Micro Processor And Micro controller

Prepared by: Mr.P.Raja Pirian Subject Code/Name: EC 8691 /MICROPROCESSORS & MICROCONTROLLERS
MP & MC 1. 8 KCE / ECE / QB / III Yr / MP & MC
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
UNIT I-THE 8086 MICROPROCESSOR
PART-A
1. What is the need for interrupts in microprocessor operation? (AU AM 2018)
 An interrupt is a condition that halts the microprocessor temporarily to work on a
different task and then return to its previous task.
 Interrupt is an event or signal that request to attention of CPU. This halt allows
peripheral devices to access the microprocessor.
 Whenever an interrupt occurs the processor completes the execution of the current
instruction and starts the execution of an Interrupt Service Routine (ISR) or
Interrupt Handler.
2. What are Byte and String Manipulation? (AU AM 2018)
 String is a series of data byte or word available in memory at consecutive locations.
 It is either referred as byte string or word string.
 Their memory is always allocated in a sequential order. Instructions used to
manipulate strings are called string manipulation instructions.
3. Define stack pointer. (AU AM 2018)
 A stack pointer is a specialized buffer which stores data from the top to down. As
new requests come in, they "push down" the older ones.
 The most recently entered request always resides at the top of the stack, and the
program always takes requests from the top.
4. List the various addressing modes of 8086. (AU ND 2017)
 Register Addressing mode :
 Immediate Addressing mode:
 Register Indirect Addressing mode:
 Direct Addressing mode:
 Indexed Addressing mode:
 Base Relative Addressing mode:
 Base Indexed addressing mode:
5. Define Macros. (AU ND 2017)
 Macros are small routines that are used to replace strings in the program. They can
have parameters passed to them, which enhances the functionality of the micro
itself.
 A Macro is a group of instructions with a name. When a macro is invoked, the
associated set of instructions is inserted in place in to the source, replacing the
macro name. Macros provide several powerful mechanisms useful for the
development of generic programs.
6. The offset address of a data is (341B)H and the data segment register value is
(123A)H. What is the physical address of the data? (AU AM 2017)
 Dada segment Address is (123A)H
 Base address of data segment is (123A0)H
 Physical address = Base address + Offset address
= (123A0) H+ (341B) H
= (157BB) H

7. List the flags of 8086 microprocessor. (AU ND 2016)
The flags are:
 Carry Flag, Parity Flag
 Auxiliary Flag, Zero Flag
 Sign Flag, Overflow
8. List the segment registers of 8086. (AU ND 2016)
The segment registers of 8086 are:
 Code Segment register
 Data Segment register
 Stack Segment register
 Extra Segment register
9. Write about the different types of interrupts supported in 8086? (AU AM 2015)
 The following are the different types of interrupts supported in 8086:
(i) Hardware Interrupt
 Maskable Interrupts
 Non-Maskable Interrupts
(ii) Software Interrupts
 256 Types of Software Interrupts
10.Identify the addressing modes in the following instruction. (AU AM 2014)
AND AL, BL - Register Addressing mode
SUB AL, 24H - Immediate Addressing mode
MOV AL, (BP) - Register Indirect Addressing mode
MOV CX, 1245H. - Direct Addressing mode
11.What is a tristate bus? (AU ND 2014 -2)
 A three-state bus is a computer bus connected to multiple tri-state output devices, only
one of which can be enabled at any point to avoid bus contention. This scheme allows
for the same bus to be shared among multiple devices.
 A three state (tri-state) device is a digital circuit that exhibits three states
They are :Logic 1 , Logic 0, High-impedance
12.What is an assembler? (AU ND 2014)
 An assembler is a program that takes basic computer instructions and converts them
into a pattern of bits that the computer's processor can use to perform its basic
operations.
 Assemblers need to:
(i) Translate assembly instructions and pseudo-instructions into machine instructions.
(ii) Convert decimal numbers, etc. specified by programmer into binary.
 Typically, assemblers make two passes over the assembly file:
(i) First pass: Reads each line and records labels in a symbol table.
(ii) Second pass: Use info in symbol table to produce actual machine code for each line.
13.Why is the 8086 memory divided into odd and even banks? (AU ND 2013)
 The address space is physically connected to a 16-bit data bus by dividing the address
space into two 8-bit banks of up to 512 k bytes each.
 One bank is connected to the lower half of the 16-bit data bus (D0 – D7) and contains
even address bytes, i.e., when A0 bit is low, the bank is selected.
 The other bank is connected to the upper half of the data bus (D8 - D15) and contains odd
address bytes, i.e., when A0 is high and BHE (Bus High Enable) is low, the odd bank is
selected. A specific byte within each bank is selected by address lines A1-A19.

14.What do you mean by segment override prefix? (AU ND 2013)
 A segment override prefix allows any segment register (DS, ES, SS, or CS) to be used as
the segment when evaluating addresses in an instruction.
 An override is made by adding the segment register plus a colon to the beginning of the
memory reference of the instruction as in the following examples:
MOV AX, [ES: 60126] ; Use ES as the segment
MOV AX, [CS: BX] ; Use CS as the segment
MOV AX, [SS: BP+SI+3] ; Use SS as the segment
15.What are the 8086 instructions used for BCD arithmetic? (AU AM 2013)
 DAA(DECIMAL ADJUST AFTER BCD ADDITION)-This instruction is used to make sure
the result of adding two packed BCD numbers is adjusted to a legal BCD number.
 DAS (DECIMAL ADJUST AFTER BCD SUBTRACTION)-This instruction is used after
subtracting one packed BCD number from another packed BCD number, to make sure
the result is correct packed BCD.
16.What are the 8086 instructions used for ASCII arithmetic? (AU ND 2013)
The 8086 instructions used for ASCII arithmetic are:
(i) AAA : ASCII adjust after addition
(ii) AAS : ASCII adjust after subtraction
(iii) AAM : ASCII adjust after multiplication
(iv) AAD : ASCII adjusts before division.
17.List the various string instructions available in 8086. (AU ND 2013)
The various string instructions of 8086 are:
(i) MOVS : Move byte or word string
(ii) MOVSB, MOVSW : Move byte, word string
(iii) CMPS : Compare byte or word string
(iv) SCAS : Scan byte or word string (comparing to A or AX)
(v) LODS, STOS : Load, store byte or word string to AL or AX
18.What are the contents of AL and CY after the execution of the
following segment? (AU AM 2013)
MOV BL, B5H
RCL BL, 3
MOV AL, BL
Output:
C=0 , BL=10110101
After 1strotation,C=1 ,BL=01101010
After 2ndrotation,C=0 ,BL=11010101
After 3rdrotation,C=1 ,BL=10101011
19.How clock signal is generated in 8086 microprocessor? (AU ND 2012)
 The clock signal of 8086 is generated using 8284 clock generator.
 The crystal is connected to the crystal oscillator input of 8284 to generate the clock
signal.
 The maximum internal frequency of 8086 is 5 MHz.
20.How will carry and zero flags reflect the result of the instruction
CMP BX, CX? (AU ND 2012)
 The carry and zero flags reflect the following result for CMP BX,CX instruction:
If BX>CX, carry flag=1
If BX=CX, zero flag=1
If BX<CX, carry flag=0

