EC65 04 - Microprocessor and Microcontrollerdmice.ac.in/wp-content/uploads/2017/05/Microprocessor-Microcontroller.pdf · 16. How is the memory segment accessed by 8086 microprocessor?

EC6504 – Microprocessor and Microcontroller V Semester – Question Bank

Department of Electronics and Communication Engineering 1

EC6504 - Microprocessor and Microcontroller

UNIT I

THE 8086 MICROPROCESSOR

1. What are different data transfer schemes?

The different data transfer schemes are [A/M – 12]

2. How is clock signal generated in 8086? What is the maximum internal clock frequency

of 8086? [N/D – 12]

The 8086 does not have on-chip clock generation circuit. Hence the clock generator chip,

8284 generates the CLK signal. The clock signal supplied by 8284 is divided by three for

internal use. The maximum internal clock frequency of 8086 is 5 MHz.

3. Write the function of queue status lines QS0 and QS1 in 8086 microprocessor.

The function of queue status lines QS0 and QS1 in 8086 microprocessor is to indicate the

activity in the queue during previous clock cycle. [N/D – 12]

4. What is a Microprocessor? What is the difference between Microprocessor and CPU?

DMI COLLEGE OF ENGINEERING



A microprocessor is a multipurpose, programmable logic device that accepts binary data as

input, processes data according to the instructions and provides output in binary form. It

reads binary instructions from a storage device called memory. The CPU is the unit that

includes ALU and control unit. Apart from processing the data, the CPU controls the entire

system functioning. Usually, a microprocessor will be the CPU of a system and it is called

the brain of the computer. [N/D – 11]

5. Why the program counter and the stack pointer registers are16 bits? [N/D – 11]

Program Counter (PC) and Stack Pointer (SP) are used to hold 16-bit memory addresses. PC

stores the 16-bit memory address of the next instruction to be fetched. SP points to the

beginning of stack memory. SP can be used to temporarily store the 16-bit memory address

as well as data. So, PC and SP are 16-bit registers.

6. What are Tristate devices?

A tri-state device is a digital device. The device is in the high state, the low state, or in a

high impedance state to prevent loading. This allows multiple circuits to share the same

output line or lines. [N/D – 10]

7. Draw the flag register for 8086.

The flag register of 8086 is given below:

Conditional Flags:



CF - Carry Flag

PF - Parity Flag

AF - Auxiliary Carry Flag

ZF - Zero Flag SF - Sign Flag

OF - Overflow Flag

Control Flags:

TF – Single step Trap Flag

IF – Interrupt Enable Flag

DF – String Direction Flag

8. What is the purpose of Bus Interface Unit?

The purpose of BIU is to interface 8086 with the outside world. It provides a 16-bit

bidirectional data bus and 20-bit address bus. This unit is responsible for performing

external bus operations. Functions

1. It fetches instruction from memory.

2. It reads data from port/memory.

3. It writes data into port/memory.

4. It supports instruction queuing.

5. It provides address relocation facility

9. Write the size of the data bus and address bus of 8086?

The size of data bus and address bus of 8086 are 16-bit and 20-bit respectively.

10. What is the function of an accumulator?

Accumulator is a tri-state eight bit register. It is extensively used in arithmetic, logic, load

and store operations, as well as in input/output (I/O) operations. The result of arithmetic and

logical operations is stored in the register A. Hence, it is also identified as accumulator.

11. What is the clock frequency of 8086?

The maximum internal clock frequency of 8086 is 5 MHz.

12. What is memory segmentation?



Memory segmentation is dividing the linear memory space into “chunks” called segments.

8086 segmented memory system has four segments Code segment, Data segment, Extra

segment, and Stack segment.

13. What is pipelining?

In 8086, to speed up the execution of program, the instructions fetching and execution of

instructions are overlapped each other. This technique is known as pipelining. In pipelining,

when the n th instruction is executed, the n+1 th instruction is fetched and thus the

processing speed is increased.

