MICROCONTROLLERS

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2 Marks & 16marks

UNIT-V

MICROCONTROLLERS

1. What is mean by microcontroller?

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 is called microcontroller.

2. Explain DJNZ instructions of intel 8051 microcontroller?

a) DJNZ Rn, rel

Decrement the content of the register Rn and jump if not zero.

b) DJNZ direct , rel

Decrement the content of direct 8-bit address and jump if not zero.

3. Write a program using 8051 assembly language to change the date 55H

stored in the lower byte of the data pointer register to AAH using rotate

instruction.

MOV DPL,#55H

MOV A, DPL

RL A

Label :SJMP label

4 Give the alternate functions for the port pins of port3?

RD – Read data control output.

WR – Write data control output.

T1 – Timer / Counter1 external input or test pin.

T0 – Timer / Counter0 external input or test pin.

INT1- Interrupt 1 input pin.

INT 0 – Interrupt 0 input pin.

TXD – Transmit data pin for serial port in UART mode.

RXD - Receive data pin for serial port in UART mode.

5 Specify the single instruction, which clears the most significant bit of B

register of 8051, without affecting the remaining bits.

Single instruction, which clears the most significant bit of B register of 8051,

without affecting the remaining bits is CLR B.7.

6. Explain the function of the pins PSEN and EA of 8051.

PSEN: PSEN stands for program store enable. In 8051 based system

in which an external ROM holds the program code, this pin is connected to the

OE pin of the ROM.

EA :EA stands for external access. When the EA pin is connected to Vcc,

program fetched to addresses 0000H through 0FFFH are directed to the internal

ROM and program fetches to addresses 1000H through FFFFH are directed to

external ROM/EPROM. When the EA pin is grounded, all addresses fetched by

program are directed to the external ROM/EPROM.

7. Explain the 16-bit registers DPTR and SP of 8051.

DPTR:

DPTR stands for data pointer. DPTR consists of a high byte (DPH) and a

low byte (DPL). Its function is to hold a 16-bit address. It may be manipulated as

a 16-bit data register or as two independent 8-bit registers. It serves as a base

register in indirect jumps, lookup table instructions and external data transfer.

SP:

SP stands for stack pointer. SP is a 8- bit wide register. It is incremented

before data is stored during PUSH and CALL instructions. The stack array can

reside anywhere in on-chip RAM. The stack pointer is initialised to 07H after a

reset. This causes the stack to begin at location

08H.

8 Name the special functions registers available in 8051.

• Accumulator

• B Register

• Program Status Word.

• Stack Pointer.

• Data Pointer.

• Port 0

• Port 1

• Port 2

• Port 3

• Interrupt priority control register.

• Interrupt enable control register.

9.Explain the register IE format of 8051.

EA- Enable all control bit.

ET2- Timer 2 interrupt enable bit.

ES – Enable serial port control bit.

ET1 – Enable Timer1 control bit.

EX1- Enable external interrupt1 control bit.

ET0 – Enable Timer0 control bit.

EX0- Enable external interrupt0 control bit.

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10.Name the five interrupt sources of 8051?.

The interrupts are:

Vector address

• External interrupt 0 : IE0 : 0003H

• Timer interrupt 0 : TF0 : 000BH

• External interrupt 1 : IE1 : 0013H

• Timer Interrupt 1 : TF1 : 001BH

• Serial Interrupt

Receive interrupt : RI : 0023H

Transmit interrupt: TI : 0023H

11.Explain the contents of the accumulator after the execution of the following

program segments:

MOV A,#3CH

MOV R4,#66H

ANL A,R4

A 3C

R4 66

A 24

12. Write a program to load accumulator A, DPH and DPL with 30H.

MOV A,#30

MOV DPH,A

MOV DPL,A

13.Write a program to subtract the contents of R1 of Bank0 from the contents

of R0 of Bank2.

MOV PSW,#10

MOV A,R0

MOV PSW,#00

SUBB A,R1

14. How the RS -232C serial bus is interfaced to 1TL logic device?

The RS-232C signal voltage levels are not compatible with TTL logic

levels. Hence for interfacing TTL devices to RS-232C serial bus, level converters are

used. The popularly used level converters are MC 1488 & MC 1489 or MAX 232.

15. List some of the features of 8096 microcontroller.

a. The 8096 is a 16-bit microcontroller.

b. The 8096 is designed to use in applications which require high speed

calculations and fast I/O operations.

c. The high speed I/O section of an 8096 includes a 16-bit timer, a 16-bit

counter, a 4 input programmable edge detector, 4 software timers and

a 6-output programmable event generator.

d. It has 100 instructions, which can operate on bit, byte, word, and

double words.

e. The bit operations are possible and these can be performed on any bit

in the register file or in the special function register.

