KONGHU VELALAR POLYTECHNIC COLLEGEMICROCONTROLLER QUESTION BANK

UNIT I1. Define microcontroller. Microcontroller is a complete microcomputer on a chip. It is a digital IC fabricated by using VLSI technology. It contains serial and parallel I/O ports, RAM and ROM types of memory, timer/counters, interrupt controls etc. 2. How many I/O ports are placed in microcontroller 8051?

The 8051 has 32 I/O pins configured as four 8 bit parallel ports (P0, P1, P2, P3).3. Advantages of microcontroller. As the peripherals are integrated into a single chip, the overall system cost is very low. The product is of a small size as compared to the microprocessor based system and is thus very handy. Easyto troubleshoot. Morereliable. All these features are available in a 40 pin package as in an 8 bit processor. 3.Features of microcontroller. 8 bit CPU. On chip oscillator and clock circuitry. 32 I/O lines. 64 Kbyte address space for external data memory. 64Kbyte address space for external program memory. 4. Disadvantages of microcontroller. Learn large instruction set. Limited calculation procedure. Fixed programming technique to control machine. 5.Applications of microcontroller. Small business system. Office automation. Entertainment. Trafficcontrol. 6. Write short notes on 8051. The microcontroller 8051 is a second generation 8-bit microcontroller. It is a single chip 40 pin DIP IC. It provides more powerful architecture, more powerful instruction set. It operates +5V dc supply.7. Define program status word (PSW). It is one of the special function register. This register contains program status information. It is a bit and byte addressable register.D7 D6 D5 D4 D3 D2 D1 D0CY AC F0 RS1 RS0 OV -- P

8. Define stack pointer.This register is an 8-bit register. The stack may reside anywhere in on-chip RAM. It is incremented before data is stored during PUSH and CALL executions. it is decremented after data is retrieve from memory during POP and RET execution. After, the stack pointer is initialized to 07H.this causes thestack begins at location 08H.9. Define data pointer. It is a 16 bit register. This register contains a higher byte (DPH) and lower byte (DPL) 8 bit registers. It may be manipulated as a 16 bit register or as two 8 bit registers. 10. Define serial data buffer. The serial data buffer contains two independent registers of a transmit buffer register and a receive buffer register.when data is moved to SBUF,it goes to transmit buffer,where it is held for serial communication.when data is moved from SBUF ,it comes from the receive buffer.11. Define timer registers/How many timer/counters are placed in 8051. Microcontroller 8051 has two 16-bit timer/counter registers. They are timer 0 and timer 1. They are specified as two Register pairs (TH0, TL0) and (TH1, TL1). 12. Define control registers. The special function registers IP, IE, TMOD, TCON, SCON and PCON contain control and status information for interrupts,timer/counters and serial port.so,these registers are called control registers.13. Write about oscillator.This circuit generates the basic timing clock signal for the operation of the circuit using crystal oscillator.14. Write about internal RAM and ROM capacity of 8051. Data memory-internal RAM (256 Bytes). External RAM (64Kbytes). Program memory-internal ROM (4Kbytes), external ROM (64Kbytss). 15. Define program counter of 8051. The program instruction bytes fetched from locations in memory that are addressed by the program counter. The pc is automatically incremented after every instruction byte is fetched and may also be altered by certain instructions. 16. Classify types of I/O ports in 8051.8051 contains 4 I/O ports. Each port has 8 I/O lines. All ports are bi-directional. They are port 0 port 1 port 2 port 3. 17. Define timer. The counter is programmed to count the internal clock pulses, and then it is known as timer.18. Write about 8051 timer functions.In the timer function, the register is incremented every machine cycle. That means in timer operation it counts the machine cycles. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of oscillator frequency.19. Define counter.The counter is programmed to count the external clock pulses, then it is known a counter.20. Write about 8051 counter functions.In the counter function, the register is incremented in response to 1 to 0 transition at its corresponding external input pin T0 or T1.since it takes at least 2 machine cycles (24 oscillator periods) to recognize a 1 to transition. The maximum count rate is 1/24 of the oscillator frequency (fosc/24).21. How many clock cycles and states are placed in one machine cycle.In 8085 1 machine cycle consists 6 states, each state having 2 clock cycles. Therefore one machine cycle consists of 12 clock cycles.22. Define clock cycle.The square wave generated by the clock sources are called as clock cycles. 23. Define machine cycle of 8051.

