Question 1

Q.1. What does the term Embedded System mean?

Accepted Answer

An embedded system is a dedicated computer system, combining a microprocessor/microcontroller with software, designed to perform one or a few specific, predefined functions within a larger mechanical or electrical system, rather than serving as a general-purpose computer.

Question 2

Q.2. What is the drawback of Memory Mapped I/O?

Accepted Answer

The main drawback of memory-mapped I/O is that it consumes part of the available memory address space for I/O devices, reducing memory available for program/data, and typically requires longer/slower memory-reference instructions instead of dedicated, shorter I/O instructions.

Question 3

Q.3. List the benefits of subroutine.

Accepted Answer

Subroutines offer benefits of code reusability, reduced overall program size, easier debugging and maintenance, and improved program modularity.

Question 4

Q.4. How is the A/D converter interfaced with 8051 microcontroller?

Accepted Answer

An A/D converter (such as ADC0808) is interfaced with the 8051 through its 8-bit digital output bus connected to a data port, and its ALE, START, EOC and OE control signals connected to individual I/O pins that the program toggles in sequence to select a channel, start conversion, detect completion, and read the resulting digital value.

Question 5

Q.5. Give four differences between Static and Dynamic RAM.

Accepted Answer

Static RAM (SRAM) uses flip-flop-based bistable latching cells requiring no periodic refresh but consuming more chip area/power per bit, while Dynamic RAM (DRAM) stores each bit as charge on a tiny capacitor requiring periodic refresh circuitry, but achieves much higher storage density and lower cost per bit, at the expense of somewhat slower access and higher design complexity.

Question 6

Q.6. Why are AD0-AD7 lines multiplexed?

Accepted Answer

AD0-AD7 lines are multiplexed (shared between address and data functions) to reduce the total pin count of the microprocessor package, since dedicating separate pins for the full address bus and full data bus simultaneously would require significantly more physical pins on the IC.

Question 7

Q.7. What are the different types of Addressing modes in 8051?

Accepted Answer

The 8051 supports several addressing modes: immediate, register, direct, register-indirect, indexed (for lookup tables in code memory), and relative (for conditional jumps).

Question 8

Q.8. Differentiate between 16-bit & 32-bit microcontrollers.

Accepted Answer

16-bit microcontrollers process data in 16-bit words with moderate speed and memory capacity, suited to mid-complexity applications, while 32-bit microcontrollers (e.g., ARM Cortex-M) process full 32-bit words with much higher clock speeds, larger memory addressing, and more sophisticated peripherals, suited to complex, high-performance embedded applications.

Question 9

Q.9. Draw the block diagram of 8051 microcontroller and label it properly.

Accepted Answer

The 8051 block diagram comprises the CPU (ALU, register array, PSW), internal ROM/RAM, four I/O ports (P0-P3), two 16-bit timers, a serial port (UART), an interrupt control unit, and an oscillator/clock circuit, all interconnected via an internal bus system.

Question 10

Q.10. Differentiate between Timers and Counters. Draw the diagram of TCON in …

Accepted Answer

A timer counts internal clock (machine cycle) pulses to measure elapsed time, while a counter counts external pulses applied to the T0/T1 pins to count external events; both functions are configured and controlled via the TCON register, which contains the run-control bits (TR0, TR1) and overflow flags (TF0, TF1) for both timers.

Question 11

Q.1. What is the use of Stack? Explain "PUSH" and "POP" operations with the h…

Accepted Answer

A stack is a Last-In-First-Out (LIFO) memory structure used to temporarily save the Program Counter (during CALL/interrupt) and register contents; PUSH copies a register pair's contents onto the stack (decrementing SP), while POP retrieves them back off the stack (incrementing SP), always in reverse order of pushing.

Question 12

Q.2. Briefly describe the key features of Synchronous and Asynchronous commun…

Accepted Answer

Synchronous communication uses a shared clock signal for continuous, high-speed data transfer with no per-character framing overhead, while asynchronous communication transmits data one character at a time with individual start/stop bit framing and no shared clock, trading efficiency for simplicity and tolerance of clock mismatch.

