Microprocessor and Microcontroller (4341101) - Summer 2023 Solution

Question 1(a) [3 marks]

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Compare Microprocessor and Microcontroller.

Answer:

Mnemonic: “PCRAM” - “Processors Connect to RAM, Microcontrollers Already have Memory”

Question 1(b) [4 marks]

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Compare RISC and CISC.

Answer:

Mnemonic: “RISC-Fast, CISC-Many” (RISC uses Fast execution, CISC has Many instructions)

Question 1(c) [7 marks]

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Define: Microprocessor, Operand, Instruction Cycle, Opcode, ALU, Machine Cycle, T-State

Answer:

Diagram:

Mnemonic: “My Old Intel Chip Only Makes Trouble” (Microprocessor, Operand, Instruction, Opcode, ALU, Machine, T-state)

Question 1(c OR) [7 marks]

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Compare Von-Neumann and Harvard architecture.

Answer:

Diagram:

Mnemonic: “Harvard Has Separate Streets” (Harvard Has Separate memory paths)

Question 2(a) [3 marks]

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Draw Flag Register of 8085 microprocessor & explain it.

Answer:

Diagram:

Mnemonic: “Smart Zombies Always Prefer Candy” (Sign, Zero, Auxiliary, Parity, Carry)

Question 2(b) [4 marks]

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Explain De-multiplexing of Address and Data buses for 8085 Microprocessor.

Answer:

Diagram:

• Need: 8085 has multiplexed pins (AD0-AD7) to save pins
• Process:
  1. CPU places address on AD0-AD7 pins
  2. ALE (Address Latch Enable) signal goes HIGH
  3. Address latch (74LS373) captures lower address bits
  4. ALE goes LOW, latching the address
  5. AD0-AD7 pins now free for data transfer

Mnemonic: “ALE Latches, Data Follows” (Address Latch Enable captures address first, then data)

Question 2(c) [7 marks]

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Describe architecture of 8085 microprocessor with the help of neat diagram.

Answer:

Diagram:

• Main Components:

  • Registers: Storage locations (A, B-L, SP, PC, Flags)
  • ALU: Performs arithmetic and logical operations
  • Control Unit: Generates timing and control signals
  • Buses: Address bus (16-bit), Data bus (8-bit), Control bus

• Key Features:

  • 8-bit data bus, 16-bit address bus (64KB addressable memory)
  • 6 general-purpose registers (B,C,D,E,H,L) and accumulator
  • 5 flags for status information

Mnemonic: “RABC” - “Registers, ALU, Buses, Control” (main components)

Question 2(a OR) [3 marks]

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Explain Bus Organization of 8085 microprocessor.

Answer:

Key Control Signals:

• RD̅: Read signal (active low)
• WR̅: Write signal (active low)
• ALE: Address Latch Enable
• IO/M̅: Distinguishes I/O (high) from memory (low) operations

Diagram:

Mnemonic: “ADC” - “Address finds, Data travels, Control coordinates”

Question 2(b OR) [4 marks]

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Explain: Program Counter & Stack pointer

Answer:

Program Counter (PC):

• Automatically increments after instruction fetch
• Modified by jump/call instructions
• Controls program execution sequence
• Initially set to 0000H on reset

Stack Pointer (SP):

• Points to last data item pushed onto stack
• Stack works in LIFO (Last In First Out) manner
• Used during subroutine calls and interrupts
• Stack grows downward in memory (decrements)

Diagram:

Mnemonic: “PC Previews, SP Stacks” (PC points to next instruction, SP manages stack)

Question 2(c OR) [7 marks]

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Describe Pin diagram of 8085 microprocessor with the help of neat diagram.

Answer:

Diagram:

Pin Groups:

1. Power & Clock: Vcc, GND, X1, X2, CLK
2. Address/Data: A8-A15, AD0-AD7 (multiplexed)
3. Control: ALE, RD̅, WR̅, IO/M̅
4. Interrupt: INTR, INTA, RST 5.5/6.5/7.5, TRAP
5. DMA: HOLD, HLDA
6. Serial I/O: SID, SOD
7. Status: S0, S1

Mnemonic: “PACI-DHS” (Power, Address, Control, Interrupt, DMA, Hardware status, Serial)

Question 3(a) [3 marks]

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Explain Stack, Stack Pointer and Stack operation.