Certain numbers of clock cycles are required to execute an instruction. These clock cycles are called as machine cycle. One machine cycle is 8051 was made up of six states.24. Define state.A state is the time interval required for the discrete operations of the microcontroller such as fetching an opcode, decoding an opcode or writing a data byte to memory. Each state consists of two oscillator pulses (clock cycles).25. Define instruction cycle.

The time required to fetch and execute an instruction is called as instruction cycle.Instruction cycle = fetch cycle + execute cycle. 26. How many instructions in 8051 microcontroller.The 8051 instruction set includes 111 instructions, 49 of which are single byte, 45 two byte and 17 three byte instructions.27. Classify the instruction set of 8051. Data transfer instructions Arithmetic instructions Logical instructions Control transfer instructions Bit manipulation instructions. 28. Classify the three types of data transfer instructions in 8051. i.General purpose instructions. ii.Accumulator specific instructions and iii.Address specific data transfer instructions. 29. Write the types of general purpose data transfer instructions. MOV Instructions PUSH Instructions POP instructions 30. Write the types of accumulator specific data transfer instructions. The accumulator specific data transfer instructions move data into and out of the accumulator. There are four types of instructions,i).XCH, ii).XCHD, iii).MOVX, iv).MOVC.31. Write the types of address specific data transfer instructions.This instruction is used to load 16-bits of address/data into the data pointer.

MOV DPTR,#address.32. Write some byte level data transfer instructions.The data transfer instructions moves data from source operand to destination operand. Actually the copy of the data is moved from one place to another place.Ex: MOV A,RnThe content of the register Rn is copied into the Accumulator.

MOV Rn, #dataThe content of the second byte of the instruction is copied into the Register Rn.33. Write some bit level instructions MOV C, bit

The content of the directly addressed bit is copied into the carry flag.

MOV bit, C

The content of the carry bit is copied into the directly addressed bit. 34. Define addition with examples.ADD: This type of instruction adds the content of the accumulator to the content of source operand and puts the result in accumulator.

ADD A, RnThe content of register Rn is added with the content of Accumulator and the result is stored in the accumulator.

ADD A, #dataThe content of second byte of the instruction is added with the content of accumulator and the result is stored in accumulator.35. Define addition with Carry. Give some Examples.

This type of instruction adds the content of accumulator and the content of Carry flag with the content of source operand and puts the result in the accumulator.Ex: ADDC A, RnThe content of register Rn and the content of carry flag, both are added with the content of Accumulator, and the result is stored in accumulator.36. Define SUBB with examplesSUBB(Subtraction with borrow): This type of instructions subtracts the content of second source operand and the content of Carry flag from the content of accumulator. Stored result in the accumulator. Ex: SUBB A, RnThe content of register Rn and the content of carry flag both are subtracted from the content of accumulator and the result is stored in the accumulator.37. Define increment and decrement with exampleINC: This type of instruction adds one to the content of source operand, and puts the result in the same operand. Ex: INC AThe content of accumulator is increment by one.DEC: This type of Instructions subtracts one from the content of source operand and stores the result in same operand. Ex: DEC RnThe content of Rn is decremented by one.38. Define Multiplication with Example.MUL instruction performs an unsigned multiplication of the A register by the B register ,and produces a double byte result .ACC receives the low order byte,and B receives the higher order byte.

Ex:MUL ABThe content of Accumulator is multiplied with the content of B register .After multiplication lower order result stored in Accumulator, higher order result is stored in B register.39. Define division with example.DIV instruction performs an unsigned division of the register A and B register. After division quotient is stored in A register and the remainder is stored in B register.Ex:DIV ABThe content of Accumulator is divided by content of B register .After division, the quotient is stored in A register and remainder is stored in B register.40. Draw the table to show the flags are affected during the execution of arithmetic instructions.S.NOINSTRUCTIONSFLAG