21.What is an assembler directive? Give two examples. (AU ND 2011)
 Assembler directives or pseudo instructions are to help the programmer to
communicate the program requirements to the assembler.
 Examples: ASSUME, DB, DD, DQ, DT, END, ENDS, ENDP, EQU etc.
22.What is a microprocessor? What is the difference between an MP and CPU?
(AU ND 2011)
 A microprocessor is a multipurpose programmable electronic device that reads binary
instruction from a memory, accepts binary data as input and processes the data
according to those instructions and provides result as output.
Microprocessor(MP) Central Processing Unit(CPU)
It is a packaged electronic
component.
It is the core of a computer or a
microprocessor.
It contains a CPU, I/O, and
memory access circuits.
It contains an "arithmetic/logical unit (ALU)"
that does the computational work, an
instruction fetcher, decoder and executer.
23.Why the program counter and stack pointer are registers of 16 bit?(AU ND 2011)
 In 8086 microprocessor these registers are used to access memory. Since maximum
capacity of 8085 is 64 k bytes program counter and stack counter are 16-bit(216=64 k)
 In 8086 microprocessor, program counter (IP) and stack pointer (SP) provide offset
for code segment and stack segment, respectively. The length of the offset for 8086
microprocessor is 16-bit, so program counter and stack pointer are 16- bit registers in
8086.
24.List any two external hardware synchronization instructions of 8086
microprocessor. (AU ND 2011)
The external hardware synchronization instructions of 8086 are,
(i) HLT-Halt (do nothing) until interrupt or reset.
(ii) WAIT -Wait(do nothing) until signal on the TEST pin is low.
(iii) ESC -Escape to external coprocessor such as 8087 or 8089
(iv) LOCK -An instruction prefix. Prevents another processor from taking the bus
25. What is the purpose of clock input? (AU ND 2010)
 The clock input provides the basic timing for processor operation and bus control
activity.
 It is an asymmetric square wave with 33% duty cycle.
 The range of frequency varies from 5MHz to 10MHz.
26.Write the advantages of memory segmentations.
 It allows the memory addressing capacity to be 1Mbyte even though the address
associated with individual instructions is only16 bit.
 It allows instruction code, data, stack, and portion of program to be more than 64KB
long by using more than one code, data , stack segment and extra segment.
 It facilitates use of separate memory areas for program, data and stack.
PART-B
1. For 8086 Microprocessor what are the instruction set and
assembler directives? (13)(AU ND 2018-3)
2. Explain the various addressing modes of 8086 microprocessor
with suitable examples. (13)(AU ND 2018)
3. Draw and explain the architecture of 8086 with neat diagram. (13)(AU AM 2018-3)
4. Describe the interrupts of 8086 and its types with service routine. (13)(AU AM 2018-3)

5. (i)Explain briefly about the internal hardware architecture of 8086
microprocessor with a neat diagram. (10)(AU ND 2016)
(ii)Write short note about assembler directives. (06)
6. Explain the various addressing modes of 8086 microprocessor
with suitable examples. ` (16)(AU ND 2016)
7. Define interrupts and their types. Write, in detail, about interrupt
service routine. (16)(AU AM 2014)
8. (i)Explain briefly about the internal hardware architecture of 8086
microprocessor with a neat diagram. (10)(AU AM 2014)
(ii)Write a 8086 ALP to convert BCD data to Binary data. (06)
9. (i)The data transfer rate of I/O Device ‘A’ is considerably less than that of the
microprocessor. Draw a flowchart of data transfer operation to be used.
(08)(AU AM 2014)
(ii)Describe the functions of execution unit and bus interface unit. (08)
10.(i) Develop a program to transfer 10 bytes of data from memory location starting from
2000H. (08)(AU AM 2014)
(ii)Describe program location control directives with suitable examples.
(08)
11.(i) Develop a program to multiply two 16 bit numbers stored in P1 and P2.
(08)(AU AM 2014)
(ii)Explain rotate and shift instructions with suitable examples. (08)
12.With neat diagrams explain the bus interfacing unit and
execution unit available in 8086 microprocessor. (16)(AU ND 2014)
13.Briefly explain the addressing modes in 8086 microprocessor
with example. (16)(AU ND 2014)
14.(i) Briefly explain the arithmetic group of instructions of 8086
processor. (08)(AU ND 2014)
(ii)Briefly explain the assembler directives available in 8086. (08)
15.(i) Explain the 8086 interrupt types in detail. (08)(AU AM 2013-4)
(ii)Describe how memory is accessed in 8086 with suitable diagram. (08)
16.(i)Explain the architecture of 8086 microprocessor. (08)(AU AM 2013-3)
17.(i)Describe the architecture of 8086 microprocessor with
neat diagram. (10)(AU ND 2013)
(ii)What are the differences between memory mapped I/O and
I/O mapped I/O. (06)
18.(i) What do you mean by assembler directives? Explain SEGEMENT,
TYPE, OFFSET with suitable examples. (08)(AU ND 2013)
(ii)Write an 8086 ALP to check whether the given string is
palindrome or not. (08)
19.(i)Discuss about the 8086 instruction used for transferring data
between registers, memory, stacks and I/O devices. (08)(AU ND 2012)
(ii)Write a program based on 8086 instruction set to multiply a
constant value to a sequence of data from 1 to n stored in memory.(08)
20.(i)Write a program based on 8086 instruction set to compute the average of ‘n’ number of
bytes stored in the memory. (08)(AU ND 2012-2)
(ii)Discuss about the various assembler directive in 8086
microprocessor programming. (08)

PART-C
1. (i) Discuss the data movement and program control instructions
of 8086. (10)(AU AM 2013)
(ii)Write an 8086 ALP to find the sum of numbers in the array of 10 elements. (05)
2. Write the 8086 assembly language program to arrange the set
of numbers in ascending order and explain. (15)(AU AM 2012)
3. (i) Explain the data transfer, arithmetic and branch instructions
with examples. (08)(AU AM 2014)
(ii) Write an 8086 ALP to find the sum of numbers in an array of 10 elements. (07)
4. (i)Write a program based on 8086 instruction set to compute the average of ‘n’ number of
bytes stored in the memory. (08) (AU ND 2012-2)
(ii)Discuss about the various assembler directive in 8086
microprocessor programming. (07)
5. (i)Write an 8086 ALP to separate odd and even numbers in a
given array. (07)(AU ND 2013)
(ii)Explain the data transfer group and logical group of 8086
instruction with necessary examples. (08)
UNIT II- 8086 SYSTEM BUS STRUCTURE
PART-A
1. Define System Bus. (AU ND 2018)
 Bus is a group of wires or lines that are used to transfer the addresses of Memory or I/O
devices. It us unidirectional.
 In Intel 8086 microprocessor, Address bus is of 16 bits. This means that Microprocessor
8086 can transfer maximum 16 bit address which means it can address 65,536 different
memory locations.
2. When is coprocessor used?
 A coprocessor is a computer processor used to supplement the functions of the primary
processor (the CPU).
 Operations performed by the coprocessor may be floating point arithmetic, graphics,
signal processing, string processing, cryptography or I/O interfacing with peripheral
devices.
3. List two differences between maximum mode and minimum mode configuration of
8086.
Sl.No Minimum mode Maximum mode
1. In minimum mode there can be
only one processor i.e. 8086.
In maximum mode there can be multiple
processors with 8086, like 8087 and 8089.
2. In minimum mode there can be
only one processor i.e. 8086.
In maximum mode there can be multiple
processors with 8086, like 8087 and 8089.
3. ALE for the latch is given by 8086
as it is the only processor in the
circuit.
ALE for the latch is given by 8288 bus
controller as there can be multiple
processors in the circuit.
4. What is meant by multiprogramming? (AU AM 2017)
 Multiprogramming is the technique of running several process at a time using
timesharing.
 It allows a computer to do several things at the same time.

