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Chapter: Microprocessor and Microcontroller : Interfacing Microcontroller

Important Short Questions and Answers: Interfacing Microcontroller

Microprocessor and Microcontroller - Interfacing Microcontroller - Important Short Questions and Answers: Interfacing Microcontroller



1. What is a serial data buffer?


Serial data buffer is a special function register and it initiates serial transmission when byte is written to it and if read, it reads received serial data.


It contains two independent registers internally.


One of them is a transmit buffer, which is a parallel-in serial-out register. The other is a receive buffer, which is a serial-in parallel-out register

2. What are timer registers?


Timer registers are two 16-bit registers and can be accessed as their lower and upper bytes. TLO represents the lower byte of the timing register 0, while THO represents higher bytes of the timing register 0. Similarly, TLI and THI represent lower and higher bytes of timing register 1. These registers can be accessed using the four addresses allotted to them, which lie in the special function registers address range, i.e., 801 H to FF.

3. What is the use of timing and control unit?


Timing and control unit is used to derive all the necessary timing and control signals required for the internal operation of the circuit. It also derives control signals that are required for controlling the external system bus.


4. When are timer overflow bits set and reset?


The timer overflow bits are set when timer rolls over and reset either by the execution of an RET instruction or by software, manually clearing the bits. The bits are located in the TCON register along with timer run control (TRn) bits.


5. Explain the mode (0 and1) operation of the timer. The operations are as follows:

• Timer mode 0 and 1 operations are similar for the 13 bit (mode) or 16 bit (mode 1) counter. When the timer reaches the limits of the count, the overflow flag is set and the counter is reset back to zero.

The modes 0 and 1 can be used to time external events.


They can be used as specific time delays by loading them with an initial value before allowing them to


execute and overflow.


6. What is the different modes in which timer 2 can operate?


The two different modes in which Timer 2 operates are. i. Capture mode


Timer 2 operates as free running clocks, which saves the timers value on each high to low transition. It can be used for recording bit lengths when receiving Manchester-encoded data.


ii. Auto-reload mode:


When the timer overflows, value is written into TH2/TL2 registers from RCA P2H/RCA P21 registers. This feature is used to implement a system watch dog timer.


7. What ia the use of a watch dog timer?


A watching timer is used to protect an application in case the controlling microcontroller begins to run amok and execute randomly rather than the preprogrammed instructions written for the application.


8. Define interrupt.


Interrupt is defined as request that can be refused. If not refused and when an interrupt request is acknowledged, a special set of routine or events are followed to handle the interrupt.


7. What are the steps followed to service an interrupt? The steps followed are:

I. Save the context register information.

II. Reset the hardware requesting the interrupt.


III. Reset the interrupt controller.

IV. Process the interrupt.

V. Restore the context information.

VI. Return to the previously executing code.


8. How can 8051 be interrupted?


There are five different ways to interrupt 8051. Two of these are from external electrical signals. The other three are caused by internal 8051 I/O hardware operations.


9.Give the format of the interrupt enable register. The format of the interrupt enable register is, EA - - ES ET1 EX1 ET0 EX0


The register is used to enable or disable all 8051 interrupts and to selectively enable or disable each of the five different interrupts.


EA: Disables all interrupts

Es: Enables or disable the serial port interrupt.


ET1: Enable or disable the timer 1 overflow interrupt. EX1: Enable or disable external interrupt 1.


ET0: Enable or disable the timer 0 overflow interrupt. EX0: Enable or disable external interrupt 0.


10. What is meant by nesting of interrupts?


Nesting of interrupts means that interrupts are re-enabled inside an interrupt handler. If another interrupt request codes in, while the first interrupt handler is executing, processor execution will acknowledge the new interrupt and jump to its vector.


11. How is the 8051 serial port different from other micro controllers?


The 8051 serial port is a very complex peripheral and able to send data synchronously and asynchronously in a variety of different transmission modes.


12. Explain synchronous data transmission.


In synchronous mode (mode 0), the instruction clock is used.

Data transfer is initiated by writing to the serial data port address.

Txd pin is used for clock output, while Rxd pin is for data transfer.

When a character is received, the status of the data transfer is monitored by polling the RI-n bit in serial


control register (SCON).


13. Give an application for synchronous serial communiction.

An application for synchronous serial communication is RS – 232.


14. When is an external memory access generated in 8051?

In 8051, during execution the data is fetched continuous. Most of the data is executed out of the 8051‟s built-in control store. When an address is outside the internal control store, an external memory access is generated.


15.Give the priority level of the interrupt sources. Interrupt source Priority within a level IE0 (External INT0 )

TF0(Timer 0)


IE 1 (External INT 1) TF 1 (Timer 1)


RI = TI (Serial port) Highest






16. What is the use of stepper motor?

A stepper motor is a device used to obtain an accurate position control of


rotating shafts. A stepper motor employs rotation of its shaft in terms of steps, rather than continuous rotation as in case of AC or DC motor.


17. What is meant by key bouncing?

Microprocessor must wait until the key reach to a steady state; this is known as Key bounce


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