COAC

1.ADDYV

XXX

2.ADDCXXX

3.SUBBXXX

4.MUL0X--

5.DIV0X--

6.DAX----

41. Write short notes on overflow problem.If the result of operations is too large then an overflow has occurred. The programmer has to monitor the overflow flag while operating the signed numbers.In the 8 bit signed number operation, the OV is set for following two conditions:i.A carry from D6 to D7 bit, but no carry from D7 bit.ii.A carry from D7(cy=1),but no carry from D6 to D7 bit.(if there is a carry both from D6 to D7 bit and from D7 out(cy=1),then OV = 0 (overflow will not set)).42. Classify the two types of logical instructions.The microcontroller 8051 performs basic logic operations on both bit and byte operands. It is classified in to two types,I. single operand instruction,II. Two operand instruction.43. Write about single operand instructions. CLR instructions set Acc, Carry flag or any directly addressable bit to zero. SETB instructions sets carry flag or directly addressable bit to 1. CPL instruction is used to complement the content of Acc without affecting any flags, Carryflag or directly addressable bit location. RL,RLC,RR,RRC and SWAP are the five rotate instructions that can be performed on Acc.RL rotates left,RR rotates right,RLC rotates left through carry,RRC rotates right through carry and SWAP rotates left through four bits. 44. Write about two operand instructions. ANL (AND Logic) instructions perform bit level and byte level AND logic functions. The result is returned to the first operand. ORL (OR Logic) instructions perform bit level and byte level OR logic functions. The result is returned to the first operand. XRL (Ex-OR logic) instructions perform byte level Exclusive OR logic function. The result is returned to the first operand. 45. Give some example for byte level logical instructions. ANL A,Rn; the content of register Rn is logically ANDed with the content of accumulator, and the result is stored in Accumulator.ORL A, direct: the content of directly specified location is logically OR ed with the content of Accumulator, and the result is stored in accumulator.XRL A,@Ri: the content of memory location addressed by register Ri is logically Exclusive OR ed with the content of accumulator, and the result is stored in Accumulator.CLR A,CPL A,RL A,RLC A,RRA,RRC A,SWAP A.46. Give some examples for bit level logical instructions.CLR C:carry flag is cleared. No other flags are affected.CLR bit:the content of directly addressed bit is cleared.SETB C: carry flag is set.SETB bit;CPL C;CPL bit;ANL C,bit;ANL C,/bit;ORL C,bit;ORL C,/bit;47. Define compare instructions.Microcontroller 8051 has four types of compare instructions. All compare instructions are three byte instructions. All are control jump instructions that means compare the two operands specified in the instruction, if their values are not equal, it will branch to the indicated address, otherwise proceed with next instruction.48. Give some examples for compare jump instructions. CJNE A,direct,rel; CJNE A,#data,rel; CJNE Rn,#data,rel; CJNE @Ri,#data,rel; 49. Write short notes on Rotate instruction with example. The A register can be rotated one bit position to the left or right with or without including carry flag in the rotation. If the carry bit is not included, then the rotation involves the 8 bits of the A register. If the carry flag is included, the 9 bits are involved in rotation .the SWAP instruction rotate the nibbles in A register. Ex: RL A; RR A; RLC A; RRC A; SWAP A;50. Define loop instruction.Loop instructions are used to execute a group of instructions ,a number of times as specified by a count value stored in any one of register or direct byte location.51. Define jump instruction.A jump instruction can replace the content of the program counter with a new program address number that causes the program execution to begin at the code located at the new address. In jump instructions, the control may be transferred within main program or within subroutine program.52.Classify types of jump instruction.The jump instructions are classified in to two types,

I. conditional jump

II.unconditional jump.53.Define unconditional jump instructions with example.This type of instruction does not depend on any specific condition.

Ex: AJMP addr11;

LJMP addr 16;

SJMP rel; JMP@A+DPTR.54.Define conditional jump instructions and classify their types.Conditional jumps perform a jump upon a specific condition .if the mentioned condition is true ,the control will jump to the target address, otherwise it will execute the instructions continuously. The destination will be within the 256 byte range (-128D to + 127D).Conditional jump instructions are two types ,

I.bit level,II.byte level logical instructions.55.Give some example for byte level unconditional jump instructions.JZ rel,JNZ rel,CJNE A,direct,rel,CJNE A,#data,rel,CJNE Rn,#data,rel,CJNE @Ri,#data,rel.56.Give some examples for bit level jump instructions.JC rel,JNC rel,JB bit,rel,JBC bit,rel,JNB bit,rel.57.Write short notes on CALL instruction Classify their types.The call instruction replaces the contents of the program counter with a new program address that causes the program execution to begin at the code located at the new address. During the execution of call instructions the control is transferred from main program to subroutine or from one subroutine to another subroutine.58.Define ACALL.ACALL address 11 (absolute call): ACALL is a two byte instruction .ACALL instruction is only used for handling subroutines. These instruction increments the programs counter twice. The subroutine called must therefore to start within the same 2k block of memory.59.Define LCALL.LCALL address 16 (long call): LCALL is a 3 byte instruction. The call instructions are generally used for handling subroutines and interrupts. These instructions increments program counter by 3. The subroutine may begin anywhere in the full 64K byte of memory address space.60. Classify the types of return instructions, write short note to each.There are 2 types of return instructions, they are RET, RETI.RET: The RET is a return from subroutine instruction.RETI: The RETI is a return from an interrupt service subroutine instruction.During the execution of both instructions, the high and low bytes of the pc are successively POP from the stack ,and decrementing the stack pointer by 2.61. DifferentiateRET and RETI instruction.The only difference between RET and RETI is that RETI tells the interrupt control system that the interrupt in progress is done. If there is no interrupt in progress at the time RETI is executed, then the RETI is functionally identical to RET.62. Write short notes on time delay routine.Delay routines are subroutines used for maintaining the timing of various operations in microcontroller. In control applications ,certain equipment is need to be ON/OFF after a specific time delay .In some applications ,certain operation has to be repeated after a specified time period .In such cases delay routines are used.63. How is internal RAM classified?The 128 bytes Internal RAM classified into, Register bank area, Bit and byte addressable area, Byte addressable area. 64. How many I/O ports placed in microcontroller 8051?