5. What is the need of LOCK signal? (AU ND 2017)
 It is an active low pin.
 It indicates that other system bus masters have not been allowed to gain control of
the system bus while LOCK' is active low(0).
 The LOCK signal will be active until the completion of the next instruction.
6. Write some example for advanced processors. (AU ND 2017-2)
The examples for advanced processors are:
 80386, 80486
 Pentium-I, Pentium-II
 Pentium-III
7. Define machine cycle. (AU ND 2016)
 Machine cycle is defined as the time required to complete one operation. It includes 3 to
6 T-states.
 The machine cycle is a 4 process cycle that includes reading and interpreting the
machine language, executing the code and then storing that code.
8. Differentiate External verses Internal bus. (AU AM 2016)
 Internal Data Bus: The internal data bus only works inside a CPU that is internally. It is
able to communicate with the internal cache memories of the CPU. Since they are
internally placed they are relatively quick and are now affected by the rest of the
computer.
 External Data bus: This type of bus is used to connect and interface the computer to its
connected peripheral devices. Since they are external and do not lie within the circuitry
of the CPU they are relatively slower.
9. Compare closely coupled and loosely coupled configurations. (AU AM 2016-3)
Closely coupled configurations Loosely coupled configurations
A multiprocessor system with
common shared memory is known as
closely coupled System.
A multiprocessor system in which each
processor has its own private local memory
is known as loosely coupled system.
Here, the information can be shared
among the CPUs by placing it in the
common global memory.
Here, the information is transferred from
one processor to other by message-passing
system.
Parallelism can be implemented less
efficiently.
Parallelism can be implemented more
efficiently.
System structure is less flexible. System structure is more flexible.
10.Define bus. Why bus request and cycle stealing are required? (AU AM 2015)
 Bus is a group of wires to transfer data from source to destination.
 In the cycle stealing mode, the DMA controller obtains access to the system bus
using BR (Bus Request) and BG (Bus Grant) signals, which are the two signals
controlling the interface between the CPU and the DMA controller.
11.State the different data transfer schemes. (AU AM 2014)
There are two types of data transfer scheme:
 Synchronous
 It is the data method which is used when the IO and Microprocessor match in Speed.
To transfer a data to or from the device, the user program issues a suitable
instruction addressing the device. The data transfer is completed at the end of the
execution of the instruction.

 Asynchronous
 It is the data transfer method which is used when the speed of the IO device does not
match with the microprocessor. Asynchronous data transfer method is also known
as handshaking.
12.What are the advantages of memory mapped I/O over I/O-mapped I/O?
(AU AM 2014)
Sl.No. Memory mapped I/O I/O-mapped I/O
1 I/O is treated as memory. I/O is treated I/O.
2 16-bit addressing. 8- bit addressing.
3 More Decoder Hardware. Less Decoder Hardware.
4 Can address 216=64k locations. Can address 28=256 locations.
5 Less memory is available. Whole memory address space is available.
13.What is meant by loosely coupled configuration? (AU AM 2014)
 In Multiprocessor system, two 8086’s cannot be tied directly together.
 In a loosely coupled configuration a number of modules of 8086 can be through a
common system bus to work as a multiprocessor system.
14.When the 8086 processor is in ‘Max mode’ and ‘Min mode’? (AU AM 2013)
The 8086 provides MN/MX pin to select the mode of operation:
 MN/MX =1 for minimum mode and
 MN/MX =0 for maximum mode.
15.What is the function of LOCK and RQ/ GT signals? (AU AM 2013)
 LOCK signal indicates that other systems bus master will be prevented from gaining the
system bus, while LOCK signal is low. It is activated by the LOCK Prefix instruction and
remains active until the end of the next instruction.
 Request / Grant Signals:
 In a maximum mode configuration, the minimum mode HOLD, HLDA interface is also
changed. These two are replaced by request/grant lines RQ/ GT0 and RQ/ GT1,
respectively.
 It is used for bus requests and bus grants.
16.State the functions of queue status lines QS0 and QS1 in 8086. (AU ND 2012)
1QS and 0QS - Queue status: The queue status bits shows the status of the internal
instruction Queue. QS1 and QS0 reflect the status of the instruction queue. This status
indicates the activity in the queue during the previous clock cycle.
The encoding of these signals is as follows:
QS0 QS1 Function
0 0 No operation, queue is idle
0 1 First byte of opcode
1 0 Queue is empty
1 1 Subsequent byte of opcode
17.In what ways are the microprocessor and co-processor differ? (AU ND 2012-2)
 A microprocessor is a multipurpose, programmable logic device that reads binary
instructions from a storage device called memory, accepts binary data as input and
processes data according to those instructions and provides result as output.
 The Coprocessor is a processor which is specially designed processor to work under the
control of the microprocessor and to support special processing capabilities.

18.List any four 8087 data formats. (AU AM 2012)
The following are the few data formats of 8087:
 Word integer
 Short integer
 Short real
 Long real
19.What are the features of closely coupled multiprocessor systems? (AU ND 2011)
The features of closely coupled multiprocessor systems are:
 A multiprocessor system with common shared memory.
 Parallelism can be implemented less efficiently.
 System structure is less flexible.
20.Write the advantages of loosely coupled system over tightly coupled systems?
The following are the advantages of loosely coupled system over tightly coupled systems:
 High system throughput can be achieved by having more than CPU.
 The system can be expanded in a modular form. Each bus master module is an
independent unit and normally resides on a separate PC board.
 A failure in one module normally does not cause a breakdown of the entire system and
the faulty module can be easily detected and replaced.
 Each bus master may have a local bus to access dedicated memory or IO devices so that
a greater degree of parallel processing can be achieved.
21.What is the use of MN/MX signals in 8086?
 It is used to operate the microprocessor in two operating modes i.e. maximum and
minimum mode.
 The minimum mode is used for small systems with a single processor.
 The maximum mode is used for systems with a Multiple processor.
22.What is the difference between uni-programming and Multiprogramming?
The differences between uni-programming and multiprogramming are:
Uni-programming Multiprogramming
Programming unit which performs
an independent task
The code for two or more processes
is in a memory at the same time
Processes are executed in a serial
fashion
Processes are executed in a
multiplexed fashion.
23.What is the use of instruction queue in 8086 microprocessor?
 The queue operates on the principle of first in first out (FIFO). So that the execution unit
gets the instruction for execution in the order they fetched.
 Feature of fetching the next instruction while the current instruction is executing is
called pipelining which will reduce the execution time.
24.Explain the BHE and LOCK signals of 8086.
BHE (Bus High Enable): Low on this pin during first part of the machine cycle indicates
that at least one byte of the current transfer is to be made on higher byte AD15-AD8.
LOCK: This signal indicates that an instruction with a LOCK prefix is being executed and the
bus is not to be used by the other processor.
25.What are the signals used in 8086 maximum mode operation?
The Signals used in 8086 Maximum Mode of Operation are:
 QS1 , QS0
 S2, S1 ,S2
 LOCK,
 RQ/GT1, RQ/GT0

26.Give the register classification of 8086.
The 8086 contains:
 General purpose registers: They are used for holding data, variables and intermediate
 results temporarily.
 Special purpose registers: They are used as segment registers, pointers, index register
or as offset storage registers for particular addressing modes.
27.What are pointers and index registers?
 IP, BP and SP are the pointers and contain offsets within the code, data and stack
segments respectively.
 SI and DI are the index registers, which are used as general purpose registers and also
for offset storage in case of indexed, based indexed and relative based indexed
addressing modes.
PART-B
1. Distinguish between closely coupled and loosely coupled
multiprocessor configurations. (13)(AU ND 2018)
2. What do you understand from system bus structure? Explain. (13)(AU ND 2018)
3. Explain the closely looped configuration with neat diagram. (13)(AU ND 2017-2)
4. Explain the following: (AU AM 2016)
(i)Multiprocessor system. (04)
(ii) Coprocessor (04)
(iii) Multiprogramming (04)
(iv) Semaphore (04)
5. Write an ALP to check whether the given string is palindrome or not. (08)(AU AM 2015)
6. (i)Draw and explain the minimum mode configuration of 8086
microprocessor. (08)(AU ND 2014)
(ii)Briefly explain the architectural advancements of microprocessor.(08)
7. Write notes on
(i) Maximum mode in 8086 (08)
(ii) Interrupt processing (08) (AU AM 2014)
8. (i) How the interrupt vector is handled in 8086? (08) (AU ND 2013)
(ii) Explain the timing diagram of write cycle in 8086 in minimum mode. (08)
9. Describe the maximum mode signals, bus cycles, and maximum mode system configuration
of 8086 Microprocessor in detail. (16)(AU ND 2012)
10.(i) Draw the pin diagram of 8086 microprocessor and list the pin details.
(08)(AU ND 2011)
(ii)Explain the bus structure of 8086 microprocessor (08)
11.Explain Min/Max mode of 8086 microprocessor. (16)(AU AM 2011-2)
12.Explain in detail about closely coupled configuration of multiprocessor configuration with
suitable diagram. (16) (AU AM 2010-3)
13.Explain in detail about Loosely Coupled Multiprocessor configuration.
(16) (AU AM 2010-3)
(i) Explain in detail about the system bus timing of 8086/8088. (16)
14.Write notes on the following (16)
(i) Programmed I/O
(ii) Interrupt I/O
PART-C
1. Discuss the maximum mode configuration of 8086 with a neat diagram.
Mention the functions of various signals. (15)(AU ND 2018-2)