Answer:

Diagram:

Mnemonic: “LIFO Saves Push-Pop” (Last-In-First-Out with Push and Pop operations)

Question 3(b) [4 marks]

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Draw Timers/Counters logic diagram of 8051 microcontroller and explain it.

Answer:

Diagram:

• 8051 has 2 16-bit timers/counters: Timer 0 and Timer 1
• Each timer has two 8-bit registers: THx (High byte) and TLx (Low byte)
• 4 Operating Modes:
  • Mode 0: 13-bit timer
  • Mode 1: 16-bit timer
  • Mode 2: 8-bit auto-reload
  • Mode 3: Split timer mode
• Two Functions:
  • Timer: Counts internal clock pulses
  • Counter: Counts external events

Mnemonic: “TIME-C” (Timer Input, Mode select, External count)

Question 3(c) [7 marks]

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With the help of neat diagram explain Pin diagram of 8051 microcontroller.

Answer:

Diagram:

Pin Groups:

1. Port Pins:
   • P0 (Port 0): 8-bit bidirectional, multiplexed address/data
   • P1 (Port 1): 8-bit bidirectional I/O
   • P2 (Port 2): 8-bit bidirectional, higher address byte
   • P3 (Port 3): 8-bit bidirectional with alternate functions
2. Power & Clock: VCC, GND, XTAL1, XTAL2
3. Control Signals:
   • RST: Reset input
   • ALE: Address Latch Enable
   • PSEN: Program Store Enable
   • EA: External Access

Mnemonic: “PORT-CAPS” (Ports 0-3, Clock, Address latch, Program store, Supply)

Question 3(a OR) [3 marks]

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Explain Serial communication modes of 8051 microcontroller.

Answer:

Key Components:

• SBUF: Serial buffer register
• SCON: Serial control register
• P3.0 (RXD): Receive pin
• P3.1 (TXD): Transmit pin

Diagram:

Mnemonic: “SMART” (Serial Modes Are Rate and Timing dependent)

Question 3(b OR) [4 marks]

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Explain Internal RAM Organization of 8051 microcontroller.

Answer:

Diagram:

Key Features:

• Only one register bank active at a time (selected by PSW bits)
• Each bit in bit-addressable area has its own address (20H.0-2FH.7)
• Stack can be located anywhere in internal RAM

Mnemonic: “RGB-S” (Registers, General purpose, Bit-addressable, SFRs)

Question 3(c OR) [7 marks]

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Explain architecture of 8051 microcontroller with the help of neat diagram.

Answer:

Diagram:

Key Components:

• CPU: 8-bit processor with ALU, registers, and control logic
• Memory:
  • 4KB internal ROM (program memory)
  • 128 bytes internal RAM (data memory)
• I/O: Four 8-bit I/O ports (P0-P3)
• Timers: Two 16-bit timers/counters
• Serial Port: Full-duplex UART
• Interrupts: Five interrupt sources with two priority levels

Mnemonic: “BASICS” (Bus, Architecture with CPU, Serial port, I/O ports, Counters/timers, Special functions)

Question 4(a) [3 marks]

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Write an 8051 Assembly Language Program to Exchange lower nibbles of register R5 and R6: put the lower nibble of R5 into R6, and the lower nibble of R6 into R5.

