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Anna University , Chennai
Department of B.E-Electrical and Electronics Engineering
Fifth Semester
EE6502 Microprocessors and Micro Controllers
Important 2 Marks with Answers - Unitwise
(Regulation 2013)
QUESTION BANK
EE 6502 / Microprocessor and Microcontroller
UNIT – IV: PERIPHERAL INTERFACING
PART A
1. What are the different ways to end the interrupt execution in 8259 PIC? (A/M’11)
AEOI (Automatic End of Interrupt) mode the ISR bit is reset at the end of the second INTA
pulse. Otherwise, the ISR bit remains set until the issue of an appropriate EOI command at the
end of the interrupt subroutine.
2. What is the function of Scan section in 8279 programmable keyboard/Display controller?
(A/M’11)
Scan section which has two modes (i) Encoded Mode (ii) Decoded Mode
Encoded Mode: In this mode, Scan counter provides a binary count from 0000 to 1111 the four
scan lines (SC3 – SC0) with active high outputs.
Decoded Mode: The internal decoder decodes the least significant 2 bits of binary count and
provides four possible combinations on the scan lines (SC3- SC0) : 1110,1101,1011 and 0111.
3. Draw the ‘mode word’ format of 8251 USART. (N/D’11) (N/D’12)
4. State the use of ISR and PR registers in 8259 PIC. (N/D’11)
ISR- Interrupt service Register Stores all the levels that are currently being serviced.
PR– Priority Resolver determines the priorities of the bits set in the IRR (Interrupt Request
register). The bit corresponding to the highest priority interrupt input is set in the ISR during the
INTA input.
5. What are the salient features of INTEL 8259 Programmable interrupt controller? M/J 14
1. It manage eight Priority interrupt request.
2. The interrupt vector addresses are programmable.
3. The8259 are programmed to accept either the level triggered or edge triggered Interrupt request.
4. The interrupt can be masked or unmasked individually.
5. 8259 helps to get the information of pending interrupts, in-service interrupts and
masked interrupts
6. How data is transmitted in asynchronous serial communication? M/J ‘14
Data is transmitted by setting transmission enable bit in the command instruction.
When transmitter is enabled and CTS =0 the transmitter is ready to transfer data on Tx D line.
The data bits is framed with one start bit and stop bits and then transmitted.
7. What are the applications of D/A converter interfacing with 8255? M/J ‘12
Generating square, triangular and sine waveform, used in automatic process control
8. What is keyboard interfacing? M/J 12
Keyboard interfacing is interfacing an input device. Push button switches are used.in simple
keyboard interface one input line is required to interface one key and this number will increase
with number of keys. It is in the form of matrix with rows and columns and at the intersection a
switch is present.
9. What are the different peripheral interfacing used with 8085 processor? M/J 13
8255PPI, 8279 Keyboard and display controller, 8251 USART, 8259 PIC and 8254 - timer
10. What are the output terminals in USART 8251? M/ J 13
RD, WR
11. What is the need for 8259 PIC?
It is necessary to solve multiple interrupt requests (more than five) we use an external
device called a PIC. It is possible to increase the interrupt handling capacity of the
microprocessor. When executing an interrupt an ISR can be serviced.
12. What are the basic modes of 8255? N/D 2013
1. BSR mode
2. I/O mode which is operated in mode 0, mode 1 and mode 2
13. What are the operating modes of IC 8253 / 8254 Timer?
There are 6 operating modes in IC 8254 Timer they are
Mode 0: Interrupt on Terminal Count
Mode 1: Hardware – Triggered one shot
Mode 2 – Rate Generator
Mode 3 – Square wave generator
Mode 4 – Software triggered strobe
Mode 5- Hardware triggered strobe
14. What is key de bouncing?
The push button keys when pressed, bounces a few times, closing and opening the contact before
providing a steady reading. The reading taken during the bouncing period may be wrong.
Therefore, microprocessor must wait until the key reach to a steady state known as key
debounce.
15. What is the difference between A/D and D/A converters?
Digital-to-analog is used to get a proportional analog voltage or current for the digital data given
out by the microprocessor. An ADC converts the input analog voltage levels to the
corresponding discrete digital signals.
16. Define the following terms for D/A converters.
i) Resolution: Resolution of a converter determines the degree of accuracy in conversion.It is
equal to 1/2n.
ii) Accuracy: Accuracy is the degree to which information on a map or in a digital database
matches true or accepted values. Accuracy is an issue pertaining to the quality of data and the
number of errors contained in a dataset or map.
iii) Monotonicity : If a clock has monotonicity, then each successive time reading from that clock
will yield a time further in the future than the previous reading.
iv) Conversion time: The time required by an analog to digital converter to fully convert and
analog input sample.