Question 13

Q.3. Elaborate the instructions set in 8051 microcontroller with the help of …

Accepted Answer

The 8051 instruction set includes data transfer (MOV, MOVX, MOVC), arithmetic (ADD, SUBB, INC, DEC, MUL, DIV), logical (ANL, ORL, XRL, CPL), branching (SJMP, LJMP, conditional jumps, CALL/RET), and bit-manipulation (SETB, CLR, CPL, JB, JNB) instruction categories, each illustrated with a representative example.

Question 14

Q.4. Draw the T-states and Machine cycles for the following instructions: (a)…

Accepted Answer

CMP r takes 1 machine cycle (4 T-states, opcode fetch only), STAX takes 2 machine cycles (7 T-states, opcode fetch + memory write), LDA addr takes 4 machine cycles (13 T-states, opcode fetch + 2 address-byte reads + 1 data read), and STA addr takes 4 machine cycles (13 T-states, opcode fetch + 2 address-byte reads + 1 data write).

Question 15

Q.5. Explain various timers and interrupts and their functions in 8051 microc…

Accepted Answer

The 8051 has two 16-bit timers (Timer 0, Timer 1) with four selectable operating modes for timing, event counting, and baud-rate generation, and five interrupt sources (two external, two timer-overflow, one serial port), each individually enabled via IE and prioritized via IP, together enabling precise time-delay generation and responsive real-time event handling.

Question 16

Q.6. Explain the interfacing of Analog to Digital and Digital to Analog conve…

Accepted Answer

An ADC (such as ADC0808) is interfaced via a data port and control lines (ALE, START, EOC, OE) to convert an analog input into digital data readable by the 8051, while a DAC (such as DAC0808) is interfaced via a data port that the 8051 writes a digital value to, which the DAC converts into a corresponding analog output current/voltage.

Question 17

Q.7. Show the interfacing circuit and functional pins of LCD.

Accepted Answer

A 16×2 LCD module is interfaced with the 8051 via an 8-bit (or 4-bit) data bus connected to a port, plus RS (Register Select), R/W (Read/Write) and E (Enable) control lines, with the microcontroller writing command bytes (RS=0) to configure the display and data bytes (RS=1) to display ASCII characters, using an Enable-pulse handshake for each write.

Question 18

Q.1. A binary coded decimal number between 0 and 99 is stored in R/W memory l…

Accepted Answer

The BCD-to-binary conversion subroutine processes each BCD digit weight by weight, computing binary = tens_digit×10 + units_digit using repeated addition/multiplication via shifts and adds, since the 8085 lacks a direct hardware multiply instruction, with the main program calling the BCDBIN subroutine and storing the final binary result in OUTBUF.

Question 19

Q.2. Draw and explain the architecture of 8051 Microcontroller. Give PSW of 8…

Accepted Answer

The 8051 architecture comprises the CPU (ALU, register array, PSW), on-chip ROM and RAM, four I/O ports, two timers, a serial port, and an interrupt system, all connected via internal buses; the 8-bit PSW register holds the CY, AC, F0, RS1/RS0, OV, and P flags, used for arithmetic status and register bank selection.

Question 20

Q.3. With the help of schematic diagram, explain the interfacing of stepper m…

Accepted Answer

A stepper motor is interfaced with the 8051 through a ULN2003 driver IC that amplifies the microcontroller's port outputs to drive the motor's winding currents in a defined excitation sequence; direction is reversed by traversing the step-pattern table in reverse order, and speed is controlled by the delay inserted between successive steps.

Question 21

Q.4. Draw the pin diagram of programmable peripheral interface chip 8255 and …

Accepted Answer

The 8255 Programmable Peripheral Interface is a 40-pin chip providing three 8-bit I/O ports (A, B, C) configurable via its Control Word Register into Mode 0 (simple I/O), Mode 1 (handshake I/O), or Mode 2 (bidirectional handshake I/O, Port A only), enabling flexible parallel I/O expansion for a microprocessor system.

Question 22

Q.5. Write an assembly language program to perform traffic light control oper…

Accepted Answer

A traffic light control assembly program cycles the outputs of a microcontroller port (each bit driving a red/yellow/green lamp for two intersecting roads) through a predefined sequence of lamp-combination states, holding each state for an appropriate time delay (using a timer or software delay subroutine) before advancing to the next state in the cycle.

Microprocessor