14. What is meant by physical addressing in 8086?

Physical addressing is used to address 1MB memory of 8086. The 8086 memory address is

20 bits but all the registers used for memory calculation are of 16 bit length. The 20 bit

physical address is computed by summing the contents of the segment register (shifted left

by 4 bits) and an effective (offset) address. The segment register holds the upper 16 bits of

the 20 bit memory address. The effective address represents the offset from the starting

address of the segment Eg: (CS x 10H ) + IP = Physical address CS is shifted left by 4 bit

and summed with IP (offset) to compute physical address.

15. Define – Segment Override Prefix

The segment override prefix allows the programmer to deviate from the default segment. It

is an additional 8-bit code selects the alternate segment register. The code byte for the

segment override prefix as the format 001XX110. The XX represents 2 bits which are as

follow: ES = 00, CS = 01, SS = 10, DS = 11.

16. How is the memory segment accessed by 8086 microprocessor? [A/M – 11]

The memory segment accessed by 8086 microprocessor is identified by the status of the

status bits S3, S4. The Status bits S3, S4 when decoded, indicate the type of operation

(memory access) being performed and the segment register being used.



UNIT II

8086 SYSTEM BUS STRUCTURE

1. What is the function of the signal in 8086?

BHE signal means Bus High Enable signal. The BHE signal is made low when there is some

read or write operation is carried out. ie . When ever the data bus of the system is busy i.e.

whenever there is some data transfer then the BHE signal is made low.

2. State the significance of LOCK signal in 8086.

If 8086 is working at maximum mode, there are multiprocessors are present. If the system

bus is given to a processor then the LOCK signal is made low. That means the system bus is

busy and it cannot be given of any other processors. After the use of the system bus again the

LOCK signal is made high.

That means it is ready to give the system bus to any processor.

3. What are the functions of bus interface unit (BIU) in 8086?

(a) Fetch instructions from memory.

(b) Fetch data from memory and I/O ports.

(c) Write data to memory and I/O ports.

(d) To communicate with outside world.

(e) Provide external bus operations and bus control signals.

4. What are the two modes of operations present in 8086?

i. Minimum mode (or) Uniprocessor system

ii. Maximum mode (or) Multiprocessor system

5. What is multiprogramming?

If more than one process is carried out at the same time, then it is known as



multiprogramming. Another definition is the interleaving of CPU and I/O operations among

several programs is called multiprogramming.

To improve the utilization of CPU and I/O devices, we are designing to process a set of

independent programs concurrently by a single CPU. This technique is known as

multiprogramming

6. What is the importance of 𝑰𝑵𝑻𝑨̅̅ ̅̅ ̅̅ ̅̅ ?

Interrupt Acknowledge generated by the microprocessor in response to INTR. Causes the

interrupt vector to be put onto the data bus.

7. Under what conditions can bus contention occurs?How does a tri-state buffer help avoid

this problem?

Bus contention occurs when two outputs attempting to control the same line. It can be

avoided by tri-state buffer can be turned off

8. List the chips and their function required to design maximum mode single-processor

8086 CPU module.

1.8284A clock generator

2.8288 bus controller

3.8282/83 bus duffers

4.8286/87 address latches

9. What are the advantages of multiprocessor system?

• High level performance can be attained when parallel processing.

• Robustness can be improved by isolating system functions.

10. What are the problems occurred in multiprocessor system?

1. Bus contention

2. Interprocess communication

3. Resource sharing

11. What is Coprocessor?



The coprocessor is a processor which specially designed for processor to work under the

control of the processor and support special processing capabilities.

Example : 8087 which has numeric processing capability and works under 8086.

12. What are the basic multiprocessor configurations?

1. Coprocessor configuration

2. Closely Coupled configuration

13. What are the schemes for establishing priority in order to resolve bus arbitration

problem?

There are three basic bus access control and arbitration schemes

1. Daisy Chaining

2. Independent Request

3. Polling

14. Compare closely coupled and loosely coupled configurations.

Closely coupled

Loosely coupled

1. Single CPU is used

1. Multiple CPU modules are

used

2. It has local bus only

2. It has local as well system

bus

3. No system memory or IO

3. It has system memory and

IO, shared among CPU

modules



4. No bus arbitration logic

required

4. Bus arbitration logic

required

15. What is mean by loosely coupled multiprocessor system?

In loosely coupled multiprocessor system, each processor has a set of Input/output

devices and a large memory, where it accesses most of the instructions and data.