2. Discuss about the multiprocessor configurations of 8086. (13)(AU AM 2018-2)
3. Explain the system bus structure of 8086. Draw the timing
diagram for interrupt acknowledgement cycle. (13)(AU ND 2017-2)
4. Explain in detail about the system bus timing of 8086. (16)(AU ND 2016-2)
5. Describe the minimum mode 8086 system and its timing diagram. (15)(AU AM 2013)
UNIT-III – I/O INTERFACING
Part – A
1. Why is memory interfacing required? (AU ND 2018)
 While executing an instruction, there is a necessity for the microprocessor to access
memory frequently for reading various instruction codes and data stored in the
memory.
 The interfacing circuit aids in accessing the memory. Memory requires some signals
to read from and write to registers.
2. What are the differences between LED display and LCD display? (AU ND 2018)
LED LCD
Definition
PN-Junction device which
discharge visible lights when
an electrical charge passes
through it.
It is an optical device used for displaying
the information in the form of text and
images.
Stand For Light Emitting Diode Liquid Crystal Display
Backlight No backlight
Cold cathode fluorescent lamp provides
backlight.
Resolution High Low
3. Give the various modes and applications of 8254 timer? (AU AM 2018)
The various modes and applications of 8254 timer are,
Mode 0: Interrupt On Terminal Count
Mode 1: Hardware Retriggerable one shot
Mode 2: Rate Generator
Mode 3: Square Wave Generator
Mode 4: Software Triggered Strobe
Mode 5: Hardware Triggered Strobe
4. What is the handshake signals used in Mode-2 configuration of 8255?
(AU ND 2017)
 In mode2 only port A can be used as a bidirectional port.
 The handshaking signals are provided on five lines of port C (PC3-PC7). Port B can be
used in mode0 or in mode1.
5. How the DMA operation performed with 8086? (AU ND 2017)
 The direct memory access DMA interface of the 8086 minimum mode consist of the
HOLD and HLDA signals.
 When an external device wants to take control of the system bus, it signals to the 8086
by switching HOLD to the logic 1 level.
6. Draw the format of read back command register of 8254. (AU AM 2017)
D7 D6 D5 D4 D3 D2 D1 D0
1 1 COUNT STATUS CNT2 CNT1 CNT0 0
 D7-D6 = 1 for read back command register

 D5 Latch count
 D4 Latch status
 D3 select counter 2
7. What is the drawback of memory mapped I/O? (AU ND 2016)
Drawbacks of memory mapped I/O are:
 Memory mapped I/O scheme utilizes memory reference instructions, which are three
byte instructions.
 Due to wider port address, the interface of hardware is also complicated.
 The complexity of the program is large.
8. How DMA is initiated? (AU ND 2016)
 The device requests the CPU through a DMA controller to hold its data, address and
control bus, so that the device may transfer data directly to/from memory.
 The DMA data transfer is initiated only after receiving HLDA signal form the CPU.
9. List the advantages and disadvantages of parallel communication over serial
communication. (AU AM 2016)
Basis For Comparison Serial Transmission Parallel Transmission
Meaning
Data flows in bi-direction,
bit by bit.
Multiple lines are used to
send data i.e. 8 bits or 1 byte
at a time.
Cost Economical Expensive
Bits transferred at 1
clock pulse
1 bit 8 bits or 1 byte
Speed Slow Fast
Applications
Used for long distance
communication. Ex.PC to PC.
Short distance. Ex. Computer
to printer.
10.What is key bouncing? (AU AM 2016)
 Bouncing is the tendency of any two metal contacts in an electronic device to
generate multiple signals as the contacts close or open.
 Mechanical switches are used as keys in most of the keyboards.
 When a key is pressed the contact bounce back and forth and settle down only after
a small time delay (about 20ms).
 Even though a key is actuated once, it will appear to have been actuated several
times. This problem is called Key Bouncing.
11.What is key debouncing? (AU AM 2014 -3)
 The push button keys when pressed, bounces a few times, closing and opening the
contacts
 before providing a steady reading.
 So reading taken during bouncing may be faulty.
 Therefore the microprocessor must wait until the key reach to steady state. This is
known as key debounce.
12.What is direct memory access? (AU ND 2014 -3)
 Direct memory access (DMA) is a method that allows an input/output (I/O) device
to send or receive data directly to or from the main memory, bypassing the CPU to
speed up memory operations.
 The process is managed by a chip known as a DMA controller (DMAC)

13.What is a sample and hold circuit? (AU ND 2014 -3)
 The sample and Hold circuit is used to convert the analog signal into digital signal by
using the RC circuit.
 The capacitor holds the value of the signal for a particular time interval.
 The analog signal is sampled once for the RC time constant value.
14.What are the advantages of Programmable Interval Timer / Counter IC?
(AU AM 2014)
The 8253 is a programmable counter/timer chip designed for use as an Intel
Microcontroller peripheral. The main uses of 8253 are as follows:
 Interrupt a time sharing operating system at evenly spaced intervals so that it can
switch a program.
 Programmable on shot generator
 Serves as a programmable baud rate generator.
 Measure time delays between external events
 Count the number of times an event occurs.
 Causes the processer to be interrupted after a programmed number of external
events have occurred.
 Act as a Real time clock.
15.State the applications of Programmable Interval Timer. (AU AM 2013-3)
Applications of PIT 8254 are:
 Real time clock Event-counter
 Digital one-shot Programmable rate generator
 Square wave generator Binary rate multiplier
 Complex waveform generator Complex motor controller
16.What are the basic modes of operation of 8255? (AU ND 2013)
There are two basic modes of operation of 8255. They are:
 I/O mode, There are three modes.
 Mode 0 - Simple input/output
- Outputs are latched. Inputs are buffered. Do not have handshake.
 Mode 1 - Input/output with handshake
- Input or output data transfer is controlled by handshake signals.
 Mode 2 - Bidirectional I/O data transfer
- Bidirectional. Both inputs and outputs are latched.
 BSR mode
 The individual bits of Port C can be set or reset by sending out a single OUT
instruction to the control register.
 When Port C is used for control/status operation, this feature can be used to set or
reset individual bits.
17. List the display modes of 8279 keyboard/display controller. (AU ND 2012)
The display modes of 8279 are:
 Scanned keyboard mode
 Scanned sensor matrix
 Strobed input.
18.Define resolution of A/D converter. (AU AM 2012)
Resolution of A/D converter is defined as a ratio of change in value of input voltage Vi,
needed to change the digital output by 1 LSB. If the full scale input voltage required to cause
a digital output of all 1’s is ViFS, then the resolution can be given as,
Resolution =ViFS / (2n-1).

