Microprocessor and Microcontroller (4341101) - Summer 2025 Solution

Question 1(a) [3 marks]

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Define Microprocessor and draw its block diagram.

Answer: A microprocessor is a programmable digital device that performs arithmetic and logical operations on data according to stored instructions.

Block Diagram:

graph TD
    A[Input Device] --> B[CPU]
    B --> C[Output Device]
    B <--> D[Memory Unit]
    B --> E[Control Unit]
    B --> F[ALU]
    E --> G[Control Signals]
    F --> H[Arithmetic & Logic Operations]

• CPU: Central Processing Unit performs all operations
• Memory: Stores programs and data
• Control Unit: Controls instruction execution sequence

Mnemonic: “My Computer Processes Instructions” (Memory-CPU-Program-Instructions)

Question 1(b) [4 marks]

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Explain operand and opcode with proper instruction example.

Answer: Opcode specifies the operation to be performed. Operand specifies the data on which operation is performed.

Example Table:

• Opcode: Operation code (MOV, ADD, SUB)
• Operand: Data or address (A, B, #05H)
• Format: Opcode + Operand = Complete Instruction

Mnemonic: “Operation On Data” (Opcode-Operand-Data)

Question 1(c) [7 marks]

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Compare Microprocessor and Microcontroller.

Answer:

• Microprocessor: General purpose computing
• Microcontroller: Specific embedded applications
• Integration: Microcontroller has everything on single chip

Mnemonic: “Micro Means More Integration” (Microcontroller-Memory-More-Integration)

Question 1(c OR) [7 marks]

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Compare RISC and CISC.

Answer:

• RISC: Reduced Instruction Set Computer
• CISC: Complex Instruction Set Computer
• Performance: RISC faster, CISC more flexible

Mnemonic: “Reduced Instructions Speed Computing” (RISC-Instructions-Speed-Computing)

Question 2(a) [3 marks]

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Explain Bus Organization of 8085 microprocessor.

Answer: 8085 has three types of buses for communication with external devices.

Bus Organization Table:

• Address Bus: Unidirectional, 64KB memory addressing
• Data Bus: Bidirectional, 8-bit data transfer
• Control Bus: Read, Write, IO/M signals

Mnemonic: “Address Data Control” (ADC)

Question 2(b) [4 marks]

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Explain function of ALE signal with diagram.

Answer: ALE (Address Latch Enable) separates address and data on multiplexed bus.

ALE Timing Diagram:

• High ALE: Address is available on AD0-AD7
• Low ALE: Data is available on AD0-AD7
• Function: Latches lower address byte
• Frequency: ALE = Clock frequency ÷ 2

Mnemonic: “Address Latch Enable” (ALE)

Question 2(c) [7 marks]

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

Answer:

graph TD
    A[Accumulator A] --> B[ALU]
    C[Temp Register] --> B
    B --> D[Flag Register]
    E[B,C,D,E,H,L Registers] --> F[Address Buffer]
    G[Program Counter] --> F
    H[Stack Pointer] --> F
    F --> I[Address Bus A0-A15]
    J[Data/Address Buffer] --> K[Data Bus AD0-AD7]
    L[Instruction Register] --> M[Instruction Decoder]
    M --> N[Control Unit]
    N --> O[Control Signals]

Key Components:

• ALU: Performs arithmetic and logical operations
• Registers: Store temporary data (A, B, C, D, E, H, L)
• Program Counter: Points to next instruction
• Stack Pointer: Points to stack top
• Control Unit: Generates control signals

Mnemonic: “All Registers Program Stack Control” (A-R-P-S-C)

Question 2(a OR) [3 marks]

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Draw Flag Register of 8085 microprocessor & explain it.

Answer:

Flag Register Format:

Flag Functions:

• S (Sign): Set if result is negative
• Z (Zero): Set if result is zero
• AC (Auxiliary Carry): Set for BCD operations
• P (Parity): Set for even parity
• C (Carry): Set when carry/borrow occurs

Mnemonic: “Some Zero Auxiliary Parity Carry” (SZAPC)

Question 2(b OR) [4 marks]

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

Answer: De-multiplexing separates address and data signals from AD0-AD7 lines.

De-multiplexing Circuit:

• ALE High: Address latched in external latch
• ALE Low: Data flows through buffer
• 74LS373: Common latch IC used
• Benefit: Separate address and data buses

Mnemonic: “Address Latch External Demultiplex” (ALED)

Question 2(c OR) [7 marks]

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

Answer:

Pin Categories:

• Power: VCC, VSS
• Clock: X1, X2, CLK
• Address/Data: AD0-AD7, A8-A15
• Control: ALE, RD, WR, IO/M
• Interrupt: INTR, INTA, RST7.5, RST6.5, RST5.5, TRAP

Mnemonic: “Power Clock Address Control Interrupt” (PCACI)

Question 3(a) [3 marks]

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Write a function of DPTR and PC.