3 I/O ports. 65. How many SFRs are placed in microcontroller 8051.

21 special function 8 bit registers. Among them 11 Byte and bit addressable registers 10 Only byte addressable registers. 66. What is the purpose of SFRs? SFRs used to done some special functions in 8051, this registers are called special function registers. Eg.SCON,PCON etc.,67. What is the use of EA pin.D7D6D5D4D3D2D1D0

EAXXESET1EX1ET0EX0

EA-Disable all interrupts. If EA=0, no interrupts will be acknowledged. If EA=1, each interrupt source is individually disabled by its corresponding bit. 68. How is the internal RAM is classified. Register bank area (0-31) Bit and byte addressable locations (32-47) Only byte addressable locations (48-127) 69. Mention the three different address spaces of 8051. ROM (program memory) area. RAM (128 bytes data memory) area. Special function registers (upper 128 bytes of RAM) area. 70. How many register banks are placed in internal RAM? 4 Register banks (Bank 0, 1, 2, 3).71. How many bit addressable locations are placed in internal RAM? 128 bit addressable locations in internal RAM. (00-7F) 72. What is the use of carry flag? In an arithmetic operation when a carry is generated, the carry flag is set, otherwise reset. The carry flag also serves as a borrow flag for subtraction. 73. Where is the stack memory placed in 8051.

Stack may reside anywhere in the on-chip RAM memory area. 74. Which port is used for alternate input and output functions. Port 3.75. Define interrupt. Interrupts are control signals, used for getting immediate attention of microcontroller. When an interrupt occurs, the microcontroller stops the execution of main program and its control is immediately transferred to its corresponding service subroutine.76. Classify the types of interrupts, priority levels and their vector addresses in 8051. The microcontroller 8051 provides 5 interrupt sources. They are InterruptsPriority levelvector address

External interrupt 0 (IE0)Highest0003H

Timer interrupt 0 (TF0).000BH

External interrupt 1 (IE1).0013H

Timer interrupt 1 (TF1).001BH

Serial port interrupt (TI+RI).Lowest0023H

77. What are the signals are used to access the external data memory.

MOVX instructions are used to access the external data memory. 78. What is the use of PSEN signal? This pin is not activated for internal fetches. It is activated when the cpu is accessing external program memory. It is activated twice every machine cycle. 79. Explain MOV Rn, direct instruction. MOV Rn, direct-The content of directly addressed location is copied into register Rn.80. Explain JMP @A+DPTR instruction. JMP @A+DPTR-This instruction adds the 8-bit unsigned contents of the accumulator with the 16 bit data pointer, loads the resulting sum in the program counter. This will be address for subsequent instruction fetches. No flags are affected. 81. What is bit manipulation instruction?

The bit manipulation instructions perform data transfer, logical and branching operations only on bit operand.

Ex.MOV C,bit.UNIT II1. List the addressing modes of 8051. Immediate addressing mode. Direct addressing mode. Indirect addressing mode Register addressing mode. Index addressing mode. 2. Write the example for immediate addressing mode.

MOV A ,#64; this instruction loads the accumulator with the hexadecimal data of 64H.3. Write the example for register addressing mode.

MOV A, R3; This instruction moves the data from register R3 into accumulator.4. Write the example for direct addressing mode. MOV DIRECT,A;this instruction moves the content of accumulator to direct address directly. MOVA, DIRECT: This instruction copies the content of directly specified location to accumulator. 5. Writethe example for indirect addressing mode.

MOV @Ri,A;this instruction moves the content of ACC to the memory location specified by the register R1.6. Write example for index addressing mode.