19.Draw the sample and hold circuit. (AU ND 2012)
Fig : Sample and Hold Circuit
20.State the advantages of DMA. (AU ND 2011- 2)
The advantages of DMA are:
 It allows the transfer between I/O and memory without CPU intervention.
 It is a hardware control transfer and hence it is very fast.
 Increased throughput
 Reduced power requirements
21.What are the modes used in keyboard mode? (AU ND 2010)
The modes used in keyboard mode are:
 Scanned keyboard mode with 2 key lockout
 Scanned keyboard with N – key rollover
 Scanned key board with special error mode
 Sensor matrix mode
 2-key lock out: Simultaneous key depression is not allowed.
 N-key rollover: Each key depression is treated independently from all others
22.Name the peripheral ICs used for parallel and serial data transfer. (AU AM 2010)
The following are the peripheral ICs used for parallel and serial data transfer,
 For Parallel communication : 8255 – Programmable Peripheral Interface
 For Serial Communication : 8251 – Serial Communication Interface.
23.Give the salient features of Programmable Interval Timer. (AU-ND 2010)
The Programmable Interval Timer is used as:
 Programmable rate generator
 Real time clock
 Digital one shot
 Complex motor controller
24.What is the use of stepper motor?
 Stepper motors are widely used in industrial, medical, consumer electronics application.
 In simple words, anywhere precision rotation or positioning of an object is needed.
25.Draw the FIFO Status register format
The FIFO status register format is given below,
D S/E O U F N N N
D - Display unavail.
S/E - Multiple keys pressed
O - Full and overrun
U - Read when Empty
F - FIFO full
N - Characters is FIFO

26.What is I/O mapped I/O?
 This is one of the techniques for interfacing I/O devices with μp.
 In I/O mapped I/O, the I/O devices assigned and identified by 8-bit addresses.
 To transfer the data between MPU and I/O devices I/O related instructions (IN and
OUT) and I/O control signals (IOR, IOW) are used.
PART-B
1. How are D/A and A/D interfaces used? Explain. (13) (AU ND 2018)-2)
2. What are interrupt controller and DMA controller? Explain. (13) (AU ND 2018)-2)
3. Draw the block diagram and explain the operations of USART. (13)(AU AM 2018)
4. Explain in detail about DMA controller with its diagram. (13)(AUAMD 2018-2)
5. Draw and explain the functional diagram of keyboard and display controller.
(13) (AU ND 2017)
6. Draw and explain the functional diagram of parallel communication interfacing chip.
(13)(AU AM 2017)
7. Explain the need of DMA controller with its functional diagram. (13)(AU AM 2017-3)
8. (i) Explain the function of programmable peripheral interface – Intel 8255.
(08) (AU AM 2014 -4)
(ii)Draw the block diagram to interface a analog to digital converter with a microprocessor
and explain its working. (08) (AU AM 2014-3)
9. (i) Draw a schematic to interface keyboard and display with 8086 using 8255 and explain.
(08) (AU AM 2014)
(ii) Write notes on Programmable Interval Timers (PIT) 8253 and 8254.
(08) (AU AM 2014 -2)
10.With a neat block diagram explain the key board and display controller IC 8279.
(16) (AU ND 2014 -2)
11. (i) With neat block diagram explain the 8251 and its operating modes. (08)
(ii)Draw the block diagram of I/O interface & explain in detail. (08)
12.Explain in detail about DMA controller. (16)
13.Write short notes on
(i)LED display (08)
14.LCD display (08)
15.Explain in detail about the asynchronous communication. (16)
16.Explain in detail about the synchronous communication. (16)
17.Explain in detail about interrupt controller. (16)
18.Discuss in detail about memory mapped I/O and I/O mapped I/O
with necessary diagram. (16)
PART-C
1. Draw and explain the block diagram of alarm controller. (15) (AU AM 2016)
2. Draw the block diagram of traffic light control system using 8086. Write the algorithm an
ALP for traffic light control system. (15)(AU AM 2018)
3. Draw the diagram to interface a stepper motor with 8051 microcontroller and write ALP to
run a stepper motor in both forward and reverse direction with delay.
(15)(AU AM 2018)
4. Describe the different modes of operation of timers/counters in 8051 with its associated
registers. (15)(AU AM 2018)
5. Draw and explain the functional diagram of 8251. (15)(AU ND 2017)

UNIT IV- MICROCONTROLLER
PART A
1. How microcontroller is different from microprocessor? (AU ND 2018)
The difference between microprocessor and microcontroller are given below,
Microprocessors Microcontrollers
A microprocessor is a single
chip CPU
Microcontroller is a single IC, contains a CPU and
much of remaining circuitry of a complete
computer (e.g., RAM, ROM, serial interface, parallel
interface, timer, interrupt handling circuit)
Microprocessors are commonly
used as a CPU in computers
Microcontrollers are found in small, minimum
component designs performing control oriented
activities
2. How to set 8051 in idle mode? (AU ND 2017)
PCON Register: Power control register
PCON (Power control) register is used to force the 8051 microcontroller into power saving
mode. Power control register of 8051 contains two power saving mode bits
 Bit 1 – PD: Power Down
1 = Enable Power Down mode. In this mode, Oscillator clock turned OFF and both CPU
and peripherals clock stopped. Hardware reset can cancel this mode. 0 = Disable Power
down mode.
 Bit 0 – IDL: Idle
1 = Enable Idle mode. CPU clock turned off whereas internal peripheral module such as
timer, serial port, interrupts works normally. Interrupt and H/W reset can cancel this
mode. 0 = Disable Idle mode.
3. Illustrate the DJNZ instruction. (AU ND 2017)
DJNZ <dest-byte>,<scr-byte>,rel
The DJNZ instruction decrements the byte indicated by the first operand and if the resulting
value is not zero, branches to the address specified in the second operand.
4. Which port used as multifunction port? List the signals. (AU AM 2017)
 All port pins of port 3 are multifunctional.
 Each pin of port 3 can be programmed to use as I/O or as one of the alternate
function.
 The signals are RD,WR,T1,T0,INT1, INT0,TXD and RXD.
5. Illustrate the CJNE instruction. (AU AM 2017)
CJNE <dest-byte>,<scr-byte>,rel
The CJNE instruction compares the first two operands and braches to the specified
destination if their values are not equal. If the values are the same, execution continues
with the next instruction.
6. What are the different ways of operand addressing in 8051? (AU ND 2016)
MOV A,#6AH
Here the data 6A is the operand, often known as source data. When this instruction is
executed, the data 6AH is moved to accumulator A. There are 5 different ways to execute
this instruction by using 5 addressing modes for 8051. They are (i) Immediate addressing
mode (ii)Direct addressing mode (iii) Register direct addressing mode (iv) Register indirect
addressing mode (v) Indexed addressing mode.

7. Write an 8051 ALP to toggle P1 a total of 200 times. Use RAM location 32H to hold
your counter value instead of registers R0-R7. (AU ND 2016-2)
MOV P1, #55H ; P1=55H
MOV 32H, #200 ; load counter value into RAM loc 32H toggle P1
LOOP: CPL P1
ACALL DELAY
DJNZ 32H, LOOP ; repeat 200 times
8. Draw the pin diagram of 8051. (AU ND 2016)
The pin diagram for 8051 is:
9. How do you select the register bank in 8051 microcontroller? (AU AM 2015)
 By default, the 8051 microcontroller is powered up with register bank 0; and, by using
the Program Status Word (PSW), we can switch to other banks. The two bits of PSW are
used for switching between the register banks. These two bits are accessed by the bit-
addressable instructions SETB and CLR.
 Based on the possible combinations of RS1 and RS0 of PSW, the register bank is changed
accordingly, i.e., if RS1 and RS0 are 0, then the Bank 0 is selected. Similarly, Bank1, 2&3
are selected as per the values of RS1 and RS0.
10.Draw the diagram for Processor Status Word in 8051. (AU AM 2015)
The diagram for PSW is given by,
C AC F0 RS1 RS0 OV F1 P
C - Carry
AC - Auxiliary Carry
F0 - User flag 0
RS1,RS0 - Register Bank Select
OV - Overflow
F1 - User flag 1
P - Parity