16. Write the advantages of loosely coupled system over tightly coupled systems?

1. More number of CPUs can be added in a loosely coupled system to improve the

system performance

2. The system structure is modular and hence easy to maintain and troubleshoot.

3. A fault in a single module does not lead to a complete system breakdown.



UNIT III

I/O INTERFACING

1. What are the modes of operation supported by 8255?

The modes of operations supported by 8255 are:

1. I/O Mode (Input / Output mode)

a) Mode 0 – Simple I/O

b) Mode 1 – Handshaking or Strobed I/O mode

c) Mode 2 – Strobed bidirectional I/O Mode

2. BSR Mode (Bit set / reset mode )

2. What are the enhanced features of 8254 Programmable Interval Timer compared with

8253? [N/D – 12]

The enhanced features of 8254 Programmable Interval Timer compared with 8253 are:

1. Operating frequency 0 – 10 MHz.

2. Uses H-MOS technology.

3. Read-Back command is available.

4. Reads and writes of the same counter can be interleaved.

3. What are the functions of the scan section in 8279? [A/M – 11]

The functions of scan counter in scan section are: 1. To scan the key matrix (keyboard) 2. To

refresh the display In encoded mode scan counter provides a binary count from 0000 to 1111

on four scan lines (SC 3 – SC 0) with active high outputs. In decoded mode scan counter

decodes least significant 2 bits of binary counts and provides 4 possible combinations on scan

lines (SC3 – SC0): 1110, 1101, 1011, and 0111.



4. To which port of the CPU is CRT monitor and printer connected? [N/D – 11]

The CPU is connected to CRT monitor through serial port using RS232 interface. The printer

is connected to CPU through serial interface (serial port) using RS232 interface or parallel

interface through parallel port (8255).

5. What is the operating frequency of 8279?

The required internal operating frequency of 8279 is 100 KHz to a maximum of 3 MHz.

6. What is Key debounce?

Key debounce is the minimum time that the microprocessor must wait for the key to reach

steady state when a key is pressed. Mechanical switches are used as keys in most of the

keyboards. When a key is pressed, the contact bounces back and forth and settles down only

after a small time delay (about 20 ms).

7. Compare the features of A/D converter with D/A converter. [N/D – 11]

A/D converter D/A converter

1 An analog-to-digital converter (abbreviated

ADC, A/D or A to D) converts a continuous

physical quantity (usually voltage) to an

equivalent digital value.

A digital-to-analog

converter (abbreviated

DAC, D/A) translates

digital information into

equivalent Analog

quantity (voltage or

current).

2 The basic techniques include ramp,

integrating ramp, successive approximation.

The basic technique

include decoder

resistance network.

8. Define – Resolution of ADC [M/J – 12]

Resolution is defined as the minimum change in voltage (input) required to guarantee a

change in the output code level. The resolution Q of the ADC is equal to the LSB voltage. The

voltage resolution of an ADC is equal to its overall voltage measurement range divided by the



number of discrete values. It is expressed in volts.

EFSR is the full scale voltage range. M is the number of bits in an M bit ADC.

9. What is the function of sample and hold circuit? [A/M – 11][N/D – 10] [M/J – 12]

A sample and hold circuit is a circuit which samples an input signal, and holds on to its last

sampled value until the input is sampled again. Sample and hold circuits are commonly used

in analog to digital converter, communication circuits, PWM circuits, etc.

10. List out the major functions performed by CRT interface. [A/M – 11]

The major functions performed by CRT interface are:

1. CRT terminals work on RS232 C interface.

2. CRT interface transmits and receives the binary data serially with fixed baud rate.

3. CRT interface has three terminals TXD, RXD, GND.

4. TXD is used for data transmission from CRT to microprocessor.

5. RXD is used for data transmission from microprocessor to CRT.

6. GND is used for common ground.

11. What are the functional types used in control words of 8251A ?

The control words of 8251A are divided into two functional types.

1. Mode Instruction control word 2. Command

Instruction control word Mode Instruction control word :-This defines the general

operational characteristics of 8251A.

