8051 Microcontroller Interview Questions with Answers

Practice here the most popular 8051 Microcontroller Interview Questions and Answers, that are very important for freshers candidates.

Q1. What is an 8051 microcontroller?
A1. The 8051 microcontroller is an 8-bit microcontroller that was originally introduced by Intel. It is widely used in various embedded systems due to its simplicity, low cost, and availability.

Q2. What are the key features of the 8051 microcontroller?
A2. The key features of the 8051 microcontroller include:

• 8-bit CPU architecture
• 128 bytes of on-chip RAM
• 4 KB of on-chip ROM/program memory
• Four 8-bit I/O ports
• Two 16-bit timer/counters
• Serial communication interface
• Interrupt system

Q3. Explain the different memory spaces in the 8051 microcontroller.
A3. The 8051 microcontroller has three memory spaces:

• Program memory (ROM): It stores the program code to be executed.
• Data memory (RAM): It is used to store data during program execution.
• Special Function Register (SFR) memory: It consists of various control and data registers used to interface with peripherals.

Q4. What is the maximum amount of external RAM that can be interfaced with the 8051 microcontroller?
A4. The 8051 microcontroller can address a maximum of 64 KB of external RAM.

Q5. Explain the difference between RISC and CISC architectures.
A5. RISC (Reduced Instruction Set Computer) architecture uses a simplified set of instructions with a fixed length, executing them in a single cycle. CISC (Complex Instruction Set Computer) architecture supports complex instructions, often of variable length, which may require multiple cycles to execute.

Q6. How many interrupt sources does the 8051 microcontroller have?
A6. The 8051 microcontroller has five interrupt sources: External 0 (INT0), External 1 (INT1), Timer 0 (TF0), Timer 1 (TF1), and Serial Port (RI/TI).

Q7. What is the size of the register bank in the 8051 microcontroller?
A7. The 8051 microcontroller has four register banks, each containing eight registers. Each register is 8 bits wide.

Q8. Explain the difference between MOV and MOVC instructions.
A8. The MOV instruction is used to transfer data between registers or between a register and a memory location. The MOVC (Move Code) instruction is used to move a byte from the program memory (ROM) to a register.

Q9. What is the function of the ALE pin in the 8051 microcontroller?
A9. The ALE (Address Latch Enable) pin is used to demultiplex the address and data bus during external memory access. It indicates that the address is stable on the bus and the data can be read or written.

Q10. How can you generate a delay in the 8051 microcontroller?
A10. To generate a delay, the 8051 microcontroller can utilize timers or software loops. By configuring the timer registers and using appropriate delay calculation formulas, precise delays can be achieved.

Q11. Explain the concept of bit-addressable memory in the 8051 microcontroller.
A11. The 8051 microcontroller provides bit-addressable memory, which means that individual bits in the RAM can be accessed and manipulated directly. This allows efficient control over individual bits without affecting the rest of the byte.

Q12. What is the function of the PCA (Programmable Counter Array) module in the 8051 microcontroller?
A12. The PCA module in the 8051 microcontroller is used for pulse width modulation (PWM) and timing operations. It provides two 16-bit PWM channels and can generate hardware interrupts based on timer overflow or comparator values.

Q13. What is the role of the PCON register in the 8051 microcontroller?
A13. The PCON (Power Control) register in the 8051 microcontroller is used for power management. It contains control bits for controlling the microcontroller's power modes, such as idle mode and power-down mode.

Q14. Explain the difference between a hardware interrupt and a software interrupt.
A14. A hardware interrupt is triggered by an external event, such as a signal on an interrupt pin or a timer overflow. A software interrupt, also known as a software interrupt, is triggered by a specific instruction in the program code.

Q15. What is the function of the SBUF register in the 8051 microcontroller?
A15. The SBUF (Serial Buffer) register is used for serial communication in the 8051 microcontroller. It holds the data to be transmitted or received via the serial port.

Q16. How can you enable and disable interrupts in the 8051 microcontroller?
A16. Interrupts can be enabled or disabled by setting or clearing the appropriate bits in the Interrupt Enable (IE) register. By setting the corresponding bit, a specific interrupt source can be enabled, and by clearing the bit, it can be disabled.

Q17. Explain the function of the PSW register in the 8051 microcontroller.
A17. The PSW (Program Status Word) register in the 8051 microcontroller contains status flags and the stack pointer. It includes flags for carry, auxiliary carry, overflow, parity, and user-defined flags.

Q18. What is the function of the EA (Enable All) pin in the 8051 microcontroller?
A18. The EA (Enable All) pin is used to enable or disable all interrupts in the 8051 microcontroller. When the EA pin is pulled high, interrupts are enabled, and when it is pulled low, interrupts are disabled.

Q19. How does the 8051 microcontroller handle I/O operations?
A19. The 8051 microcontroller has four 8-bit I/O ports (P0, P1, P2, and P3) that can be used for both input and output operations. These ports can be configured as either input or output by setting or clearing the corresponding bits in the Data Direction Register (DDR) for each port.

Q20. Can the 8051 microcontroller operate on a single power supply voltage?
A20. No, the 8051 microcontroller requires a minimum of two power supply voltages - VCC and VSS. VCC supplies the positive power, while VSS is the ground or negative power reference.

These additional questions should provide you with a broader understanding of the 8051 microcontroller. Remember to study the concepts in depth, explore practical examples, and practice coding exercises to enhance your knowledge and skills. Best of luck with your interview.

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