11.How the processor 8051 knows whether on chip ROM or External program memory
is used? (AU AM 2014-2)
Internal ROM
The 8051 has 4k (4096 locations) of on-chip ROM. This is used for storing the system
program. 212 = 4096, therefore the internal ROM address bus is 12 bits wide and internal
ROM locations go from 000H to FFFH.
Internal RAM
There are 256 bytes of internal RAM on the 8051. 28 = 256, therefore the internal RAM
address bus is 8 bits wide and internal RAM locations go from 00H to FFH. The first 128
locations (00H to 7FH) of internal RAM are used by the programmer for storing data while
the second 128 locations (80H to FFH) are the Special Function Registers (SFRs). EA-bar -
the external access, on pin 31, is used for enabling or disabling the on-chip ROM.
 When tied high (5V), the 8051 executes instructions in internal ROM when executing in
the lower 4k (8k for the 8052) of memory.
 If tied low the 8051 will always execute instructions in external memory.
12.Why it is necessary to have external pull-up for port 0 in 8051. (AU ND 2014)
Port 0 needs pull-up resistors to be connected externally if it is to be used as output port,
because it has no in built pull up circuit so it can't give +5v as output.
13.List the SFRs involved in interrupt programming of 8051. (AU ND 2014)
The SFRs involved in interrupt programming of 8051:
(i) SFR/ IE - Interrupts Enable Control
(ii) SFR/ IP - Interrupt Priority control
14.How the selection of particular register bank is done in 8051? (AU AM 2013)
The selection is done using the SFR, Program Status Word (PSW) Register.
C AC F0 RS1 RS0 OV F1 P
 RS means Register bank Select bits. RS0 and RS1 are used to select the register banks.
 00 - Register bank 0
15.What is difference between AJMP and LJMP instruction? (AU AM 2014)
The difference between the AJMP and LJMP instructions are given below,
AJMP LJMP
Description: Absolute Jump Description: Long jump
Jumps unconditionally to the
indicated code address within 2k
Block.
Jumps unconditionally to the
specified code address
16.How do you place a specific value in DPTR register? (AU ND 2013)
 DPTR consists of two separate registers: DPH (Data Pointer High) and (Data Pointer
Low).
 The Data Pointer (DPTR) is the 8051s only user-accessible 16-bit (2-byte) register. The
Accumulator, "R" registers, and "B" register are all 1-byte values.
 DPTR, as the name suggests, is used to point to data. It is used by a number of
commands which allow the 8051 to access external memory. When the 8051 accesses
external memory it will access external memory at the address indicated by DPTR.

17.Which of the 8051 ports need pull-up resisters to function as an I/O port?
(AU ND 2013)
Port 0 needs the pull-up resistor to function as an I/O port:
 It can be used for input or output.
 To use the pins of port 0 as both input and output each pin must be connected
externally to a 10 k pull-up resistor.
 This is due to the fact that P0 is an open drain, unlike P1, P2, and P3
 With resistors connected to port 0, in order to make it an input, the port must be
programmed by writing 1 to all the bits.
Dual role of port 0:
 Port 0 is also designated as AD0 - AD7, allowing it to be used for both address and data.
 When connecting an 8051/31 to an external memory, port 0 provides both address and
data.
 The 8051 multiplexes address and data through port 0 to save pins.
18.What is the difference between MOVX and MOV? (AU ND 2013)
MOV: Move Memory
Description: MOV- copies the value of operand2 into operand1. The value of operand2 is
not affected. Both operand1 and operand2 must be in Internal RAM. No flags are affected
unless the instruction is moving the value of a bit into the carry bit in which case the carry
bit is affected or unless the instruction is moving a value into the PSW register.
MOVX: Move Data To/From External Memory (XRAM)
Description: MOVX moves a byte to or from External Memory into or from the
Accumulator.
19.What is the special function registers used for port operation in 8051?
(AU AM 2012)
The following ports have been used as Bit addressable ports in 8051:
 PORT P0: When there is no external memory present, this port acts as a general
purpose input/output port. In the presence of external memory, it functions as a
multiplexed address and data bus. It performs a dual role.
 PORT P1: This port is used for various interfacing activities. This 8-bit port is a normal
I/O port i.e. it does not perform dual functions.
 PORT P2: Similar to PORT P0, this port can be used as a general purpose port when
there is no external memory but when external memory is present it works in
conjunction with PORT PO as an address bus. This is an 8-bit port and performs dual
functions.
 PORT P3: PORT P3 behaves as a dedicated I/O port
20.What are the different ways of operand addressing in 8051? (AU AM 2011 -2)
The addressing modes in 8051 are:
 Immediate Addressing mode.
 Register Addressing mode.
 Direct Addressing mode.
 Indirect Addressing mode.
 Relative Addressing mode.
 Absolute Addressing mode.
 Indexed Addressing mode.

21.What is need for bitwise instructions in microcontroller? (AU AM 2012)
 Bitwise instructions in microcontroller intended for bitwise operations to make control
programs more compact.
 Similar to logic instructions, bit-oriented instructions perform logic operations. The
difference is that these are performed upon single bits.
Bit-oriented Instructions
Mnemonic Description Byte Cycle
CLR C Clears the carry flag 1 1
CLR bit Clears the direct bit 2 3
SETB C Sets the carry flag 1 1
SETB bit Sets the direct bit 2 3
CPL C Complements the carry flag 1 1
CPL bit Complements the direct bit 2 3
ANL C,bit AND direct bit to the carry flag 2 2
ANL C,/bit AND complements of direct bit to the carry flag 2 2
ORL C,bit OR direct bit to the carry flag 2 2
ORL C,/bit OR complements of direct bit to the carry flag 2 2
MOV C,bit Moves the direct bit to the carry flag 2 2
MOV bit,C Moves the carry flag to the direct bit 2 3
22.How many ports are bit addressable in 8051? (AU ND 2011)
 Input/output ports named P0, P1, P2 and P3 has got four corresponding port registers
with same name P0, P1, P2 and P3.
 Data must be written into port registers first to send it out to any other external device
through ports.
 Similarly any data received through ports must be read from port registers for
performing any operation. All 4 port registers are bit as well as byte addressable. The
physical address of
 Port 0 is 80
 Port 1 is 90
 Port 2 is A0
 Port 3 is B0
23.What is the hardware and software interrupts of 8051µc? Mention its vector
addresses? (AU ND 2011)
The hardware and software interrupts of 8051 and their vector addresses are given below:
Interrupts Vector address
 INT0-External hardware interrupt0 - 0003H
 T0-Timer 0 interrupt - 000BH
 INT1-External hardware interrupt 1 - 001BH
 T1-Timer 1 interrupt - 001BH
24.What are the advantages of using a microcontroller in place of a microprocessor?
(AU AM 2011)
The advantages of using a microcontroller in place of a microprocessor are:
 Flexibility, Faster speed of execution
 Inexpensive, Rigid