17. List the features of 8279.
(i) It has built in hardware to provide key debounce.
(ii) It provides two output modes for display interface : Left and Right entry
(iii) It provides three input modes for keyboard interface: Scanned keyboard Mode, Scanned
sensor matrix mode and strobed input mode.
(iv) It provides multiplexed display interface with blanking and inhibit options.
18. How is DMA initiated?
When the IO device needs a DMA transfer, it will send DMA request signal to the DMA
controller. The DMA controller in turn sends a HOLD request to the processor. When the
processor receives a HOLD request, it will drive its tristated pins to high impedance state at the
end for current instruction execution and send an acknowledge signal to the DMA controller.
Now the DMA controller will perform DMA transfer
19. What are the different types of DMA?
Cycle stealing (or Single transfer) DMA, Block transfer (or Burst Mode)DMA and Demand
transfer DMA.
20. What is Cycle stealing DMA?
In Cycle stealing DMA, the DMA controller will perform one DMA transfer in between
instruction cycles (i.e. in this mode, the execution of one processor instruction and one DMA
data transfer will take place alternatively).
21. What is the function of the GATE signal in timer 8254?
In timer 8254, the GATE signal acts as a control signal to start, stop or maintain the
counting process. In modes 0, 2, 3, and 4 the GATE signal should remain high to start and
maintain the counting process. In modes 1 and 5, GATE signal has to make low to high
transitions to start the counting process and need not remain high to maintain the counting
process.
22. What is meant by Baud rate?
The rate at which the serial data is being transferred is called Baud rate.
23. What is meant by doubling the baud rate in the 8051?
We can double the baud rate in 8051 using two ways
i) By doubling the crystal frequency.
ii) By making SMOD bit in the PCON register from 0 to 1.
24. What is the function of C/T bit in TMOD register in timer in 8051?
C/T bit in the TMOD register decides the timer/counter functioning as a counter or a timer.
When C/T = 0, the timer mode is selected and the crystal is used as a source of frequency.
When C/T =1, the counter mode is selected, it gets its pulse from outside the 8051. The counter
counts up for each clock pulse applied at the pins of port 3
25. What is meant by Handshake signals in 8255 PPI?
The MPU and peripherals operates at different speed; signals are exchanged prior to data transfer
between the fast responding MPU and slow responding peripherals such as printer and data
converters. These signals are called Handshake signals.
26. What is meant by Over Run error (OE), Parity error (PE) and framing error (FE) in 8251
PCI?
Over Run Error: The OE flag is set when the CPU does not read a character before the next one
becomes available. It is reset by the Error reset (ER) bit in the command instruction. OE does not
inhibit operation of the 8251. However the previously over run character is lost.
Parity Error (PE): The PE flag is set when a parity error is detected. It is reset by the ER bit of
the command instruction. PE does not inhibit operation of the 8251.
Framing Error: The FE flag is set when a valid stop bit is not detected at the end of every
character. It is reset by the ER bit of the command instruction. FE does not inhibit the operation
of the 8251.
27. How does a serial communication classified?
The serial communication are classified according to the direction and data flow as
Simplex transmission- data transmitted in only one direction, eg – transmission from a
microcomputer to a printer.
Duplex Transmission – data flows in both direction. If data gets transmitted one way at a time
called as half duplex and if data gets transmitted in both direction called as full duplex. Eg
transmission between two computers, between a computer and a terminal.
28. What are the types of priority modes in 8259 PIC?
Fully Nested Mode, Automatic rotation mode, specific rotation mode and end of Interrupt.
29. What is meant by two key lockout and N key roll over in 8279?
The keys are automatically de bounced and the keyboard can operate in two modes:
i) Two key Lock out – In this mode if two keys are pressed almost simultaneously, only the
first key is recognized.
ii) N key roll over- In this mode simultaneous keys are recognized and their codes are stored
in the internal buffer; it can also be set up so that no key is recognized until one key remains
pressed.
30. Explain the mode3 of 8051 serial ports? (Nov-2009)
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
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.