Answer:

      ; Exchange lower nibbles of R5 and R6
      MOV A, R5    ; Copy R5 to accumulator
      ANL A, #0FH  ; Mask upper nibble (keep only lower nibble)
      MOV B, A     ; Save R5's lower nibble in B
      
      MOV A, R6    ; Copy R6 to accumulator
      ANL A, #0FH  ; Mask upper nibble (keep only lower nibble)
      MOV C, A     ; Save temporarily in a free register (R7)
      
      MOV A, R5    ; Get R5 again
      ANL A, #F0H  ; Keep only upper nibble of R5
      ORL A, C     ; Combine with lower nibble from R6
      MOV R5, A    ; Store result back in R5
      
      MOV A, R6    ; Get R6 again
      ANL A, #F0H  ; Keep only upper nibble of R6
      ORL A, B     ; Combine with lower nibble from R5
      MOV R6, A    ; Store result back in R6

Diagram:

Mnemonic: “MAMS” (Mask, And, Move, Swap)

Question 4(b) [4 marks]

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Write an 8051 Assembly Language Program to blink LED interfaced at port P1.0 at time interval of 1ms.

Answer:

      ORG 0000H        ; Start at memory location 0000H
MAIN: CPL P1.0         ; Complement P1.0 (toggle LED)
      ACALL DELAY      ; Call delay subroutine
      SJMP MAIN        ; Loop forever

DELAY: MOV R7, #2      ; Load R7 for outer loop (2)
DELAY1: MOV R6, #250   ; Load R6 for inner loop (250)
DELAY2: NOP            ; No operation (consume time)
        NOP            ; Additional delay
        DJNZ R6, DELAY2 ; Decrement R6 & loop until zero
        DJNZ R7, DELAY1 ; Decrement R7 & loop until zero
        RET            ; Return from subroutine

Diagram:

Mnemonic: “TCDL” (Toggle, Call, Delay, Loop)

Question 4(c) [7 marks]

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List Addressing Modes of 8051 Microcontroller and explain them with at least one example.

Answer:

Diagram:

Mnemonic: “RIDDIBM” (Register, Immediate, Direct, Data, Indirect, Bit, iMplied)

Question 4(a OR) [3 marks]

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Write an 8051 Assembly Language Program to add the byte in register R2 and R3, put the result in external RAM 2040h (LSB) and 2041h (MSB).

Answer:

      MOV A, R2      ; Move R2 to accumulator
      ADD A, R3      ; Add R3 to accumulator
      MOV DPTR, #2040H ; Set DPTR to external RAM address 2040H
      MOVX @DPTR, A  ; Store the result (LSB) at 2040H
      
      MOV A, #00H    ; Clear accumulator
      ADDC A, #00H   ; Add carry flag to accumulator
      INC DPTR       ; Increment DPTR to 2041H
      MOVX @DPTR, A  ; Store the result (MSB) at 2041H

Diagram:

Mnemonic: “MASIM” (Move, Add, Store, Increment, Move again)

Question 4(b OR) [4 marks]

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For 8051 Microcontroller with a crystal frequency of 12 MHz, generate a delay of 5ms.

Answer:

      ; Delay of 5ms with 12MHz Crystal (1 machine cycle = 1μs)
DELAY: MOV R7, #5     ; 5 loops of 1ms each
LOOP1: MOV R6, #250   ; 250 x 4μs = 1000μs = 1ms
LOOP2: NOP            ; 1μs
       NOP            ; 1μs
       DJNZ R6, LOOP2 ; 2μs (if jump taken)
       DJNZ R7, LOOP1 ; Repeat 5 times for 5ms
       RET            ; Return from subroutine

Diagram:

Calculation:

• 12MHz crystal = 1μs machine cycle
• Inner loop: 2 NOPs (2μs) + DJNZ (2μs) = 4μs per iteration
• 250 iterations × 4μs = 1000μs = 1ms
• Outer loop: 5 iterations × 1ms = 5ms

Mnemonic: “LOON-5” (LOOp Nested for 5ms)

Question 4(c OR) [7 marks]

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Explain any seven Arithmetic Instructions with example for 8051 Microcontroller.

Answer:

Diagram:

Mnemonic: “ACID-IBM” (Add, Carry add, Inc, Dec, Mul, Borrow subtract, Divide)

Question 5(a) [3 marks]

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List Applications of microcontroller in various fields.