MOVC A, @A+DPTR; the content of program memory ,which address is specified by the sum of the contents of the registers A and DPTR is moved into Accumulator.7. Define Assembler. An assembler is basically translator. It translates the assembly language program in to machine language program. 8.Classify the types of assembler. Manual assembler Macro assembler, Cross assembler, One pass assembler, Two pass assembler. 9. Define assembler directive. Assembler directives are some instructions in the assembly language program, which are not a part of processor instruction set. The assembler directives allow as to control the way in which a program assembles and lists. They will not create any executable machine language codes. The assembler directives also called pseudo operations.10. Give some examples for AD (Assembler directives). DB;EQU;END;Label;Comment. 11. Mention the different fields in assembly language instructions. An assembly language instructions consists of 4 fields, They are [Label:] mnemonic [operands] [; comment] Brackets indicate that a field is optional. 12. What is operand field? The operand field, if required, must follow the operation field, and must be preceded by at least one white space character. The operand field may contain a symbol, an expression or a combination of symbols and expressions separated by commas. 13. What are the fields used in assembly language instructions as optional. Label,operants,comment fields are optional in assembly language instructions.14. What are the instructions used to access the external RAM. MOVX A,@DPTR MOVX @DPTR, A, MOVX A,@Ri, MOVX@Ri,A. 15. How can you perform Multiplication with Example? MUL instruction performs an unsigned multiplication of the A register by the B register, and produces a double byte result .ACC receives the low order byte, and B receives the higher order byte. Ex:MUL AB The content of Accumulator is multiplied with the content of B register .After multiplication lower order result stored in Accumulator, higher order result is stored in B register. 16. What is the operation carried out when 8051 executes the instruction MOVC A,@A+DPTR ? The content of program memory which is addressed by the sum of DPTR and Accumulator is copied into Accumulator. UNIT III1. Classify types of timer/counter operating modes. Mode 0-13bit timer. Mode1-16 bit timer /counter. Mode 2-8 bit auto reload timer/counter. Mode 3-split timer. 2. Write TMOD register format. D7D6D5D4D3D2D1D0

GATEC/TM1M0GATEC/TM1M0

3. Write TCONregister format.

D7D6D5D4D3D2D1D0

TF1TR1TF0TR0IE1IT1IE0IT0

4. How many ports available in 8051.Microcontroller 8051 contains four I/O ports. They are port 0,port 1,port 2,port 3.5. Which port is called multifunctional I/O port. Port 3 is called as multifunctional I/O port. 6. Write alternate functions of port 3. Port pinsAlternate use

P3.0RXD serial data input

P3.1TXD serial data output

P3.2INT0 external interrupt 0

P3.3INT1 external input 1

P3.4T0 external timer 0 input

P3.5T1 external timer 1 input

P3.6WR external memory write pulse

P3.7RD external memory read pulse.

7. Specify byte addresses of 8051 I/O ports.

NAMEFUNCTIONBYTE ADDRESSBIT ADDRESSES

MSB LSB

P0input/outputport080H87H 80H

P1latch90H97H 90H

P2input/outputport1A0HA7H A0H

P3latch0B0HB7H B0H

input/outputport2

latch

input/outputport3

latch

8. How is internal RAM classified?The 128 bytes Internal RAM classified into, Register bank area,Bit and byte addressable area, Byte addressable area.9. Specify the address range of bit addressable locations of internal RAM area.The address range of bit addressable locations of internal RAM area is 00 7FH.10. What type of addressing is used for accessing bit addressable internal RAM.The bit addresses of internal RAM can be accessed only by using direct addressing.11. What will happen during the execution of MOV P2.0, C instruction? Moves the data placed in carry flag to port P2.0. 12. What are the registers used for timer/counter operations. TMOD timer/counter mode control register,TCON timer/counter control register.TH0,TL0TH1,TL113. What is the use of GATE bit in TMOD register? Timer/counter gating control .when GATE =1, timer/counter X is enabled only while INTX pin is high (hardware control) and TRX (in TCON register) is set. When GATE =0, TIMER/COUNTER X will run only while TRX =1 (software control). 14. How many bit addressable locations are placed in internal RAM? 128 bit addressable locations in internal RAM. (00-7F)15. Mention the SFRs used in Timer operation.

TMOD,TCON,TH0,TL0,TH1,TL1 16. What is the function of c/t bit in TMOD register?

C/T: countr/timer operation bit.