31. List the operating modes of 8255A PPI?
(i) Two 8-bit ports (A and B)
(ii) Two 4-bit ports (Cu and CL)
(iii) Data bus buffer
(iv) Control logic
32. Compare between Synchronous and Asynchronous Data transmission?
S.NO Synchronous Data Transmission Asynchronous Data transmission
1 In this transmission, both transmitter
and receiver are synchronous with the
common CLK signals
In this transmission, both transmitter and
receiver are not synchronous with the
common clock (CLK), they use separate clock
signals
2 In this mode, the framing bits are sent
along with block ( at the beginning of
block)
Framing bits are sent along with each
character ( at the beginning and end of the
character)
3 The speed of the synchronous data
transmission is higher than 20K bauds
The speed of the asynchronous data
transmission is less than 20K bauds.
4 Framing information is SIM character Framing information is start and stop bits
5 It is always implemented through
hardware
It is implemented through software
PART - B
1. With neat block diagram explain 8255 PPI. .(M/J 2013)
2. i) Using model, write a program to communicate between two microprocessors using 8255.
ii) Show the control word format of 8255 and explain how each bit is programmed.
3. With neat block diagram explain the functions of 8259. (M/J 2013)
4. i) Bring about the features of 8251.ii) Discuss how 8251 is used for serial communication of
data.M/J2013
5. Explain the functional block diagram of 8279. (M/J 2013)
6. Explain the operation of 8255 PPI port A programmed as input and output in mode 1 with
necessary handshaking signals. (A/M’11).
7. Show and explain the ADC interfacing with 8085 microprocessor. (A/M’11)
8. With functional diagram, explain the operation and programming of 8251 USART in detail.
(A/M’11) (M/J 12)
9. Explain the operating modes of 8255 PPI interface. (N/D’11)
10. Draw the logical block diagram of 8279 keyboard display controller and explain.
(N/D’11)M/J 13
11. Draw the control word of 8253 timer/counter and explain the operating modes of 8253
timer/counter. (N/D’11)
12. Why do we need ADC and DAC? Draw the block diagram to interface 8085 microprocessor
with ADC and DAC. (N/D’11) (M/J 12)
13. Describe the comparison of I/O mapped and memory mapped I/O interfacing. (M/J 12)
14. Draw and explain the functional block diagram of 8259 PIC. (M/J 12)
15. Draw and explain the functional block diagram of 8237.
16. Draw and explain the functional block diagram of 8255 PPI with 8051
17. Draw and explain the functional block diagram of 8259 PIC with 8051
18. Draw and explain the functional block diagram of 8254 timer with 8051
19. Draw and explain the functional block diagram of 8279 with 8051
20. Draw and explain the functional block diagram of 8251 with 8051
21. Draw the block diagram to interface 8051 microprocessor with ADC and DAC
UNIT – V: MICRO CONTROLLER PROGRAMMING & APPLICATIONS
PART – A
1. List the different types of 8051 instructions. ( April/may -2010, Nov/Dec-2011)
The different types of 8051 instructions are:
a. Logical Instructions
b. Arithmetic Instructions
c. Data transfer Instructions
d. Branch Instructions
e. Jump & CALL Instruction
2. What are the various operations performed by Boolean variable instructions of 8051?(
April/may -2010, April/may -2011)
Boolean variable instructions perform the following operations
BOOLEAN OPERATOR MNEMONICS
AND(AND logical) ANL
OR(OR logical) ORL
NOT(COMPLEMENT) CPL
XOR(Exclusive OR logical) XRL
3. What is the operation of the given 8051 microcontroller instructions:
XRL A, direct? (April/may -2011)
XOR each bit of A with the same bit of the direct RAM address and the result is stored in A
(Acc).
4. Draw the flow chart for the programming of serial port of 8051 (May/June -2012)
5. What are the applications of 8051 microcontroller? (May/June -2012)
The applications of 8051 microcontroller are:
• Automobile
• Aeronautics
• Mobile communication
• Robotics
• Remote sensing etc.,
6. How is the pulse generated from microcontroller for stepper motor control (May/June -
2013)
To cause the stepper to rotate, we have to send a pulse to each coil in turn. The 8051 does not
have sufficient drive capability on its output to drive each coil, so there are a number of ways to
drive a stepper, Stepper motors are usually controlled by transistor or driver IC like ULN2003.
Driving current for each coil is then needed about 60mA at +5V supply.
7. State the functions performed by the instructions JBC and CJNE in 8051 microcontroller.
(May/June -2014)
•
to the status of carry flag or any bit addressable locations
•
8. Why do we need opto-isolator circuit between microcontroller and the stepper motor?
(Nov/Dec-2011)
Opto-isolator are widely used to isolate the stepper motor’s EMF voltage and keep it
form damaging the digital microcontroller system.
9. Why interfacing is needed for 1/0 devices? (Nov-2009])
Generally I/O devices are slow devices. Therefore the speed of I/O devices does not match with
the speed of microprocessor. And so an interface is provided between system bus and I/O
devices.