Answer:

Diagram:

Mnemonic: “CHAIM-MA” (Consumer, Home, Automotive, Industrial, Medical, Mobile, Aerospace)

Question 5(b) [4 marks]

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Interface Relay with 8051 microcontroller.

Answer:

Diagram:

Components Required:

• 8051 microcontroller
• ULN2003 or similar driver IC
• Relay (5V or 12V)
• Protection diode (1N4007)
• Power supply

Working:

1. 8051 sends control signal from P1.0
2. Driver amplifies current to drive relay
3. Protection diode prevents back EMF damage
4. Relay switches connected devices

Mnemonic: “DRIPS” (Driver, Relay, Input from µC, Protection diode, Switching)

Question 5(c) [7 marks]

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Interface LCD with 8051 microcontroller.

Answer:

Diagram:

Connections:

• Control Lines:
  • P1.0 → RS (Register Select)
  • P1.1 → R/W (Read/Write)
  • P1.2 → E (Enable)
• Data Lines:
  • P2.0-P2.7 → D0-D7 (8-bit data bus)

Code to Initialize LCD:

MOV A, #38H      ; 2 lines, 5x7 matrix
ACALL COMMAND    ; Send command

MOV A, #0EH      ; Display ON, cursor ON
ACALL COMMAND    ; Send command

MOV A, #01H      ; Clear LCD
ACALL COMMAND    ; Send command

MOV A, #06H      ; Increment cursor
ACALL COMMAND    ; Send command

Mnemonic: “CIDER-8” (Control lines, Initialize, Data bus, Enable, Register select, 8-bit mode)

Question 5(a OR) [3 marks]

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Draw Interfacing of LED with 8051 microcontroller.

Answer:

Diagram:

Components:

• 8051 microcontroller
• LED
• Current limiting resistor (220Ω)
• Power supply

Working Principle:

• Active-Low configuration: LED ON when pin = 0
• P1.0 drives LED through current limiting resistor
• Maximum current should not exceed 20mA per pin

Code for LED Blinking:

MAIN: CLR P1.0    ; Turn ON LED (active low)
      CALL DELAY  ; Wait
      SETB P1.0   ; Turn OFF LED
      CALL DELAY  ; Wait
      SJMP MAIN   ; Repeat

Mnemonic: “CIRCLE” (Current limiting Resistor, IO pin, Cathode to LED, LED to Earth/ground)

Question 5(b OR) [4 marks]

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Interface DC Motor with 8051 microcontroller.

Answer:

Diagram:

Components:

• 8051 microcontroller
• L293D motor driver IC
• DC motor
• Power supply

Control Logic:

Code for Motor Control:

MOV P1, #02H  ; P1.0=0, P1.1=1 (Clockwise)
CALL DELAY    ; Run for some time
MOV P1, #01H  ; P1.0=1, P1.1=0 (Counter-clockwise)
CALL DELAY    ; Run for some time
MOV P1, #00H  ; P1.0=0, P1.1=0 (Stop)

Mnemonic: “DICER” (Driver chip, Input from µC, Control logic, Enable motor, Rotation)

Question 5(c OR) [7 marks]

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Interface DAC0808 with 8051 microcontroller.

Answer:

Diagram:

Components:

• 8051 microcontroller
• DAC0808 (8-bit digital-to-analog converter)
• Operational amplifier (for output buffering)
• RC filter (for smoothing)
• Reference voltage source

Connections:

• P1.0-P1.7 → D0-D7 (8-bit digital input)
• P3.0 → CS (Chip Select)
• DAC output → filter → final analog output

Sample Code for Ramp Signal Generation:

START: MOV R0, #00H      ; Start from 0
LOOP:  MOV P1, R0        ; Output value to DAC
       CALL DELAY        ; Wait
       INC R0            ; Increment value
       SJMP LOOP         ; Loop to create ramp

Applications:

• Waveform generation
• Programmable voltage source
• Motor speed control
• Audio applications

Mnemonic: “DACR” (Digital input, Analog output, Conversion, Reference voltage)