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Microcontrollers SEM 2 UNIT 5

 Unit 5: 8051 Interrupts and Interfacing Applications



1. Explain the concept of interrupts in the 8051 microcontroller.

(6 Marks)

  • Interrupts are events that temporarily halt the main program execution in the 8051.
  • They allow external devices or internal events to signal the microcontroller for attention.
  • The microcontroller then pauses the current task, saves its state, and executes an Interrupt Service Routine (ISR) specific to the interrupt source.
  • Once the ISR finishes, the microcontroller restores its state and resumes the main program from where it left off.

 

 

 

2. Describe the Interrupt handling mechanism in the 8051.

(6 Marks)

  • The 8051 has five interrupt sources:
    • INT0 and INT1: External hardware interrupts on pins P3.2 and P3.3.
    • TF0 and TF1: Timer overflow interrupts from Timer/Counter 0 and 1.
    • RI/TI: Serial communication interrupt for receive (RI) and transmit (TI) complete.
  • Each interrupt source has a corresponding bit in the Interrupt Enable (IE) register that controls whether the interrupt is enabled or disabled.
  • The Enable All (EA) bit in the IE register enables or disables the entire interrupt system.
  • The Interrupt Priority (IP) register defines the priority level for each interrupt, allowing high-priority interrupts to preempt lower-priority ones.

 

 

 

3. Explain the functionality of the following registers related to interrupts:

(a) IE Register

(6 Marks)

  • The Interrupt Enable (IE) register is an 8-bit register that controls the individual enabling/disabling of each interrupt source.
  • Setting a bit in the IE register enables the corresponding interrupt.
  • Clearing a bit disables the interrupt.
  • The EA bit in the IE register acts as a master switch for the entire interrupt system.
    • Setting EA = 1 enables all interrupts.
    • Clearing EA = 0 disables all interrupts (even if individual interrupt sources are enabled in their corresponding bits).

(b) IP Register

(6 Marks)

  • The Interrupt Priority (IP) register is an 8-bit register that defines the priority level for each interrupt source.
  • Setting a bit in the IP register assigns high priority to the corresponding interrupt.
  • Clearing a bit assigns low priority.
  • If two interrupts occur simultaneously, the high-priority interrupt will be serviced first.
  • If multiple interrupts have the same priority, the microcontroller uses an internal polling mechanism to determine which one to service.

 

 

 

4. Briefly describe the ADC0804 and the steps involved in interfacing it with the 8051 microcontroller.

(6 Marks)

  • The ADC0804 is an 8-bit Analog-to-Digital Converter (ADC) from National Semiconductor.
  • It converts an analog voltage input into a digital representation.

Interfacing Steps:

  1. Configure control signals (CS, WR, RD) for communication with the ADC.
  2. Initiate conversion by setting CS low and sending a pulse to WR.
  3. Check the INTR (Interrupt) pin to determine conversion completion.
    • If INTR = 1, conversion is ongoing (polling loop required).
    • If INTR = 0, conversion is complete.
  4. Read the converted digital data by setting CS low and pulsing RD.

 

 

 

 

5. Explain the concept of interfacing a stepper motor with the 8051 microcontroller.

(6 Marks)

  • A stepper motor rotates in discrete steps based on control signals.
  • The 8051 cannot provide enough current to drive a stepper motor directly.
  • A driver IC like ULN2003A is used to amplify the control signals from the 8051 to drive the stepper motor coils.
  • The 8051 sends digital control signals (0s and 1s) to the ULN2003A input pins.
  • The ULN2003A amplifies these signals and drives the corresponding stepper motor coils based on a specific sequence to achieve desired rotation

 

 

 

 

6. Describe the basic principles of interfacing a Liquid Crystal Display (LCD) with the 8051 microcontroller.

(6 Marks)

  • LCDs require specific control signals and data to display characters or graphics.
  • The 8051 communicates with the LCD using its parallel ports (P0 or P1 typically).
  • Control signals like Enable (E), Read/Write (R/W), Register Select (RS) are used to control the LCD's operation mode (data or instruction) and data transfer direction.
  • Data bytes are sent to the LCD's data pins (D0-D7) to display characters or define display settings.
  • A library function or custom code routine is used to handle communication and control the LCD for desired output.

 


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