2.Command Instruction control word:-The command

instruction controls the actual operations of the selected format like enable transmit/receive,

error reset and modem control

.

12. Write the features of mode 0 in 8255?

1. Two 8-bit ports (port A and port B) and two 4-bit ports (port C upper and lower) are

available. The two 4-bit ports can be combined used as a third 8-bit port.

2. Any port can be used as an input or output port.

3.Output ports are latched. Input ports are not latched.

4. A maximum of four ports are available so that overall 16 I/O configurations are possible.



13. What are the features used mode 1 in 8255?

Two groups – group A and group B are available for strobed data transfer.

1. Each group contains one 8-bit data I/O port and one 4-bit control/data port.

2. The 8-bit data port can be either used as input or output port. The inputs and outputs both

are latched.

3. Out of 8-bit port C, PC0-PC2 is used to generate control signals for port B and PC3=PC5

are used to generate control signals for port A. The lines PC6, PC7 may be used as

independent data lines.

14. What is the function of mode set register in 8257?

The mode set register is used for programming the 8257 as per the requirements of the

system. The function of the mode set register is to enable the DMA channels individually

and also to set the various modes of operation.



UNIT IV

MICROCONTROLLER

1. What is a microcontroller?

Microcontroller is a device which contains the microprocessor with integrated

peripherals like memory, serial ports, parallel ports, timer/counter, interrupt controller,

data acquisition interfaces like ADC, DAC.

2. What happens in power down mode of 8051 microcontroller?

[M/J – 13 ][A/M – 11 ]

The microcontroller enters power down mode by setting the PD bit to 1. The following

happens in power down mode of 8051 microcontroller:

a) The internal clock to the entire microcontroller is stopped. However, the program

is not dead.

b) Vcc can be reduced to as low as 2V in power down mode.

c) The internal RAM gets it back up supply from RST/VPD pin.

d) Port values are not changed /overwritten in power down mode.

3. What is the size of memory systems used in 8051 microcontroller? [N/D – 12]

The size of the memory systems in 8051 microcontroller are:

External program memory (ROM) – 64 Kbytes

External data memory (RAM) – 64 Kbytes

Internal ROM – 4 Kbytes

Internal RAM – 128 bytes



4. What is the function of RS1 and RS0 bits in the flag register of Intel 8051

microcontroller?

The function of RS1 and RS0 bits in the flag register is to select the register bank.

RS1, RS0 – Register bank select bits

5. List out the applications of 8051 microcontroller.

The applications of 8051 microcontroller are

Control applications:

Office automation, home automation and industrial automation.

Embedded applications:

Since, it is single chip controller, 8051 microcontrollers are much useful in all embedded

applications like real time, wireless modes.

Network applications:

In the area of wireless networking, including LAN, MAN, and WAN.

Common applications:

Used in the measurement of frequency, reactance, voltage, current, resistance,

temperature, strain management, etc. It is also used in delay subroutine, LED display,

relays, and for interfacing with other electronic components.

6. List out the advantages of general purpose registers / register banks.

The advantages of general purpose registers are:

a) Used by programmers

RS1

RS0 Bank Selection Address

0 0 Bank 0 00h – 07h

0 1 Bank 1 08h – 0Fh

1 0 Bank 2 10h – 17h

1 1 Bank 3 18h – 1Fh



b) Default power setup

c) Less processing time

7. What is PSW?

PSW (Program Status Word register) is an 8 bit register that contains the status of the

program information.

PSW consists of 4 types of flags namely carry, auxiliary carry, overflow and parity flag.

PSW is bit addressable register.

It is used to select the register bank (RS1 and RS0).

C AC F0 RS1 RS2 OV - P

8. What is the size of internal RAM and ROM of 8051?

The size of internal RAM and ROM of 8051 microcontroller are:

Internal ROM – 4 Kbytes

Internal RAM – 128 bytes

9. List out the flags available in 8051.

The flags available in 8051 are:

Four mathematical flags, Carry (CY), Auxiliary Carry (AC), Overflow Flag (OF) and

Parity flag (P) specified in PSW register.

Two general purpose flags GF0 and GF1 in the PCON register.

