Embedded System (4343204) - Summer 2024 Solution

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Question 1(a) [3 marks]

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Draw AVR status register.

Answer:

The AVR Status Register (SREG) contains information about the result of arithmetic operations and controls interrupts.

Diagram:

• I (bit 7): Global Interrupt Enable
• T (bit 6): Bit Copy Storage
• H (bit 5): Half Carry Flag
• S (bit 4): Sign Flag (S = N⊕V)
• V (bit 3): Two’s Complement Overflow
• N (bit 2): Negative Flag
• Z (bit 1): Zero Flag
• C (bit 0): Carry Flag

Mnemonic: “I Take Health Seriously, Very Nice Zero Carry”

Question 1(b) [4 marks]

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Explain Harvard Architecture in the AVR.

Answer:

Harvard Architecture in AVR separates program and data memory, allowing simultaneous access to both.

Diagram:

graph TD
    CPU[CPU]
    PM[Program Memory]
    DM[Data Memory]
    CPU -->|Instruction Bus| PM
    CPU -->|Data Bus| DM

• Program Memory: Stores instructions in Flash memory
• Data Memory: Contains SRAM, registers, and I/O registers
• Separate Buses: Different buses for program and data
• Parallel Access: Can fetch instruction and access data simultaneously

Mnemonic: “Separate Places for Data And Programs”

Question 1(c) [7 marks]

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Discuss real time operating system.

Answer:

Real-Time Operating System (RTOS) manages tasks with strict timing requirements, ensuring predictable response times.

Table: Key Features of RTOS

• Task-based: Divides program into independent tasks
• Interrupt Handling: Fast response to external events
• Synchronization: Provides semaphores and mutexes for task coordination
• Resource Management: Prevents resource conflicts
• Small Footprint: Optimized for limited hardware resources

Mnemonic: “Tasks Run On Strict Timelines”

Question 1(c OR) [7 marks]

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Discuss criteria for choosing microcontroller for embedded system.

Answer:

Selecting the right microcontroller requires evaluating several key factors to match application requirements.

Table: Microcontroller Selection Criteria

• Application Needs: Match controller to task complexity
• Real-time Requirements: Response time constraints
• Environmental Factors: Temperature, noise, vibration
• Form Factor: Physical size and packaging
• Future Expansion: Room for feature growth

Mnemonic: “Power, Memory, I/O, Peripherals, Cost”

Question 2(a) [3 marks]

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Define embedded system and draw its general block diagram.

Answer:

An embedded system is a dedicated computer system designed for specific functions within a larger mechanical or electrical system.

Diagram:

• Processing Unit: Microcontroller/microprocessor
• Memory: Stores program and data
• Input/Output: Interfaces with external world

Mnemonic: “Processing Memory I/O Power”

Question 2(b) [4 marks]

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List I/O registers associated with each port.

Answer:

AVR microcontrollers have three primary registers for controlling each I/O port.

Table: I/O Port Registers

• x represents: A, B, C, D (port letter)
• Additional Special: Some ports have PCMSK (Pin Change Mask) registers

Mnemonic: “Direction, Data, Pin reading”

Question 2(c) [7 marks]

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Explain clock and reset circuit for AVR.

Answer:

The clock and reset circuits ensure proper initialization and timing of AVR operations.

Clock Circuit Diagram:

Reset Circuit:

• Clock Source: External crystal, RC oscillator, or internal oscillator
• Crystal: Provides accurate timing (1-16 MHz)
• Reset Pin: Active-low input for system restart
• Power-on Reset: Automatic reset when power applied
• Brown-out Detection: Reset if voltage drops below threshold

Mnemonic: “Crystal Oscillates, Reset Ensures Start”

Question 2(a OR) [3 marks]

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Write characteristics of embedded system.

Answer:

Embedded systems have unique characteristics that distinguish them from general-purpose computers.