10. What is the operation carried out when 8051 executes the instruction MOVC A, @ A +
DPTR? (Nov-2007)
This instruction loads the accumulator from the contents of program memory whose address is
given by the sum of the contents of accumulator and contents of DPTR register (A) ‹— ((A) +
(DPTR))
11. Write program to load accumulator, DPH, &DPL using 8051? (Nov-2007)
MOV A,#30
MOV DPH, A
MOV DPL, A
12. Write a program to perform multiplication of 2 numbers using 8051? (NOV-2009)
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
13. Write a program to mask the 0th &7th bit using 8051? (APRIL-2009)
MOV A,#data
ANL A,#81
MOV DPTR,#4500
MOVX @DPTR,A
LOOP SJMP LOOP
14. 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
15. Explain PUSH and POP instructions in 8051.
PUSH-The stack pointer is incremented by one. The contents of the indicated variable is
then copied into the internal RAM location addressed by the stack pointer.
POP-Reverse of PUSH operation.
16. How many ports are bit addressable in an 8051 microcontroller?(N/D ‘12’)
In 8051 there are many bit-addressable registers such as A (ACC), B, SCON,
PCON, TCON, p0, p1, p2, p3.
17. Write a program to find the 2’s complement using 8051?( NOV-2008)
MOV A, R0
CPL A
INC A
18. Explain rotate instructions of 8051.
RL A,
RLC A,
RR A,
RRC A
19. Explain DAA instruction of 8051.
Decimal adjust accumulator for addition bytes
20. What does the mnemonics “LCALL” and “ACALL” stands for? (Nov/Dec-2012)
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.
21. What are the use of PWM in motor control using microcontroller?
The speed of the dc motor depends on the applied voltage. The average applied dc
voltage and power can be varied using a technique called pulse width modulation. In this
technique the dc power supply is not a voltage of fixed amplitude ie it is a pulsating DC
voltage. By changing the pulse width we can change the applied power.
22. Calculate the reload value of timer1 for achieving a baud rate of 4800in 8051 for a crystal
frequency of 11.0592MHz?
TH = 256 – k * Oscillatory frequency
-------------------------------
384 * Baud rate
= 256 – 1*11.0592*10E6 / 384*4800
= 250 = FAH
23. List the features of ADC0804?
i) 8-bit successive approximation ADC
ii) Access time is 135ns
iii) Conversion time is 100µs
iv) It has an on chip clock generator
v) It does not require any zero adjustment
vi) It operates on single 5V power supply.
24. What is the output of the program?
MOV R0, A
XRL A, # 3F H
XRL A, R0
The contents of A register will be 3F H and the contents of R0 will be the initial contents
of A
25. What are the different addressing modes of microcontroller 8051? ( A/ M -2008)
i) Register addressing
ii) Direct byte addressing
iii) Register indirect addressing
iv) Immediate addressing
v) Register specific
vi) Index
26. Give the PSW setting for making register bank 2 as default register bank in 8051
microcontroller ( M / J 2007)
MOV PSW, #10 ; SELECT BANK 2
MOV A, R0 ; (A) ‹— (R0) FROM BANK 2
MOV PSW, #00 ; SELECT BANK 0
CLR C ; CLEAR CARRY
SUBB A, R1 ; A ‹— A- (R1) FROM BANK 0
The above program is to subtract the contents of R1 of BANK0 from the contents of RO
of Bank 2.
PART - B
1. Draw the schematic for interfacing a stepper motor with 8051 microcontroller and write
8051 ALP for changing speed and direction of motor. (M/J 12)
2. Explain the data transfer instructions and program control instructions of 8051
microcontroller (A/M’11)
3. Write an assembly language program based on 8051 microcontroller instruction set to
perform four arithmetic operations on 2, 8 bit data. (A/M’11)
4. Explain the interfacing of Keyboard/Display with 8051 microcontroller. (A/M’11)
5. Explain the servomotor control using 8051 microcontroller. (A/M’11)
6. Explain with a program to rotate the stepper motor in both clockwise and anticlockwise
direction using 8051 microcontroller. (N/D’11)
7. How to interface a 7 segment display using 8051 microcontroller. (N/D’11)
8. How 8051 is used in washing machine control. (N/D’11) (M/J 12)
9. How do you interface a 4X4 matrix keyboard using 8051 microcontroller. (N/D’11)
10. Write short notes on LCD interface. [May-2009]
11. Explain the hardware and software program to interface 8051 with washing machine?
Anna University , Chennai
Department of B.E-Electrical and Electronics Engineering
Fifth Semester
EE6502 Microprocessors and Micro Controllers
Important 2 Marks with Answers - Unitwise
(Regulation 2013)
QUESTION BANK
EE 6502 / Microprocessor and Microcontroller
UNIT – IV: PERIPHERAL INTERFACING
PART A
1. What are the different ways to end the interrupt execution in 8259 PIC? (A/M’11)
AEOI (Automatic End of Interrupt) mode the ISR bit is reset at the end of the second INTA
pulse. Otherwise, the ISR bit remains set until the issue of an appropriate EOI command at the
end of the interrupt subroutine.