Answer:

Functions Table:

DPTR Functions:

• External Memory: Access external data memory
• Addressing: 16-bit address for MOVX instructions

PC Functions:

• Instruction Pointer: Points to next instruction
• Auto Increment: Increments after each instruction fetch

Mnemonic: “Data Program Counter” (DPC)

Question 3(b) [4 marks]

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Draw PCON SFR of 8051and Explain function of each bit.

Answer:

PCON Register (87H):

Bit Functions:

• SMOD: Serial port baud rate doubler
• GF1, GF0: General purpose flags
• PD: Power Down mode control
• IDL: Idle mode control

Power Management:

• IDL = 1: CPU stops, peripherals run
• PD = 1: Complete power down

Mnemonic: “Serial General Power Idle” (SGPI)

Question 3(c) [7 marks]

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

Answer:

graph TD
    A[CPU Core] --> B[ALU]
    A --> C[Accumulator A]
    A --> D[B Register]
    A --> E[PSW]
    F[Program Memory ROM] --> G[Program Counter PC]
    H[Data Memory RAM] --> I[Data Pointer DPTR]
    J[Timer 0] --> K[Timer Control]
    L[Timer 1] --> K
    M[Serial Port] --> N[Serial Control]
    O[Port 0] --> P[I/O Control]
    Q[Port 1] --> P
    R[Port 2] --> P
    S[Port 3] --> P
    T[Interrupt System] --> U[Interrupt Control]

Major Blocks:

• CPU: 8-bit processor with ALU
• Memory: 4KB ROM, 128B RAM
• Timers: Two 16-bit timers
• Serial Port: Full duplex UART
• I/O Ports: Four 8-bit ports
• Interrupts: 5 interrupt sources

Mnemonic: “CPU Memory Timer Serial IO Interrupt” (CMTSII)

Question 3(a OR) [3 marks]

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List common features of 8051 microcontroller.

Answer:

Common Features:

• CPU: 8-bit microcontroller
• Memory: 4KB ROM, 128B RAM
• I/O Ports: 32 I/O lines (4 ports)
• Timers: Two 16-bit timers/counters
• Serial Port: Full duplex UART
• Interrupts: 5 interrupt sources
• Clock: 12MHz maximum frequency

Mnemonic: “CPU Memory IO Timer Serial Interrupt Clock” (CMITSIC)

Question 3(b OR) [4 marks]

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Draw IP SFR of 8051 and Explain function of each bit.

Answer:

IP Register (B8H):

Bit Functions:

• PS: Serial port interrupt priority
• PT1: Timer 1 interrupt priority
• PX1: External interrupt 1 priority
• PT0: Timer 0 interrupt priority
• PX0: External interrupt 0 priority

Priority Levels:

• 1: High priority
• 0: Low priority

Mnemonic: “Priority Serial Timer External” (PSTE)

Question 3(c OR) [7 marks]

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

Answer:

Pin Groups:

• Power: VCC (40), VSS (20)
• Clock: XTAL1 (19), XTAL2 (18)
• Reset: RST (9)
• Ports: P0, P1, P2, P3
• Control: ALE, PSEN, EA

Mnemonic: “Power Clock Reset Ports Control” (PCRPC)

Question 4(a) [3 marks]

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Explain arithmetic instructions with example.

Answer:

Arithmetic Instructions:

• ADD A,#10H: Add 10H to accumulator
• Flags: Affected by arithmetic operations

Mnemonic: “Add Subtract Multiply Divide Increment Decrement” (ASMIDI)

Question 4(b) [4 marks]

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Write an 8051 Assembly Language Program to Find 2’s complement of a value stored at memory location 65H. Put the result on same location.

Answer:

ORG 0000H           ; Program start address
MOV A,65H           ; Load value from location 65H
CPL A               ; Complement the value (1's complement)
ADD A,#01H          ; Add 1 to get 2's complement
MOV 65H,A           ; Store result back to 65H
SJMP $              ; Stop program
END

Program Steps:

• Load: Get value from memory location 65H
• Complement: Generate 1’s complement using CPL
• Add 1: Convert to 2’s complement
• Store: Put result back to same location

Mnemonic: “Load Complement Add Store” (LCAS)

Question 4(c) [7 marks]

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

Answer:

Addressing Modes Table:

Examples:

• MOV A,#25H: Load immediate value 25H
• MOV A,@R0: Load from address in R0
• SJMP LOOP: Jump relative to current PC

Mnemonic: “Immediate Register Direct Indirect Indexed Relative Bit” (IRDIIRB)

Question 4(a OR) [3 marks]

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Explain logical instruction with example.

Answer:

Logical Instructions:

• ANL A,#0FH: AND accumulator with 0FH (mask operation)
• Applications: Bit masking, data manipulation

Mnemonic: “AND OR XOR Complement Rotate” (AOXCR)

Question 4(b OR) [4 marks]

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Write an 8051 Assembly Language Program to Multiply the number in register R3 by the number in register R0 and put the result in internal RAM location 10h(MSB) and 11h(LSB).