Table: Embedded System Characteristics

• Long Life: Often operates for years without intervention
• Often Hidden: Integrated within larger systems

Mnemonic: “Single, Real-time, Resource-limited, Reliable”

Question 2(b OR) [4 marks]

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Discuss the role of DDRx in outputting and inputting data.

Answer:

DDRx (Data Direction Register) configures each pin of port x as either input or output.

Table: DDRx Role in I/O Operations

• Direction Control: 1 = output, 0 = input
• Pin-specific: Each bit controls individual pin
• Initial State: Default is input (all 0s)

Mnemonic: “Direction Determines Data flow”

Question 2(c OR) [7 marks]

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Draw and explain ATmega32 pin diagram.

Answer:

ATmega32 is a popular 8-bit AVR microcontroller with 40 pins providing various functionalities.

Diagram:

• Port A (PA0-PA7): 8-bit bidirectional port with ADC inputs
• Port B (PB0-PB7): 8-bit port with SPI, timers, and external interrupts
• Port C (PC0-PC7): 8-bit bidirectional port with TWI support
• Port D (PD0-PD7): 8-bit port with USART, external interrupts, and PWM
• Power/Ground: VCC, GND, AVCC, AREF
• Clock: XTAL1/XTAL2 for external oscillator
• Reset: Active-low reset input

Mnemonic: “ABCD Ports Around Power Clock Reset”

Question 3(a) [3 marks]

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Explain Program Counter (PC) register for ATmega32.

Answer:

Program Counter (PC) is a 16-bit register that tracks the address of the next instruction to execute.

Diagram:

• Function: Points to next instruction in program memory
• Size: 16-bit (can address up to 64K words)
• Auto-increment: Automatically increments after instruction fetch
• Jump Control: Modified by branch and jump instructions

Mnemonic: “Points to Code Execution”

Question 3(b) [4 marks]

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Write an AVR C program to read the content of location 0x005F of EEPROM into PORTB.

Answer:

#include <avr/io.h>
#include <avr/eeprom.h>

int main(void)
{
    // Set PORTB as output
    DDRB = 0xFF;
    
    // Read from EEPROM location 0x005F and output to PORTB
    PORTB = eeprom_read_byte((uint8_t*)0x005F);
    
    while(1) {
        // Main loop
    }
    return 0;
}

• DDRB = 0xFF: Configure all PORTB pins as outputs
• eeprom_read_byte(): AVR library function to read EEPROM
• while(1): Infinite loop to maintain output

Mnemonic: “Direction, Read EEPROM, Output to Port”

Question 3(c) [7 marks]

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Draw and explain TCCR0 register in detail.

Answer:

Timer/Counter Control Register 0 (TCCR0) controls the operation of Timer/Counter0.

Diagram:

Table: TCCR0 Bits Function

• WGM01:0: Selects Normal, CTC, or PWM modes
• COM01:0: Defines OC0 pin behavior on compare match
• CS02:0: Sets clock source and prescaler (1, 8, 64, 256, 1024)

Mnemonic: “Forcing Waveforms, Comparing, Selecting Clock”

Question 3(a OR) [3 marks]

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Explain AVR data memory.

Answer:

AVR data memory consists of multiple sections for different types of data storage.

Diagram:

graph TD
    A[AVR Data Memory]
    A --> B[Registers]
    A --> C[I/O Registers]
    A --> D[Internal SRAM]
    A --> E[EEPROM]

• Registers: 32 general-purpose registers (R0-R31)
• I/O Memory: Special function registers for peripherals
• SRAM: Internal RAM for variables (volatile)
• EEPROM: Non-volatile memory for persistent data

Mnemonic: “Registers I/O SRAM EEPROM”

Question 3(b OR) [4 marks]

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Write an AVR C program to store ‘G’ into location 0x005F of EEPROM.