25.List the different types of 8051 instructions. (AU AM 2010)
The types of 8051 instructions are:
 Arithmetic Instructions
 Branch Instructions
 Data Transfer Instructions
 Logic Instructions
 Bit-oriented Instructions
26.What is the function of RET instruction in 8051? (AU ND 2010)
RET: Return from Subroutine
Description: RET is used to return from a subroutine previously called by LCALL or ACALL.
Program execution continues at the address that is calculated by popping the topmost 2
bytes off the stack. The most-significant-byte is popped off the stack first, followed by the
least-significant-byte.
PART B
1. What are special function registers? Explain. (13) (AU ND 2018)
2. Discuss on the different addressing modes of 8051 with suitable examples.
(13) (AU AM 2018)
3. Write the available special function registers in 8051. Explain each register with its format
and functions. (13) (AU ND 2017)
4. Discuss the ports and its circuits of 8051. (13) (AU AM 2017)
5. Write an ALP using 8051 instructions to receive byte of data serially and put them in P1. Set
the baud rate at 4800, 8-bit data, and 1 stop bit. (16) (AU ND 2016)
6. Explain the architecture of 8051 with its diagram. (16) (AU AM 2016-2)
7. Write an 8051 ALP to create a square wave of 66 % duty cycle on bit 3 of port 1.
(16) (AU ND 2015)
8. (i) Explain the architecture of 8051 microcontroller with neat diagram.
(10) (AU AM 2015)
(ii)Explain the TMOD function register and its timer modes of operations.
(06)
9. (i) Enumerate about the ports available in 8051 microcontroller. (08) (AU AM 2014)
(ii)Write an assembly language program for 8051 to find the largest of three numbers.
(08)
10. (i) Describe the serial interface with 8051 microcontroller. (08) (AU AM 2014)
(ii)Write an assembly language program for 8051, to send 20 output lines at P2.0 vary the
duration of pulse using NOP. (08)
11. (i) Explain in detail the memory organization of 8051 microcontroller.
(16) (AU ND 2014)
12. (i) Draw the pin diagram of 8051 microcontroller and explain the function of each pin.
(10) (AU AM 2013)
(ii) Discuss briefly the various registers in 8051 microcontroller. (06)
13. (i)Explain the working of program control transfer instructions of 8051 microcontroller.
(08)(AU AM 2012)
(ii) Write an assembly language program to generate square wave form using on-chip
timer. (08)
14. List the features of 8051 microcontroller. (16) (AU AM 2012)
15. Explain the architecture of 8051 microcontroller with a neat diagram.
(16) (AU AM 2011)

16. Describe the different mode of operation of timers/counters in 8051 with its associated
register. (16)(AU AM 2011)
17. (i) Explain the different types of addressing modes in 8051. (08) (AU AM 2011)
(ii) Explain the arithmetic instructions of 8051. (08)
18. (i) Explain the memory organization of 8051 microcontroller. (08) (AU AM 2010)
(ii) Explain the parallel I/O and serial I/O of 8051. (08)
19. Draw the functional block diagram of 8051 and explain. (16) (AU AM 2010)
20. Explain the working of the 8051 microcontroller .Give a neat sketch.
(16) (AU ND 2010)
21. . Write an 8051 assembly language program to multiply the given number 48H and 30H.
PART C
1. Describe the architecture of 8051 with neat diagram. (15) (AU AM 2018)
2. (i) Write a brief notes on external data move operations in 8051. (05) (AU ND 2013)
(ii)Write an 8051 assembly language program to add three BCD numbers stored in internal
RAM locations 25H, 26H, and 27H and put the result in RAM locations 31H (MSB) and
30 H (LSB). Use register R0 to store the intermediate result. (10)
3. Write an assembly language program using 8051 instructions to arrange an array of
numbers in ascending order. (15) (AU AM 2010)
4. (i) Briefly explain the data transfer instructions available in 8051 Microcontroller
(08) (AU ND 2014)
(ii) Using timers in 8051, write a program to generate square wave for 100ms with 50%
duty cycle. (07)
5. (i) How are the timers of 8051 used to produce time delay in timer mode?
(08) (AU ND 2011)
(ii) Explain the interrupt structure of 8051 microcontroller. (07)
UNIT V- INTERFACING MICROCONTROLLER
PART –A
 How to program 8051 Timers? (AU ND 2018)
 The timers in the 8051 have both start and stop signal..
 The start and stop of the timer are controlled by way of software by the TR
(timer start) bits TRO and TR1.
 And it is achieved by the instructions “SETB TR1″ and “CLR TR1″ for Timer 1, and
“SETB TRO” and “CLR TRO” for Timer 0.
 What are the types of ADC? (AU ND 2018)
The following are the various ADC used with microprocessor
 Flash ADC
 Sigma-delta ADC
 Dual slope converter
 Successive approximation converter
 What are the types of sensor used for interfacing? (AU AM 2018)-2
The types of sensor used for interfacing are
 Temperature Sensor
 IR Sensor
 Ultrasonic Sensor
 Touch Sensor, Proximity Sensors
 Pressure Sensor, Level Sensors
 Smoke and Gas Sensors

 List the 8051 interrupts with its priority. (AU ND 2018-3)
The 8051 interrupts with its high to low priority are,
 External Interrupt 0 (INT0)
 Timer Interrupt 0 (TFO)
 External Interrupt1 (INT1)
 Timer Interrupt1 (TF1)
 Serial communication (RI+TI)
 Give two examples of sensors and state its uses. (AU ND 2017)
The examples of sensors are:
 Thermocouples have the widest temperature range of all the temperature sensors
from below -200oC to well over 2000oC.
 LM35 Temperature sensors are used in measuring temperature of a particular
environment and HVAC applications, providing thermal shutdown for a component/
circuit and checking battery temperature.
 List the modes of timer in 8051. (AU ND 2016)
Four timer modes are available in 8051:
M1 M2 Mode Description
0 0 Mode 0 13-bit Timer
0 1 Mode 1 16-bit Timer
1 0 Mode 2 8-bit auto reload
1 1 Mode 3 Split Timer mode
 State how baud rate is calculated for serial data transfer in mode 1. (AU ND 2016)
 Using Timer/Counter 1 to generate Baud rates,
Baud rate = K x Oscillator frequency/ 32 x 12 x [(256-TH1]
If SMOD=0 then K=1
If SMOD=1 then K=2 (SMOD is the PCON register)
 Using Timer/Counter 1 to generate Baud rates,
Baud rate = Timer 2 overflow rate/16
 Compare polling and interrupt. (AU AM 2016)
The 8051 microcontroller can do only one task at a time.
 In polling, the microcontroller continuously checks each port one by one according
to the priority assigned to the ports, and if any device requires service, then it
provides it.
 In interrupt, when the device requires service, it sends the request to
microcontroller and the controller then provides service to it.
 Which register is used for serial programming in 8051 microcontroller?
(AU AM 2015)
 The SCON register is used for serial programming in 8051. It is an 8-bit register used
to program the start bit, stop bit, and data bits of data framing, among other things.
 SMO and SM1 are D7 and D6 of the SCON register, respectively. These two bits
determine the framing of data by specifying the number of bits per character, and
the start and stop bits. They take the following combinations.
SM0 SM1 Description
0 0 Serial mode 0
0 1 Serial mode 1, 8-bit data, 1 stop bit ,
1 start bit
1 0 Serial mode 2
1 1 Serial mode 2

 What is PWM? (AU ND 2014 -2)
 A modulation technique that uses a digital circuit to create a variable analog signal
PWM is a simple concept open and close a switch at uniform repeatable intervals.
 For a given fixed load to maintain a steady speed by using pulse width modulation.
 By changing the width of the pulse applied to the DC motor we can increase or
decrease the amount of power provided to the motor, thereby increasing or
decreasing the motor speed.
 Give the schematic to interface a relay with microcontroller? (AU ND 2014)
 The schematic to interface a relay with microcontroller is:
 Write about the design steps involved in using microcontroller for stepper motor.
(AU AM 2014)
 Motor has two phases, with center-tap winding. The center taps of these windings are
connected to the 12V supply. Due to this, motor can be excited by grounding four
terminals of the two windings.
 Motor can be rotated in steps by giving proper excitation sequence of these windings.
 The lower nibble of port A of the 8255 is used to generate excitation signals in the
proper sequence.
 Microcontroller is programmed to rotate the stepper motor.
 State the importance of relay coil. (AU AM 2013)
 A relay is usually an electromechanical device that is actuated by an electrical current.
The current flowing in one circuit causes the opening or closing of another circuit.
 Relays are like remote control switches and are used in many applications because of
their relative simplicity, long life, and proven high reliability.
 Relays are used in a wide variety of applications throughout industry, such as in
telephone exchanges, digital computers and automation systems
 All relays contain a sensing unit, the electric coil, which is powered by AC or DC current.
 Why the relays are called electromagnetic relays? (AU ND 2013)
 An iron core is surrounded by a control coil. As shown, the power source is given to the
electromagnet through a control switch and through contacts to the load.
 When current starts flowing through the control coil, the electromagnet starts
energizing and thus intensifies the magnetic field. Thus the upper contact arm starts to
be attracted to the lower fixed arm and thus closes the contacts causing a short circuit
for the power to the load.
 On the other hand, if the relay was already de-energized when the contacts were closed,
then the contact move oppositely and make an open circuit.