10. What is meant by Power On Reset in 8051?

Power On Reset in 8051 will reset the microcontroller and terminate all activities. It also

causes all values in the register to be lost. The reset pin in 8051 is pin 9. It is normally

low. Upon applying high pulse to this pin, power on reset is activated.

11. What is the need for bitwise instructions in microcontroller? [M/J – 12]

Bitwise instructions are needed in microcontroller for the following reasons:

1. Sometimes only 1 or 2 bits of the port are to be accessed instead of entire 8

bits without altering the rest of the bits in the port.



2. It requires discrete input and output bits, to control or detect the logic state of

devices like switches, LEDs, LCD displays and sensors for data such as

temperature, humidity, light level etc.

3. Since, microcontrollers are used in automatically controlled products and

devices, such as appliances, toys and other embedded systems.

12. What are the operand types used in 8051 microcontroller? [N/D – 12]

The different operand types used in 8051 microcontroller are:

Immediate operand

a) Register

b) Memory

13. What are the different ways of operand addressing in 8051? [A/M – 11]

The different ways of operand addressing in 8051 are:

a) Immediate addressing

b) Register addressing

c) Direct addressing

d) Indirect addressing

e) Relative addressing

f) Index addressing

14. What are the advantages of the register indirect addressing mode in 8051

microcontroller? [N/D – 10]

The advantages of the register indirect addressing mode in 8051 microcontroller are:

a. It makes accessing data dynamic rather than static as in the case of direct

addressing mode.

b. Looping is possible in register indirect addressing mode.



15. Write an 8051 program to monitor P1 continuously. It should get out of the

monitoring only if P1 = 63H. [N/D – 10]

MOV P1, # 0FFh

LABEL: MOV A, P1

CJNE A, # 63,

LABEL HERE: SJMP HERE

16. List out the special function registers used for port operation in 8051? [M/J – 12 ]

The special function registers used for port operation in 8051 are P0, P1, P2, and P3.

Each port are 8 bit wide which are bit addressable i.e. each bit can be set or reset by the

bit instructions (SETB for high, CLR for low) independently. The address of

1. Port 0 is 80

2. Port 1 is 90

3. Port 2 is A0

4. Port 3 is B0

17. What are the hardware and software interrupts of 8051 μc? Write its vector

address. [N/D – 11 ]

The hardware and software interrupts of 8051 μc are:

External hardware interrupt 0 (INT0) – 0003H

External hardware interrupt 1 (INT1) – 0013H

Timer 0 interrupt (TF0) – 000BH

Timer 1 interrupt (TF1) – 001BH

Serial port interrupt (RI or TI) – 0023H

18. How many ports are bit addressable in 8051 microcontroller? [N/D – 11]

All the ports (Port 0 to Port 3) are bit addressable in 8051 Microcontroller.

19. List out the timers available in 8051.



The timers available in 8051 are

Timer 0 (T0) – 16 bit timer / counter

Timer 1 (T1)– 16 bit timer / counter

These two timers can be configured either as timers or event counters. They can be split

into two byte register namely TL0, TH0, TL1, and TH1.

20. What is the function of SCON register?

The SCON register is an 8 bit register used to program the start bit, stop bit, and data bit

of the data framing. The following format describes the various bits

D7 D6 D5 D4 D3 D2 D1 D0

SM0 SM1 SM2 REN TB8 RB8 TI RI

SM0 SM1 MODE

0 0 Serial Mode 0

0 1 Serial Mode 1

1 0 Serial Mode 2

1 1 Serial Mode 3

SM2: 1 – for multiprocessor communication

0 – for single processor

REN: SET/CLEAR by software to enable or disable reception

TB8: Transmit bit for serial mode 2 and 3

RB8: Receive bit for serial mode 2 and 3

21. What is the function of PCON register?

The function of PCON register is to select the power modes in 8051.The configuration



of (PCON) power control register is shown below:

SMOD: Serial baud rate modify bit

GF1 : General purpose user flag bit 1

GF0 : General purpose user flag bit 0

PD : Power down bit

IDL : Idle mode bit

UNIT V

INTERFACING MICROCONTROLLER

1. List the modes of Timer in 8051.

The modes of timer in 8051 are chosen with the help of two bits,viz., M0 & M1 in TMOD register.