This Bit=0 Timer operation. Bit= 1 counter operation 17. State the function of M1, M0 bits in TMOD register. M1, M0 bits are mode selector bits. M1M0Operating modes

00Mode 0-13bit timer.

0 1 Mode 1-16 bit timer /counter. 1 0 Mode 2-8 bit auto reload timer/counter.

1 1 Mode 3-split timer. 18. What is the function of TF0 bit in TCON register? TF0-Timer 0 overflow flag bit. Set by hardware on timer/counter overflow. Cleared by hardware when processor vectors to its interrupt routine. 19. State the use of T0 pin of 8051.

T0-Timer/counter 0 external input pin.

UNIT IV1. Classify the types of serial port operating modes and their baud rates.ModesBaud rateMode 0-shift registers Fosc/12Mode 1-8 bit UART variableMode 2-9 bit UART Fosc/64 or Fosc/32Mode 3- 9 bit UART variable2. Classify the types of interrupts, priority levels and their vector addresses in 8051.

The microcontroller 8051 provides 5 interrupt sources. They areInterruptsPriority levelvector address

external interrupt 0 (IE0)highest0003H

timer interrupt 0 (TF0).000BH

external interrupt 1 (IE1).0013H

timer interrupt 1 (TF1).001BH

serial port interrupt (TI+RI).Lowest0023H

3. Write IE register format.D7D6D5D4D3D2D1D0

EAXXESET1EX1ET0EX0

4. Write IPregister format.

D7D6D5D4D3D2D1D0

XXXPSPT1PX1PT0PX0

5.Write SCON register format.

D7D6D5D4D3D2D1D0

SM0SM1SM2RENTB8RB8TIRI

6.Write PCON register format.

D7D6D5D4D3D2D1D0

SMOD------GF1GF0PDIDL

7. What is the difference between mode 2 and mode 3 in serial communication?Only one difference between mode 2 and mode 3 are mode 2 is fixed baud rate and mode 3 is variable baud rate.8. What are the registers used for serial communication in 8051. SCON serial port control register PCON power control register. 9. Specify the baud rate of serial communication in mode 2. The baud rate is programmable to either Fosc/32 or Fosc/64. 10. What is the use of RS 232? It is used for serial communication. It is a protocol standard as well as electrical standard. 11. Why drivers are used in between RS 232 and microcontroller. Line drivers are (voltage converter) used to convert RS232s signals to TTL voltage levels, that will be acceptable to the 8051s TXD and RXD pins.12. What are the SFR registers used in interrupt operations?The TCON, IP and IE special function registers are used for executing interrupts in microcontroller 8051.13. What are the different classifications of serial communication? i. synchronous data transfer, ii. asynchronous data transfer. 14. Write about synchronous and asynchronous data transfer. In synchronous data transfer a block of data is transferred at a time. In asynchronous data transfer only one byte of data transfer at a time.15. Specify some special IC chips used for serial communication.UART Universal asynchronous receiver transmitter.USART Universal synchronous - asynchronous receiver transmitter.16. Classify the types of serial communication based on direction of communication. i. simplex communication ii. half duplex communication iii. full duplex communication. 17. Define simplex, half duplex, full duplex communication. Simplex if the data transmission takes place only in one direction. Half duplex - if the data transmission is in one direction at a time.Full duplex if the data transmission takes place on both the direction at a time or simultaneously.18. Define protocol.The data to be transmitted are all 0s and 1s, it is difficult to find out where the byte of data starts and ends. Therefore, a set of rules called as protocol.19. Define framing.The start bit indicates the beginning of a byte and stop bit indicate the end of that byte. That is the actual data is placed in between start and stop bit. This procedure is called as framing.20. Define baud rate.The rate of data transfer is specified in terms of bits per second (bps).This rate is called as baud rate.21. Define band rate.The band rate is defined as the number of signal changes per second.22. What is the use of start and stop bit?To identify the beginning and end of a byte of data, we have add the start bit and stop bit with the byte of data to be transmitted.23. What is RS - 232? RS232C is a serial interface standard. It is developed by Electronic Industries Association (EIA).this standard describes the functions of 25 signals and handshake pins for serial data transfer. 