Answer:

#include <avr/io.h>
#include <avr/eeprom.h>

int main(void)
{
    // Store character 'G' to EEPROM location 0x005F
    eeprom_write_byte((uint8_t*)0x005F, 'G');
    
    while(1) {
        // Main loop
    }
    return 0;
}

• eeprom_write_byte(): AVR library function to write to EEPROM
• ‘G’: ASCII value 71 (0x47) stored in EEPROM
• 0x005F: Target EEPROM address
• while(1): Infinite loop after writing

Mnemonic: “Write Once, Remember Forever”

Question 3(c OR) [7 marks]

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Draw and explain TIFR register in detail.

Answer:

Timer/Counter Interrupt Flag Register (TIFR) holds flags that indicate timer events.

Diagram:

Table: TIFR Bits Function

• TOV0: Set when Timer0 overflows, cleared when ISR executes
• TOV2: Set when Timer2 overflows
• OCF2: Set when Timer2 compare match occurs
• Flag Clearing: Write ‘1’ to bit to clear flag

Mnemonic: “Timers Overflow, Comparisons Flag”

Question 4(a) [3 marks]

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Write different ways of generating delay in AVR.

Answer:

AVR microcontrollers offer multiple methods to generate time delays.

Table: Delay Generation Methods

• Software: Simple but affected by optimizations
• Hardware: More accurate but requires timer setup
• Library: Convenient but limited to constant values

Mnemonic: “Loops, Interrupts, Polling, Functions”

Question 4(b) [4 marks]

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Draw and explain interfacing of LM35 with ATmega32.

Answer:

LM35 is a temperature sensor that outputs an analog voltage proportional to temperature.

Circuit Diagram:

• Connection: LM35 output to ADC0 (PA0) of ATmega32
• Scaling: 10mV/°C output (0°C = 0V, 25°C = 250mV)
• ADC Setup: Configure ADMUX to select ADC0
• Calculation: Temperature = (ADC_value * 5 * 100) / 1024

Mnemonic: “Analog Voltage Converts Temperature”

Question 4(c) [7 marks]

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Explain interfacing of MAX7221 with ATmega32 in detail.

Answer:

MAX7221 is an LED display driver IC that connects to AVR using SPI communication.

Circuit Diagram:

Table: Connections and Functionality

• SPI Mode: Master mode, MSB first
• Initialization: Set decode mode, intensity, scan limit
• Data Transfer: Send address byte followed by data byte
• Multiplexing: Can drive up to 8 digits
• Brightness Control: 16 levels through intensity register

Mnemonic: “Send Clock Data Load Display”

Question 4(a OR) [3 marks]

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Explain MAX232 line driver.

Answer:

MAX232 is an IC that converts TTL/CMOS logic levels to RS-232 voltage levels for serial communication.

Diagram:

• Voltage Conversion: TTL (0/5V) to RS-232 (±12V)
• Charge Pumps: Uses capacitors to generate required voltages
• Applications: Serial communication with PC, modems
• Bidirectional: Handles both transmit and receive signals

Mnemonic: “TTL To RS-232 Conversion”

Question 4(b OR) [4 marks]

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Explain ADMUX register.

Answer:

ADC Multiplexer Selection Register (ADMUX) controls analog input channel selection and result format.

Diagram:

Table: ADMUX Bit Functions

• REFS1:0: Select voltage reference (AREF, AVCC, Internal)
• ADLAR: Result alignment in ADC registers
• MUX3:0: Select input channel (ADC0-ADC7)

Mnemonic: “Reference, Alignment, Multiplexer”

Question 4(c OR) [7 marks]

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Discuss Two Wire serial Interface (TWI) in AVR.

Answer:

Two Wire Interface (TWI) is AVR’s implementation of I²C protocol for communication with peripheral devices.

Diagram:

graph LR
    A[Master AVR] -- SDA --- B[Slave 1]
    A -- SCL --- B
    B -- SDA --- C[Slave 2]
    B -- SCL --- C

Table: TWI Characteristics

• Bidirectional: Both devices can transmit and receive
• Registers: TWBR, TWCR, TWSR, TWDR, TWAR
• ACK/NACK: Acknowledgment for reliable transfers
• Start/Stop: Special conditions to begin/end transmission
• Common Uses: EEPROM, RTC, sensors, displays

Mnemonic: “Serial Clock And Data Transfers”

Question 5(a) [3 marks]

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Draw circuit diagram to interface DC motor with ATmega32 using L293D motor driver.