2. What is the function of Scan section in 8279 programmable keyboard/Display controller?
(A/M’11)
Scan section which has two modes (i) Encoded Mode (ii) Decoded Mode
Encoded Mode: In this mode, Scan counter provides a binary count from 0000 to 1111 the four
scan lines (SC3 – SC0) with active high outputs.
Decoded Mode: The internal decoder decodes the least significant 2 bits of binary count and
provides four possible combinations on the scan lines (SC3- SC0) : 1110,1101,1011 and 0111.
3. Draw the ‘mode word’ format of 8251 USART. (N/D’11) (N/D’12)
4. State the use of ISR and PR registers in 8259 PIC. (N/D’11)
ISR- Interrupt service Register Stores all the levels that are currently being serviced.
PR– Priority Resolver determines the priorities of the bits set in the IRR (Interrupt Request
register). The bit corresponding to the highest priority interrupt input is set in the ISR during the
INTA input.
5. What are the salient features of INTEL 8259 Programmable interrupt controller? M/J 14
1. It manage eight Priority interrupt request.
2. The interrupt vector addresses are programmable.
3. The8259 are programmed to accept either the level triggered or edge triggered Interrupt request.
4. The interrupt can be masked or unmasked individually.
5. 8259 helps to get the information of pending interrupts, in-service interrupts and
masked interrupts
6. How data is transmitted in asynchronous serial communication? M/J ‘14
Data is transmitted by setting transmission enable bit in the command instruction.
When transmitter is enabled and CTS =0 the transmitter is ready to transfer data on Tx D line.
The data bits is framed with one start bit and stop bits and then transmitted.
7. What are the applications of D/A converter interfacing with 8255? M/J ‘12
Generating square, triangular and sine waveform, used in automatic process control
8. What is keyboard interfacing? M/J 12
Keyboard interfacing is interfacing an input device. Push button switches are used.in simple
keyboard interface one input line is required to interface one key and this number will increase
with number of keys. It is in the form of matrix with rows and columns and at the intersection a
switch is present.
9. What are the different peripheral interfacing used with 8085 processor? M/J 13
8255PPI, 8279 Keyboard and display controller, 8251 USART, 8259 PIC and 8254 - timer
10. What are the output terminals in USART 8251? M/ J 13
RD, WR
11. What is the need for 8259 PIC?
It is necessary to solve multiple interrupt requests (more than five) we use an external
device called a PIC. It is possible to increase the interrupt handling capacity of the
microprocessor. When executing an interrupt an ISR can be serviced.
12. What are the basic modes of 8255? N/D 2013
1. BSR mode
2. I/O mode which is operated in mode 0, mode 1 and mode 2
13. What are the operating modes of IC 8253 / 8254 Timer?
There are 6 operating modes in IC 8254 Timer they are
Mode 0: Interrupt on Terminal Count
Mode 1: Hardware – Triggered one shot
Mode 2 – Rate Generator
Mode 3 – Square wave generator
Mode 4 – Software triggered strobe
Mode 5- Hardware triggered strobe
14. What is key de bouncing?
The push button keys when pressed, bounces a few times, closing and opening the contact before
providing a steady reading. The reading taken during the bouncing period may be wrong.
Therefore, microprocessor must wait until the key reach to a steady state known as key
debounce.
15. What is the difference between A/D and D/A converters?
Digital-to-analog is used to get a proportional analog voltage or current for the digital data given
out by the microprocessor. An ADC converts the input analog voltage levels to the
corresponding discrete digital signals.
16. Define the following terms for D/A converters.
i) Resolution: Resolution of a converter determines the degree of accuracy in conversion.It is
equal to 1/2n.
ii) Accuracy: Accuracy is the degree to which information on a map or in a digital database
matches true or accepted values. Accuracy is an issue pertaining to the quality of data and the
number of errors contained in a dataset or map.
iii) Monotonicity : If a clock has monotonicity, then each successive time reading from that clock
will yield a time further in the future than the previous reading.
iv) Conversion time: The time required by an analog to digital converter to fully convert and
analog input sample.