24. What is MAX232? MAX 232 is a voltage converter. It converts from RS232 voltage levels to TTL voltage levels and viseversa.one advantage of MAX232 chip is that it uses +5v power supply. So a single power supply can be used to power both 8051 and MAX 232.25. What do you mean by software generated interrupt?If an interrupt lag is set 1 by the software program instruction, an interrupt is generated and executed in a similar way the hardware generated interrupts are handled. Since this generated by the software, it is called a software generated interrupt.26. Define interrupt handler.The program flow is always sequential. But the interrupts can stop the normal program flow, execute a subroutine and then resume the normal program flow. This subroutine called an interrupt handler.27. What is the use of IP, IE register in 8051?The programmer can control the interrupts by altering the control bits in the interrupt enable register (IE), and interrupt priority register (IP).28. How will you double the baud rate in 8051? The SMOD bit in special function register PCON is used to set the baud rate of serial communication. It is double baud rate bit. When this bit is set to 1, the baud rate is doubled, when the serial port is used in either mode 1, 2, 3. 29. What is the function of SMOD in PCON register? The SMOD bit in special function register PCON is used to set the baud rate of serial communication. It is double baud rate bit. When this bit is set to 1, the baud rate is doubled, when the serial port is used in either mode 1, 2, 3. 30. What is the function of REN bit in SCON register? REN- Enable serial reception. It is set /cleared by software to enable/disable reception. 31. How many timer/counters are placed in 8051? Microcontroller 8051 has two 16-bit timer/counter registers. They are timer 0 and timer 1. They are specified as two Register pairs (TH0, TL0) and (TH1, TL1). 32. Define 8051 timer functions. In the timer function, the register is incremented every machine cycle. That means in timer operation it counts the machine cycles. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of oscillator frequency. 33. Define 8051 counter functions. The counter is programmed to count the external clock pulses, and then it is known a counter. In the counter function, the register is incremented in response to 1 to 0 transitions at its corresponding external input pin T0 or T1. Since it takes at least 2 machine cycles (24 oscillator periods) to recognize a 1 to transition. The maximum count rate is 1/24 of the oscillator frequency (fosc/24). 34. What is the difference between mode 2 and mode 3 of serial communication? Mode 2 & 3 are used for same operation but baud rate is varied. Mode2 9 bit UART (fixed baud rate) Mode 3 9 bit UART (Variable baud rate) 35. How is the serial transmission is initiated in 8051?. The transmission is initiated by any instruction that uses SBUF as a destination register. Ex.MOV SBUF, A36. What are the conditions required for initiating a serial reception. Reception is initiated in Mode 0 by the condition RI = 0 and REN = 1. In other modes it is initiated by the incoming start bit, if REN = 1. 37. What are the registers used for serial communication.