Answer:

ORG 0000H           ; Program start address
MOV A,R3            ; Move R3 to accumulator
MOV B,R0            ; Move R0 to B register
MUL AB              ; Multiply A and B
MOV 10H,B           ; Store MSB (B) to location 10H
MOV 11H,A           ; Store LSB (A) to location 11H  
SJMP $              ; Stop program
END

Program Flow:

• Load: Move multiplicand and multiplier to A and B
• Multiply: Use MUL AB instruction
• Store: MSB in B register, LSB in A register
• Result: 16-bit result stored in two locations

Mnemonic: “Load Multiply Store Result” (LMSR)

Question 4(c OR) [7 marks]

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Explain data transfer instruction with example.

Answer:

Data Transfer Instructions:

Examples:

• MOV A,R0: Move R0 content to accumulator
• MOVX A,@DPTR: Read from external data memory
• PUSH ACC: Push accumulator to stack

Data Movement:

• Internal: Within 8051 memory space
• External: To/from external memory
• Code: From program memory

Mnemonic: “Move Data Between Locations” (MDBL)

Question 5(a) [3 marks]

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Explain the 8051 flags with the help of PSW format.

Answer:

PSW Register (D0H):

Flag Functions:

• C (Carry): Set when carry/borrow occurs
• AC (Auxiliary Carry): For BCD arithmetic
• OV (Overflow): Set when signed overflow
• P (Parity): Even parity of accumulator
• RS1, RS0: Register bank select bits

Mnemonic: “Carry Auxiliary Overflow Parity Register” (CAOPR)

Question 5(b) [4 marks]

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Draw and explain diagram Interfacing 7 segment with microcontroller.

Answer:

7-Segment Interface Circuit:

Components:

• ULN2003: Current driver IC
• Resistors: Current limiting (330Ω)
• Display: Common cathode type

Working: Port data drives display segments through current driver

Mnemonic: “Port Driver Display Ground” (PDDG)

Question 5(c) [7 marks]

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Interface 8 LEDs with microcontroller and write a program to turn on and off.

Answer:

LED Interface Circuit:

Assembly Program:

ORG 0000H           ; Start address
MAIN:
    MOV P1,#0FFH    ; Turn on all LEDs (logic 0)
    CALL DELAY      ; Call delay subroutine
    MOV P1,#00H     ; Turn off all LEDs (logic 1)
    CALL DELAY      ; Call delay subroutine
    SJMP MAIN       ; Repeat continuously

DELAY:
    MOV R2,#250     ; Outer loop counter
D1: MOV R3,#250     ; Inner loop counter  
D2: DJNZ R3,D2      ; Decrement R3 until zero
    DJNZ R2,D1      ; Decrement R2 until zero
    RET             ; Return from subroutine
END

Mnemonic: “Light Emitting Display Interface” (LEDI)

Question 5(a OR) [3 marks]

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List Applications of microcontroller in various fields.

Answer:

Applications by Field:

Mnemonic: “Home Auto Industrial Medical Communication Security Entertainment” (HAIMCSE)

Question 5(b OR) [4 marks]

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Draw and explain diagram interfacing of DC motor with 8051.

Answer:

DC Motor Interface:

Components:

• L293D: Dual H-bridge driver IC
• Motor: 12V DC motor
• Control: Direction and speed control

Control Logic:

• Forward: P1.1=1, P1.2=0
• Reverse: P1.1=0, P1.2=1
• Stop: P1.1=0, P1.2=0

Mnemonic: “Driver Control Motor Direction” (DCMD)

Question 5(c OR) [7 marks]

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Interface LCD with microcontroller and write a program to display “Microprocessor and Microcontroller”.

Answer:

LCD Interface:

Assembly Program:

ORG 0000H
    CALL LCD_INIT       ; Initialize LCD
    MOV DPTR,#MSG1      ; Point to message
    CALL DISPLAY_MSG    ; Display message
    SJMP $              ; Stop

LCD_INIT:
    MOV P1,#38H         ; Function set: 8-bit, 2-line
    CLR P2.0            ; RS=0 (command)
    SETB P2.1           ; EN=1
    CLR P2.1            ; EN=0 (pulse)
    CALL DELAY
    MOV P1,#01H         ; Clear display
    CLR P2.0
    SETB P2.1
    CLR P2.1
    CALL DELAY
    RET

DISPLAY_MSG:
    MOV P1,A            ; Send character
    SETB P2.0           ; RS=1 (data)
    SETB P2.1           ; EN=1
    CLR P2.1            ; EN=0
    CALL DELAY
    RET

MSG1: DB "Microprocessor and Microcontroller",0

DELAY:
    MOV R1,#50
D1: MOV R2,#255
D2: DJNZ R2,D2
    DJNZ R1,D1
    RET
END

Mnemonic: “Liquid Crystal Display Interface” (LCDI)