17. List the features of 8279.
(i) It has built in hardware to provide key debounce.
(ii) It provides two output modes for display interface : Left and Right entry
(iii) It provides three input modes for keyboard interface: Scanned keyboard Mode, Scanned
sensor matrix mode and strobed input mode.
(iv) It provides multiplexed display interface with blanking and inhibit options.
18. How is DMA initiated?
When the IO device needs a DMA transfer, it will send DMA request signal to the DMA
controller. The DMA controller in turn sends a HOLD request to the processor. When the
processor receives a HOLD request, it will drive its tristated pins to high impedance state at the
end for current instruction execution and send an acknowledge signal to the DMA controller.
Now the DMA controller will perform DMA transfer
19. What are the different types of DMA?
Cycle stealing (or Single transfer) DMA, Block transfer (or Burst Mode)DMA and Demand
transfer DMA.
20. What is Cycle stealing DMA?
In Cycle stealing DMA, the DMA controller will perform one DMA transfer in between
instruction cycles (i.e. in this mode, the execution of one processor instruction and one DMA
data transfer will take place alternatively).
21. What is the function of the GATE signal in timer 8254?
In timer 8254, the GATE signal acts as a control signal to start, stop or maintain the
counting process. In modes 0, 2, 3, and 4 the GATE signal should remain high to start and
maintain the counting process. In modes 1 and 5, GATE signal has to make low to high
transitions to start the counting process and need not remain high to maintain the counting
process.
22. What is meant by Baud rate?
The rate at which the serial data is being transferred is called Baud rate.
23. What is meant by doubling the baud rate in the 8051?
We can double the baud rate in 8051 using two ways
i) By doubling the crystal frequency.
ii) By making SMOD bit in the PCON register from 0 to 1.
24. What is the function of C/T bit in TMOD register in timer in 8051?
C/T bit in the TMOD register decides the timer/counter functioning as a counter or a timer.
When C/T = 0, the timer mode is selected and the crystal is used as a source of frequency.
When C/T =1, the counter mode is selected, it gets its pulse from outside the 8051. The counter
counts up for each clock pulse applied at the pins of port 3
25. What is meant by Handshake signals in 8255 PPI?
The MPU and peripherals operates at different speed; signals are exchanged prior to data transfer
between the fast responding MPU and slow responding peripherals such as printer and data
converters. These signals are called Handshake signals.
26. What is meant by Over Run error (OE), Parity error (PE) and framing error (FE) in 8251
PCI?
Over Run Error: The OE flag is set when the CPU does not read a character before the next one
becomes available. It is reset by the Error reset (ER) bit in the command instruction. OE does not
inhibit operation of the 8251. However the previously over run character is lost.
Parity Error (PE): The PE flag is set when a parity error is detected. It is reset by the ER bit of
the command instruction. PE does not inhibit operation of the 8251.
Framing Error: The FE flag is set when a valid stop bit is not detected at the end of every
character. It is reset by the ER bit of the command instruction. FE does not inhibit the operation
of the 8251.
27. How does a serial communication classified?
The serial communication are classified according to the direction and data flow as
Simplex transmission- data transmitted in only one direction, eg – transmission from a
microcomputer to a printer.
Duplex Transmission – data flows in both direction. If data gets transmitted one way at a time
called as half duplex and if data gets transmitted in both direction called as full duplex. Eg
transmission between two computers, between a computer and a terminal.
28. What are the types of priority modes in 8259 PIC?
Fully Nested Mode, Automatic rotation mode, specific rotation mode and end of Interrupt.
29. What is meant by two key lockout and N key roll over in 8279?
The keys are automatically de bounced and the keyboard can operate in two modes:
i) Two key Lock out – In this mode if two keys are pressed almost simultaneously, only the
first key is recognized.
ii) N key roll over- In this mode simultaneous keys are recognized and their codes are stored
in the internal buffer; it can also be set up so that no key is recognized until one key remains
pressed.
30. Explain the mode3 of 8051 serial ports? (Nov-2009)
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
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.
31. List the operating modes of 8255A PPI?
(i) Two 8-bit ports (A and B)
(ii) Two 4-bit ports (Cu and CL)
(iii) Data bus buffer
(iv) Control logic
32. Compare between Synchronous and Asynchronous Data transmission?
S.NO Synchronous Data Transmission Asynchronous Data transmission
1 In this transmission, both transmitter
and receiver are synchronous with the
common CLK signals
In this transmission, both transmitter and
receiver are not synchronous with the
common clock (CLK), they use separate clock
signals
2 In this mode, the framing bits are sent
along with block ( at the beginning of
block)
Framing bits are sent along with each
character ( at the beginning and end of the
character)
3 The speed of the synchronous data
transmission is higher than 20K bauds
The speed of the asynchronous data
transmission is less than 20K bauds.