M1 MO Mode Description of Timer

0 0 0 13-bit timer

0 1 1 16-bit timer

1 0 2 8-bit timer with auto reload

1 1 3 Split timer

2. What is the significance of C/T bit in TMOD register of 8051?

The C/T bit in the TMOD register is a selector bit for the type of operation to perform in the timer

register.

HIGH in that bit indicates Counter operation and LOW in that bit indicates Timer operation.

0 Timer Operation

1 Counter Operation

3. What is the significance of TRx bit in TCON register of 8051?

TRx bit in the TCON register is used to Start / Stop the timer register for both timer and counter

operation, by setting that bit with value ‘1’ or ‘0’.



4. Explain the Timer operation of 8051.

In this mode, the timer register is used to generate the time delay using theclock signal

applied to the processor.An initial count is loaded in the timer register. When the timer is

started, thetimer register content gets incremented after every machine cycle. When thetimer

register crosses (i.e., overflows) the count FFFFH and goes to 0000H,the timer overflow flag in

TCON register becomes set.Hence, by loading appropriate value in the timer register, a specific

timedelay can be generated using timer. One machine cycle consists of 12 clocksignal

periods and the delay is equal to count value loaded * time period of one machine cycle

5. List the Interrupt sources in 8051.

The Six Interrupt sources in 8051 are

•RESET

•INT0, INT1

•TF0, TF1

•SPI (TI/RI)

6. What are the types of serial communication?

The serial communication can be,

•Synchronous (continuous)

•Iso-Synchronous (with regular time intervals)

•Asynchronous (with irregular time intervals)

7. Define Baud rate.

It is the speed of serial data transfer, expressed in bits/sec.The standard baud rates are110, 150,

300, 600, 1200, 2400, 4800, 9600, 19200…

8. Explain the operating mode2 of 8051 serial ports.

In this mode 11 bits are transmitted(through TXD)or received (through RXD):a start bit(0), 8

data bits(LSB first),a programmable 9th data bit ,& a stop bit(1).ON transmit the 9th data bit

(TB* in SCON)can be assigned the value of 0 or 1.Or for eg:, the parity bit(P, in the

PSW)could be moved into TB8.On receive the 9th d ata bit go in to the RB8 in Special

Function Register SCON, while the stop bit is ignored. The baud rate is programmable to



either 1/32 or 1/64 the oscillator frequency.

9. Explain the operating mode0 of 8051 serial ports.

In this mode serial enters &exits through RXD, TXD outputs the shift clock.8 bits are

transmitted/received:8 data bits(LSB first).The baud rate is fixed at 1/12 the oscillator

frequency.

10. What are the tasks involved in keyboard interfacing?

The task involved in keyboard interfacing are sensing a keyboard interfacing are sensing

a key actuation, de bouncing the key and generating key codes(decoding the key).these task

are performed software if the keyboard is interfaced through ports and they are performed

by hardware if the keyboard is interfaced through 8279.

11. How a keyboard matrix is formed in keyboard interface ?

The return lines RL0 to RL7 of 8279 are used to form the columns of keyboard matrix.in

decoded scan the scan lines SLO to SL3 of 8279 are used to form the rows of keyboard

matrix. In encoded scan mode, the output lines of external decoder are used as rows of

keyboard matrix.

12. What is scanning in keyboard and what is scan time?

The process of sending a zero to each row of a keyboard matrix and reading the columns

for key actuation is called scanning. the scan time is the time taken by the processor to scan

all the rows one by one starting from first row and coming back to the first row.

13. What is scanning in display and what is the scan time?

In display devices the process of sending display codes to 7-segment LED’S to display the

led’s one by one is called scanning. The scan time is the time taken to display all the 7-

segment LED’S one by one, starting from first LED and coming back to the first LED

again.



Documents

EC65 04 - Microprocessor and Microcontrollerdmice.ac.in/wp-content/uploads/2017/05/Microprocessor-Microcontroller.pdf · 16. How is the memory segment accessed by 8086 microprocessor?