16. List the features of 8051 microcontroller?

The features are

*single_ supply +5 volt operation using HMOS technology.

*4096 bytes program memory on chip(not on 8031)

*128 data memory on chip.

*Four register banks.

*Two multiple mode,16-bit timer/counter.

*Extensive Boolean processing capabilities.

*64 KB external RAM size

*32 bi-directional individually addressable I/O lines.

*8 bit CPU optimized for control applications.

17. What is the function of NEU?

The numeric execution unit executes all the instructions including arithmetic,

logical transcendental, and data transfer instructions.

The numeric execution unit executes all the numeric processor instructions while

the control unit (CU) receives, decodes instructions, reads and writes memory

operands and executes the 8087 control instructions.

18. Give the disadvantages of bus window technique?

The numeric execution unit executes all the instructions including arithmetic,

logical transcendental, and data transfer instructions.

The numeric execution unit executes all the numeric processor instructions while

the control unit (CU) receives, decodes instructions, reads and writes memory

operands and executes the 8087 control instructions.

19. What is swapping out?

A portion of the program or important partial results required for

further execution may e saved back on secondary storage to make the physical

memory free for further execution of another required portion of the program.

This is called ‘swapping out’ of the executable program.

20.List the features of 8051 microcontroller?

The features are

*single_supply +5 volt operation using HMOS technology.

*4096 bytes program memory on chip(not on 8031)

*128 data memory on chip.

*Four register banks.

*Two multiple mode,16-bit timer/counter.

*Extensive boolean processing capabilities.

*64 KB external RAM size

*32 bidirectional individually addressible I/O lines.

*8 bit CPU optimized for control applications.

21.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.

22 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 data bit go in to the RB8 in Special

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

programmable to either 1/32or1/64 the oscillator frequency.

23. Explain the mode3 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).In fact ,Mode3 is the same as Mode2 in all

respects except the baud rate. The baud rate in Mode3 is variable.

In all the four modes, transmission is initiated by any instruction

that uses SBUF as a destination register. Reception is initiated in Mode0 by

the condition RI=0&REN=1.Reception is initiated in other modes by the

incoming start bit if REN=1.

24.Explain the interrupts of 8051 microcontroller?

The interrupts are:

Vector address

• External interrupt 0 : IE0 : 0003H

• Timer interrupt 0 : TF0 : 000BH

• External interrupt 1 : IE1 : 0013H

• Timer Interrupt 1 : TF1 : 001BH

• Serial Interrupt

Receive interrupt : RI : 0023H

Transmit interrupt: TI : 0023H

25.Write A program to perfom multiplication of 2 nos using 8051?

MOV A,#data 1

MOV B,#data 2

MUL AB

MOV DPTR,#5000

MOV @DPTR,A(lower value)

INC DPTR

MOV A,B

MOVX @ DPTR,A

26.Write a program to mask the 0th &7th bit using 8051?

MOV A,#data

ANL A,#81

MOV DPTR,#4500

MOVX @DPTR,A

LOOP SJMP LOOP

27.List the addressing modes of 8051?

• Direct addressing

• Register addressing

• Register indirect addressing.

• Implicit addressing

• Immediate addressing

• Index addressing

• Bit addressing

28.Write about CALL statement in 8051?

There are two subroutine CALL instructions. They are

*LCALL(Long CALL)

*ACALL(Absolute CALL)

Each increments the PC to the 1st byte of the instruction & pushes them

in to the stack.

29.Write about the jump statement?

There are three forms of jump. They are

LJMP(Long jump)-address 16

AJMP(Absolute Jump)-address 11

SJMP(Short Jump)-relative address

30.Write program to load accumulator ,DPH,&DPL using 8051?

MOV A,#30

MOV DPH,A

MOV DPL,A

31.Write a program to find the 2’s complement using 8051?

MOV A,R0

CPL A

INC A

32.Write a program to add 2 8-bit numbers using 8051?

MOV A,#30H

ADD A,#50H

33.Write a program to swap two numbers using 8051?

MOV A, #data

SWAP A

34.Write a program to subtract 2 8-bit numbers &exchange the digits using

8051?

MOV A,#9F

MOV R0,#40

SUBB A,R0

SWAP A

35.Write a program to subtract the contents of R1 of Bank 0from the contents

of R0 of Bank 2 using 8051?

MOV PSW,#10

MOV A,R0

MOV PSW,#00

SUBB A,R1