Answer:

L293D provides bidirectional drive current for controlling DC motors with microcontrollers.

Circuit Diagram:

• Control Pins: PD0, PD1 control motor direction
• Driver Power: Separate for logic and motor
• H-Bridge: Enables forward/reverse operation
• Enable Pin: Can be used for PWM speed control

Mnemonic: “Direction Control Through Bridge”

Question 5(b) [4 marks]

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Write features of on chip ADC in ATmega32.

Answer:

ATmega32 features a versatile analog-to-digital converter for measuring analog signals.

Table: ATmega32 ADC Features

• Successive Approximation: Conversion technique
• Multiplexer: Selects among 8 input channels
• Interrupt: Optional interrupt on completion
• Sampling Rate: Up to 15 KSPS at maximum resolution

Mnemonic: “Multiple Channels, Ten-bit Resolution”

Question 5(c) [7 marks]

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Explain Smart Irrigation System.

Answer:

Smart Irrigation System automates watering based on environmental conditions using microcontroller technology.

Diagram:

graph TD
    A[ATmega32] --> B[Soil Moisture Sensor]
    A --> C[Temperature Sensor]
    A --> D[Humidity Sensor]
    A --> E[Water Pump Control]
    A --> F[Valve Control]
    A --> G[LCD Display]
    H[RTC Module] --> A

Table: System Components

• Adaptive Control: Adjusts watering based on conditions
• Water Conservation: Uses only necessary amount of water
• Remote Monitoring: Optional WiFi/GSM connectivity
• Data Logging: Records moisture levels and watering events
• Battery Backup: Ensures operation during power outages

Mnemonic: “Sense Moisture, Control Water Automatically”

Question 5(a OR) [3 marks]

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Draw and explain pin diagram of L293D motor driver IC.

Answer:

L293D is a quadruple half-H driver IC used for controlling motors and other inductive loads.

Diagram:

• VCC1 (Pin 16): Logic supply voltage (5V)
• VCC2 (Pin 8): Motor supply voltage (4.5V-36V)
• EN1/EN2: Enable inputs (can be PWM for speed control)
• IN1-IN4: Logic inputs to control direction
• OUT1-OUT4: Outputs to connect motors
• GND: Ground connections

Mnemonic: “Enable, Input, Output, Power”

Question 5(b OR) [4 marks]

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List registers associated with ADC in AVR.

Answer:

AVR’s ADC system uses several registers to control its operation and store results.

Table: ADC Registers

• ADMUX: Channel and reference selection
• ADCSRA: Enable ADC, start conversion, prescaler
• ADCH/ADCL: Result registers (10-bit value)
• SFIOR: Auto-trigger sources (Timer, External)

Mnemonic: “Multiplexer Controls And Delivers Results”

Question 5(c OR) [7 marks]

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Explain IoT based home automation system.

Answer:

IoT home automation connects household devices to the internet for remote monitoring and control.

Diagram:

graph TD
    A[Internet] --- B[WiFi Gateway]
    B --- C[AVR Controller]
    C --- D[Light Control]
    C --- E[Fan Control]
    C --- F[Door Lock]
    C --- G[Temperature Sensors]
    C --- H[Motion Sensors]
    B --- I[Mobile App]
    B --- J[Cloud Services]

Table: System Components

• Remote Access: Control home from anywhere
• Scheduling: Automate device operation based on time
• Voice Control: Integration with digital assistants
• Energy Monitoring: Track power consumption
• Security: Alerts for unusual activities
• Scene Setting: One-touch control of multiple devices

Mnemonic: “Connect, Control, Automate, Monitor”