 Write an ALP to receive input from port P1.5 and if it is high then an output 35H is
sent to Port 0. (AU AM 2013)
L1: JNB P1.5, L1 ; Jump if no bit P1.5 is set
MOV A, #35H; Move 35H to Accumulator
MOV P0, A ; Move the Contents of Accumulator to Port P0
 What is meant by I2C standard? (AU AM 2012)
In I2C only two bi-directional lines Serial Data (SDA) & Serial Clock (SCL) are required to
carry information between the devices connected to the bus. Each I2C device is recognized
by a unique 7-bit address.
The device that initiates the communication is called MASTER. The master controls the
clock signal. Whereas the device being addressed by the Master is called as SLAVE.
Generation of clock signals on the I2C-bus is always the responsibility of master devices;
each master generates its own clock signals when transferring data on the bus.
 What are precautions required while interfacing microprocessor with motors?
(AU AM 2012)
While interfacing microprocessor with motors, the following precautions are made:
 Care should be taken to assure lifting in the direction intended in the design of the
lifting means.
 Data lines for microprocessor should be connected to the data lines of the Interfacing a
device which is connected to the motor.
 Why do we need relay interface? What is SPDT relay? (AU ND 2011)
 Relay interface allows the isolation of two separate section of a system with two
different voltage sources.
 SPDT relay is a single pole double throw relay.
 What are the sources of interrupts in 8051? (AU ND 2010)
In general, the five sources of interrupts in 8051are:
 Timer 0 overflow interrupt - TF0, Timer 1 overflow interrupt - TF1
 External hardware interrupt - INT0,INT1
 Serial communication interrupt - RI/TI
 The timer and serial interrupts are internally generated by the microcontroller.
 External interrupts are generated by additional interfacing devices or switches that are
externally connected to the microcontroller. These external interrupts can be edge
triggered or level triggered.
 How is the microcontroller used for the traffic light control application?
(AU ND 2010)
 When the power is applied to the circuit microcontroller initializes its ports for driver,
status LED indicator timer on/off switch jumpers for variable pass time and enters in
infinite loop where it checks for the timer on/off switch.
 If it is enabled, timer is on and signal lamps switches in sequence if the timer is not
enabled all the roads are cleared.
 Every time, it checks for the jumper to determine the pass time for vehicles.
 List the applications of Microcontroller. (AU AM 2008)
The applications of microcontroller are listed below:
 Light sensing & controlling devices
 Temperature sensing and controlling devices
 Fire detection & safety devices
 Industrial instrumentation devices
 Process control devices

 What is the function of SM2 bit in the SCON register of 8051? (AU ND 2007)
 SM2 is a flag for "Multiprocessor communication." Generally, whenever a byte has been
received the 8051 will set the "RI" (Receive Interrupt) flag. This lets the program know
that a byte has been received and that it needs to be processed.
 However, when SM2 is set the "RI" flag will only be triggered if the 9th bit received was a
"1". That is to say, if SM2 is set and a byte is received whose 9th bit is clear, the RI flag
will never be set. This can be useful in certain advanced serial applications.
 Give some example of input devices to microprocessor-based systems.
The input devices used in the microprocessor- based system are:
 Keyboards
 DIP switches
 ADC
 Floppy disc, etc.
 What are the functions performed by 8279?
Hence the following are the functions are performed by 8279
 Key board scanning
 Key code generation and
 Display refreshing
 Draw the TCON Register Format.
TCON is bit addressable. The address of TCON is 88H. It is partly related to Timer and partly
to interrupt.
TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0
TCON Register Format
 TF1: Timer1 overflow flag. It is set when timer rolls from all 1s to 0s. It is cleared when
processor vectors to execute ISR located at address 001BH.
 TR1: Timer1 run control bit. Set to 1 to start the timer / counter.
 TF0: Timer0 overflow flag. (Similar to TF1)
 TR0: Timer0 run control bit.
 IE1: Interrupt1 edge flag. Set by hardware when an external interrupt edge is detected.
It is cleared when interrupt is processed.
 IE0: Interrupt0 edge flag. (Similar to IE1)
 IT1: Interrupt1 type control bit. Set/ cleared by software to specify falling edge / low
level triggered external interrupt.
 IT0: Interrupt0 type control bit. (Similar to IT1)
 What is the use of a watch dog timer?
 A watching timer is used to protect an application in case the controlling
microcontroller begins to run amok and execute randomly rather than the
preprogrammed instructions written for the application.
 Explain synchronous data transmission.
 In synchronous mode (mode 0), the instruction clock is used.
 Data transfer is initiated by writing to the serial data port address.
 Txd pin is used for clock output, while Rxd pin is for data transfer.
 When a character is received, the status of the data transfer is monitored by polling the
RI-n bit in serial control register (SCON).

PART B
1. Write and explain. What is known as Serial Port Programming? (13)(AU ND 2018)
2. What are sensor interfacing and external memory interfacing? Explain. (13)(AU ND 2018)
3. Draw and explain the block diagram of alarm controller. (13)(AU AM 2018)
4. (i)Interface the ADC converter with 8051 and explain with neat diagram.
(07)(AU ND 2017)
(ii)Write the assembly language program to execute the ADC conversion.
(06)(AU ND 2017)
5. Write a program for generation of unipolar square waveform of 1 kHz frequency using
Timer0 in mode0. Consider the system frequency as 12 MHz. (13)( AU AM 2017)
6. Demonstrate the interfacing of the stepper motor with 8051 and explain its interfacing
diagram and develop program to rotate the motor in clock wise direction.
(16)( AU ND 2017-6)
7. Explain 8051 serial port programming with examples. (16) ( AU AM 2016)
11.(i) Explain stepper motor control using 8051 microcontroller. (08) ( AU ND 2014)
(ii) Explain in detail about the interrupt programming in 8051 (08)
8. (i) Explain in detail about 8051 serial port. (08) (AU AM 2013)
(ii) Explain how an LCD is interfaced with 8051. (08)
9. (i) Explain the interfacing of 4 x 4 matrix keyboard with 8051
microcontroller. (10) (AU MJ 2013)
(ii) Write shortly on the various operating modes for serial port
of 8051. (06)
10. Explain the interfacing of keyboard with 8015 microcontroller. (16) (AU ND 2013)
11. Write a program for counter 1 in mode 2 to count the pulses and display the state of
TL1Count on PORT 2. Assume that clock input is connected to T1 pin (P 3.5).
(16) (AU ND 2012)
12. Describe in detail the microcontroller based system design with an Example.
(16) (AU ND 2012)
13. List any four application of stepper motor? Explain how to interface stepper motor with µc.
(16) (AU ND 2011)
14. What is the need for PWM in motor control application? Explain. (16) (AU ND 2011)
15. With a neat functional diagram show how an 8051 microcontroller is in controlling a
stepper motor. (16) (AU AM 2010)
16. Explain the different jump instructions in 8051. (16) (AU AM 2010)
17. Discuss timers of 8051 microcontroller. (16) (AU ND 2010)
PART C
1. Write an assembly language program using 8051 instructions to arrange an array of
numbers in ascending order. (15) (AU AM 2010) 5
2. With diagram explain the interfacing of a stepper motor with a 8051 microcontroller and
write an 8051 ALP to run the stepper motor in both forward and reverse direction with
delay. (15) (AU AM 2011)
3. (i)Describe the different modes of operation of timer/counters in 8051 with its associated
register. (15) ( AU AM 2015)
(ii)How does one interface a 16 x 2 LCD display using 8051 microcontroller?
4. Describe the different modes of operation of timer/counters in 8051 with its associated
register. (15) ( AU ND 2016-2)
5. Illustrate the serial communication in 8051, with its special function register.
(15)(AU ND 2017)

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