4 Framing information is SIM character Framing information is start and stop bits
5 It is always implemented through
hardware
It is implemented through software
PART - B
1. With neat block diagram explain 8255 PPI. .(M/J 2013)
2. i) Using model, write a program to communicate between two microprocessors using 8255.
ii) Show the control word format of 8255 and explain how each bit is programmed.
3. With neat block diagram explain the functions of 8259. (M/J 2013)
4. i) Bring about the features of 8251.ii) Discuss how 8251 is used for serial communication of
data.M/J2013
5. Explain the functional block diagram of 8279. (M/J 2013)
6. Explain the operation of 8255 PPI port A programmed as input and output in mode 1 with
necessary handshaking signals. (A/M’11).
7. Show and explain the ADC interfacing with 8085 microprocessor. (A/M’11)
8. With functional diagram, explain the operation and programming of 8251 USART in detail.
(A/M’11) (M/J 12)
9. Explain the operating modes of 8255 PPI interface. (N/D’11)
10. Draw the logical block diagram of 8279 keyboard display controller and explain.
(N/D’11)M/J 13
11. Draw the control word of 8253 timer/counter and explain the operating modes of 8253
timer/counter. (N/D’11)
12. Why do we need ADC and DAC? Draw the block diagram to interface 8085 microprocessor
with ADC and DAC. (N/D’11) (M/J 12)
13. Describe the comparison of I/O mapped and memory mapped I/O interfacing. (M/J 12)
14. Draw and explain the functional block diagram of 8259 PIC. (M/J 12)
15. Draw and explain the functional block diagram of 8237.
16. Draw and explain the functional block diagram of 8255 PPI with 8051
17. Draw and explain the functional block diagram of 8259 PIC with 8051
18. Draw and explain the functional block diagram of 8254 timer with 8051
19. Draw and explain the functional block diagram of 8279 with 8051
20. Draw and explain the functional block diagram of 8251 with 8051
21. Draw the block diagram to interface 8051 microprocessor with ADC and DAC
UNIT – V: MICRO CONTROLLER PROGRAMMING & APPLICATIONS
PART – A
1. List the different types of 8051 instructions. ( April/may -2010, Nov/Dec-2011)
The different types of 8051 instructions are:
a. Logical Instructions
b. Arithmetic Instructions
c. Data transfer Instructions
d. Branch Instructions
e. Jump & CALL Instruction
2. What are the various operations performed by Boolean variable instructions of 8051?(
April/may -2010, April/may -2011)
Boolean variable instructions perform the following operations
BOOLEAN OPERATOR MNEMONICS
AND(AND logical) ANL
OR(OR logical) ORL
NOT(COMPLEMENT) CPL
XOR(Exclusive OR logical) XRL
3. What is the operation of the given 8051 microcontroller instructions:
XRL A, direct? (April/may -2011)
XOR each bit of A with the same bit of the direct RAM address and the result is stored in A
(Acc).
4. Draw the flow chart for the programming of serial port of 8051 (May/June -2012)
5. What are the applications of 8051 microcontroller? (May/June -2012)
The applications of 8051 microcontroller are:
• Automobile
• Aeronautics
• Mobile communication
• Robotics
• Remote sensing etc.,
6. How is the pulse generated from microcontroller for stepper motor control (May/June -
2013)
To cause the stepper to rotate, we have to send a pulse to each coil in turn. The 8051 does not
have sufficient drive capability on its output to drive each coil, so there are a number of ways to
drive a stepper, Stepper motors are usually controlled by transistor or driver IC like ULN2003.
Driving current for each coil is then needed about 60mA at +5V supply.
7. State the functions performed by the instructions JBC and CJNE in 8051 microcontroller.
(May/June -2014)
•
to the status of carry flag or any bit addressable locations
•
8. Why do we need opto-isolator circuit between microcontroller and the stepper motor?
(Nov/Dec-2011)
Opto-isolator are widely used to isolate the stepper motor’s EMF voltage and keep it
form damaging the digital microcontroller system.
9. Why interfacing is needed for 1/0 devices? (Nov-2009])
Generally I/O devices are slow devices. Therefore the speed of I/O devices does not match with
the speed of microprocessor. And so an interface is provided between system bus and I/O
devices.