SCON, PCON, TMOD, TH1, TL1, TH0, TL0, SBUF. 38. Specify the baud rate of serial communication in mode 2. The baud rate in Mode 2 depends on the value of SMOD in special function register in PCON. If SMOD = 0, the baud rate is fosc/64. If SMOD = 1, the baud rate is fosc/32. Mode 2 baud rate = 2SMOD X (oscillator frequency)6439. What is interrupt signal? Interrupts are control signals, used for getting immediate attention of microcontroller. When an interrupt occurs, the microcontroller stops the execution of main program and its control is immediately transferred to its corresponding service subroutine. 40. What are the SFRs used in interrupt operations. IE, IP, SCON, TCON.UNIT V1. Define peripheral. The microcontroller accepts data from input devices (keyboard, switches) then it processes the data as per the instructions received from the memory unit. After processing the data, it sends the result to the output devices (LED display, LCD, printers). These input and output devices are called peripherals. 2. Define interfacing. Designing logic circuits and writing instructions to enable the microcontroller/microprocessor to communicate with these peripherals is called interfacing.3. What is the use of 8255?8255 is a programmable peripheral interface. It is used to perform a variety of input/output functions in a microcomputer system. The 8255 interfaces the microprocessor/microcontroller on one side with peripherals on the other side.4. Mention the ports placed in 8255.The 8255 consists of two 8 bit ports of port A and port B, and two 4 bit ports of port C upper and port C lower. The ports are grouped as Group A and Group B.Group A consists of port A (PA0 PA7) and port C upper (PC7 PC4).Group B consists of port B (PB7 PB0) and port C lower (PC3 PC0).5. Define control word.The control section of 8255 has an 8 bit register called control register. An 8 bit binary word present in the control register is called control word.6. State the modes of operation of 8255.The operation of 8255 can be classified into two modes. They are Bit set/Reset mode and I/O mode.7. How is the I/O mode of 8255 classified?The I/O mode is further classified into 3 modes. They are Mode 0 - simple I/O portMode 1 Strobe I/O port (hand shake I/O port) Mode 2 Bidirectional I/O port.8. What is relay?A relay is an electrically controllable switch widely used in industrial controls, automobiles and appliances. It allows the isolation of two separate sections of a system with two different voltage sources.9. Mention the 3 important components of electromagnetic relay.The electromagnetic relays have 3 components: coil, spring and contacts. 10. Define opto isolator.Opto isolator is otherwise called opto coupler. It isolates two part of a system. 11. Define transducers (sensors).Transducers convert physical data such as temperature, light intensity, flow and speed to electrical signals. Depending on the transducers, the output maybe in the form of voltage, current, resistance or capacitance.12. How is the output voltage of LM 34 varied?The sensors of LM 34 series are precision integrated circuit temperature sensors whose output voltage is linearly proportional to the Fahrenheit temperature. Its output is varied to 10mV for each degree of Fahrenheit temperature.13. How is the output voltage of LM 35 varied?LM 35 series sensors are precision integrated circuit temperature sensors, whose output voltage is linearly proportional to the Celsius temperature. Its output is varied to 10mV for each degree of centigrade temperature.14. What is signal conditioning?Signal conditioning is widely used for data acquisition. The most common transducers produce an output in the form of voltage, current, charge, capacitance and resistance. These signals are converted into voltage, in order to send input to an A to D converter. This conversion is commonly called signal conditioning.15. Define ADC.Analog to digital converters are most widely used devices for data acquisition. Digital computers use binary values, but in the physical world everything is analog.ADC is used to convert these analog values into digital.16. Mention the ports placed in group A and group B of 8255. Group A-port A and port C upper (PC7-PC4). Group B-port B and port C lower (PC3-PC0). 17. Which technique is used in ADC 0808.Successive approximation technique is used in ADC 0808. 18. What is the use of MAX 1112 ADC chip?MAX 1112 ADC chip is used for serial analog to digital conversion.19. Define DAC.DAC digital to analog converter. It is used to convert digital signals to analog signals. In DAC the number of input data bits decides the resolution. An n bit DAC provides 2n discrete voltage (or current) levels.20. State the output current of DAC 0808.I out=I ref (D7/2+D6/4+D5/8+D4/16+D3/32+D2/64+D1/128+D0/256). I ref is the input current; D0 is LSB, D7 is MSB, I out is output current.21. Mention three major tasks of keyboard to get a meaningful data. Sense a key actuation, Debounce the key, Decode the key. 22. Mention the different types of seven segment LEDs. Common anode type Common cathode type. 23. Mention the two important registers placed in LCD. There are two important registers of Data register, Command register placed inside the LCD.24. Specify some important LCD module.They are available in 162, 201, 202, 204, and 402 sizes. The first digit represents number of characters in each line. Second digit represents number of lines.ex:162 means, 16 characters per line and 2 lines.25. What is the use of stepper motor?Stepper motor is a device, used for getting accurate position control of rotating shafts. It converts electrical pulses into mechanical movements. A stepper motor employs rotation of its shaft, in terms of steps rather than continues rotation, as in the case of AC or DC motors.26. Which technique is used for varying the speed of DC motors used in microcontrollers?PWM pulse width modulation technique is used for varying the speed of DC motors in microcontrollers.27. What is the use of RTC?The real time clock (RTC) is a widely used device that provides accurate time and date for many applications. The RTC chip in IBMPC provides time components of hour, minute, and second, in addition to the date/calendar components of year, month and day. It uses an internal battery, which keeps the time and date even when the power is off.28. Mention the capacity of nonvolatile RAM placed inside of DS 12887.The DS 12887 has a total of 128 bytes of nonvolatile RAM. It uses 14 bytes of RAM for clock/calendar and control registers, and the other 114 bytes of RAM for general purpose data storage.29. What is key bounce?One of the most common problems with a single switch is keybounce.key bounce refers to the fact that when the contacts of a mechanical switch is closed, they bounce for a short time before staying together.30. Define conversion time of ADC.The conversion time of ADC is defined as the time it takes the ADC to convert the analog input to digital number.31. What is the use of IC 8253? IC 8253 is a programmable counter /timer It generate accurate time delays It can be used for applications such as real time clock, an event counter, square wave generator. 32. Which mode of IC 8253 is called as software triggered strobe? Mode 4 33. List the operating modes of IC 8253. Mode 0 (interrupt on terminal count) Mode 1 (programmable monoshot) Mode 2 (rate generator) Mode 3 (square wave generator) Mode 4 (software triggered strobe) Mode 5 (hardware triggered strobe) 34. How many counters placed in 8253? 3 counters (16 bit presettable down counters)