detailed answers, about the 8051 microcontroller. This guide is designed to help you ace your job interview for 8051-related positions and will also be a helpful resource for engineering students during viva exams.

Question 1: What is the 8051 microcontroller?

Answer: The 8051 is an 8-bit microcontroller that Intel developed in 1980. It’s based on the Harvard architecture and is widely used in embedded systems. It boasts a rich instruction set, built-in peripherals, and is well-regarded for its simplicity and reliability.

Question 2: Describe the architecture of the 8051 microcontroller.

Answer: The 8051’s architecture includes:

• An 8-bit Arithmetic Logic Unit (ALU).
• An 8-bit accumulator (A) and an 8-bit B register.
• 128 bytes of internal RAM.
• 4KB of on-chip ROM.
• Four 8-bit parallel I/O ports.
• Two 16-bit timers/counters.
• A serial communication port (UART).
• An interrupt control unit.

The 8051 uses a Harvard architecture, which means it has separate address spaces for program and data memory. This allows the microcontroller to fetch instructions and data simultaneously, increasing processing speed.

Question 3: What are the key features of the 8051 microcontroller?

Answer: The key features of the 8051 include:

• 4KB on-chip ROM for program storage.
• 128 bytes on-chip RAM for data storage.
• Four parallel I/O ports, each 8 bits wide.
• Two 16-bit timers/counters.
• Full-duplex UART for serial communication.
• Five interrupt sources.
• Bit and byte addressable RAM.
• Boolean processor (for bit-level operations).

Question 4: How does the 8051 handle interrupts?

Answer: The 8051 has five interrupt sources:

1. Two external interrupts (INT0 and INT1).
2. Two timer interrupts (Timer 0 and Timer 1).
3. One serial communication interrupt.

Each interrupt can be enabled or disabled individually using the IE (Interrupt Enable) register. When an interrupt occurs, the microcontroller uses a vector table to jump to the appropriate interrupt service routine (ISR). This ensures that the correct code is executed in response to the interrupt.

Question 5: What are SFRs in the 8051 microcontroller?

Answer: Special Function Registers (SFRs) are a set of registers used to control various functions of the microcontroller. They’re located in the address range of 80H to FFH. SFRs are used to configure I/O ports, timers, serial communication, and interrupts, among other things. Essentially, they’re the control panel for the 8051’s peripherals.

Question 6: Explain the use of the accumulator in the 8051 microcontroller.

Answer: The accumulator, often denoted as A, is an 8-bit register central to arithmetic and logical operations in the 8051. It serves as the primary register for data manipulation. The results of most arithmetic and logic operations are stored in the accumulator, making it a vital component for processing data.

Question 7: What is the function of the PSW register in the 8051?

Answer: The Program Status Word (PSW) register is an 8-bit register that holds the status of the CPU. It contains various flags, including:

• Carry (CY)
• Auxiliary Carry (AC)
• Parity (P)
• Overflow (OV)

These flags indicate the outcome of operations, such as whether a carry was generated or the parity of the result. They allow the microcontroller to make decisions based on the results of previous calculations.

Question 8: How does the 8051 perform serial communication?

Answer: The 8051 has a built-in UART (Universal Asynchronous Receiver/Transmitter) for serial communication. It uses the SCON (Serial Control) and SBUF (Serial Buffer) registers to manage data transmission and reception.

The microcontroller supports various modes of operation, including:

• 8-bit UART
• 9-bit UART
• Multi-processor communication

This allows the 8051 to communicate with other devices over a serial connection.

Question 9: Describe the role of timers in the 8051 microcontroller.

Answer: The 8051 has two 16-bit timers/counters (Timer 0 and Timer 1) that can operate in several modes. They can be used as:

• Timers to generate time delays.
• Counters to count external events.

The timers can be programmed to operate in different modes, such as:

• 13-bit mode
• 16-bit mode
• Auto-reload mode

This flexibility makes them useful for a variety of timing and counting applications.

Question 10: What is the function of the DPTR register in the 8051?

Answer: The Data Pointer (DPTR) register is a 16-bit register used to store the address of data in external memory. It’s commonly used for accessing external data memory and program memory. The DPTR consists of two 8-bit registers: DPH (high byte) and DPL (low byte). It provides a way to access a larger memory space than can be addressed directly.