10. What is the operation carried out when 8051 executes the instruction MOVC A, @ A +
DPTR? (Nov-2007)
This instruction loads the accumulator from the contents of program memory whose address is
given by the sum of the contents of accumulator and contents of DPTR register (A) ‹— ((A) +
(DPTR))
11. Write program to load accumulator, DPH, &DPL using 8051? (Nov-2007)
MOV A,#30
MOV DPH, A
MOV DPL, A
12. Write a program to perform multiplication of 2 numbers using 8051? (NOV-2009)
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
13. Write a program to mask the 0th &7th bit using 8051? (APRIL-2009)
MOV A,#data
ANL A,#81
MOV DPTR,#4500
MOVX @DPTR,A
LOOP SJMP LOOP
14. 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
15. Explain PUSH and POP instructions in 8051.
PUSH-The stack pointer is incremented by one. The contents of the indicated variable is
then copied into the internal RAM location addressed by the stack pointer.
POP-Reverse of PUSH operation.
16. How many ports are bit addressable in an 8051 microcontroller?(N/D ‘12’)
In 8051 there are many bit-addressable registers such as A (ACC), B, SCON,
PCON, TCON, p0, p1, p2, p3.
17. Write a program to find the 2’s complement using 8051?( NOV-2008)
MOV A, R0
CPL A
INC A
18. Explain rotate instructions of 8051.
RL A,
RLC A,
RR A,
RRC A
19. Explain DAA instruction of 8051.
Decimal adjust accumulator for addition bytes
20. What does the mnemonics “LCALL” and “ACALL” stands for? (Nov/Dec-2012)
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.
21. What are the use of PWM in motor control using microcontroller?
The speed of the dc motor depends on the applied voltage. The average applied dc
voltage and power can be varied using a technique called pulse width modulation. In this
technique the dc power supply is not a voltage of fixed amplitude ie it is a pulsating DC
voltage. By changing the pulse width we can change the applied power.
22. Calculate the reload value of timer1 for achieving a baud rate of 4800in 8051 for a crystal
frequency of 11.0592MHz?
TH = 256 – k * Oscillatory frequency
-------------------------------
384 * Baud rate
= 256 – 1*11.0592*10E6 / 384*4800
= 250 = FAH
23. List the features of ADC0804?
i) 8-bit successive approximation ADC
ii) Access time is 135ns
iii) Conversion time is 100µs
iv) It has an on chip clock generator
v) It does not require any zero adjustment
vi) It operates on single 5V power supply.
24. What is the output of the program?
MOV R0, A
XRL A, # 3F H
XRL A, R0
The contents of A register will be 3F H and the contents of R0 will be the initial contents
of A
25. What are the different addressing modes of microcontroller 8051? ( A/ M -2008)
i) Register addressing
ii) Direct byte addressing
iii) Register indirect addressing
iv) Immediate addressing
v) Register specific
vi) Index
26. Give the PSW setting for making register bank 2 as default register bank in 8051
microcontroller ( M / J 2007)
MOV PSW, #10 ; SELECT BANK 2
MOV A, R0 ; (A) ‹— (R0) FROM BANK 2
MOV PSW, #00 ; SELECT BANK 0
CLR C ; CLEAR CARRY
SUBB A, R1 ; A ‹— A- (R1) FROM BANK 0
The above program is to subtract the contents of R1 of BANK0 from the contents of RO
of Bank 2.
PART - B
1. Draw the schematic for interfacing a stepper motor with 8051 microcontroller and write
8051 ALP for changing speed and direction of motor. (M/J 12)
2. Explain the data transfer instructions and program control instructions of 8051
microcontroller (A/M’11)
3. Write an assembly language program based on 8051 microcontroller instruction set to
perform four arithmetic operations on 2, 8 bit data. (A/M’11)
4. Explain the interfacing of Keyboard/Display with 8051 microcontroller. (A/M’11)
5. Explain the servomotor control using 8051 microcontroller. (A/M’11)
6. Explain with a program to rotate the stepper motor in both clockwise and anticlockwise
direction using 8051 microcontroller. (N/D’11)
7. How to interface a 7 segment display using 8051 microcontroller. (N/D’11)
8. How 8051 is used in washing machine control. (N/D’11) (M/J 12)
9. How do you interface a 4X4 matrix keyboard using 8051 microcontroller. (N/D’11)
10. Write short notes on LCD interface. [May-2009]
11. Explain the hardware and software program to interface 8051 with washing machine?
these 2 marks are really very useful. thankssssssssssssss.....................
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