Advanced Microprocessor 1

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Short Answers

1. Define Microprocessor?
Microprocessor is a multipurpose, programmable, clock-driven, register
based electronic 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 as output.
2. What is Hardware and Software?
The physical components of the system i.e. computer are called
Hardware. Group of programs is called software.
3. Why the microprocessor is viewed as a programmable Device?
Microprocessor is programmable because it can be instructed to perform
given tasks within its capability. Microprocessor is designed to understand
and execute many binary instructions.
4. What is Central processing Unit ( CPU ) ? And Write the use of it.
CPU is a heart of the computer. Central processing Unit controls the
operation of the computer. In a microcomputer the CPU is a
microprocessor. The CPU fetches binary coded instructions from memory,
decodes the instructions into a series of simple actions and carries out these
actions in a sequence of steps.
5. What is a chip?
A chip is also called an integrated circuit. Generally it is a small, thin piece
of silicon onto which the transistors making up the microprocessor have
been etched. A chip might be as large as an inch on a side and can contain
tens of millions of transistors. Simpler processors might consist of a few
thousand transistors etched onto a chip just a few millimeters square.
6. What is mini computer?
Scaled down versions of mainframe computers are often called
minicomputers. The main unit of a minicomputer usually fits in a single
rack or box. A mini computer runs more slowly, works directly with smaller
data words and does not have as much memory as mainframe. computers of
this type are used for business data processing, industrial control and
scientific research
7. What is System Bus?
The System bus is a communication path between the microprocessor and
peripherals. It is nothing but a group of wires to carry bits.

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8. What is Address Bus?

The address bus consists of 16, 20, 24 or 32 parallel signal lines. On these
lines the CPU sends out the address of the memory location that is to be
written to or read from. The number of memory locations that the CPU
can address is determined by the number of address lines. If the CPU has
N address lines, then it can directly address 2N memory locations. Simply,
we can say that Address Bus is used to carry the address.
9. What is Data Bus?
The data bus consists of 8, 16, or 32 parallel signal lines. The data bus
lines are bidirectional. This means that the CPU can read data in from
memory or from a port on these lines, or it can send data out to memory or
to a port on these lines. Simply we can say that data bus is used to carry
the data .
10. What is Assembly Language?
A medium of communication with a computer in which programs are
written in mnemonics. Binary instructions are given abbreviated names
called mnemonics, which form the assembly language for a given
processor.
11. What is Machine Language?
The binary medium of communication with a computer through a designed
set of instructions specific to each computer.
12. Define Embedded Systems:
Embedded systems are those used to control specialized hardware in which
the computer system is installed.
Microprocessor is the final product and is not available for reprogramming
to the end user. E.g. Copying machine
13. What is microcontroller?
Microcontroller is a Device that includes microprocessor, memory and I/O
signal lines on a single chip, fabricated using VLSI technology.

14. What do you mean ‘ Data Width’?

Data Width is the width of the ALU. An 16 bit ALU can add / subtract/
multiply etc.. two 16 bit numbers . In many cases, the external data bus
is the same width as the ALU, but not always. The 8088 has a 16 bit
ALU and 8 bit bus , while the modern Pentiums fetch data 64 bits at a
time for their 32 bit ALUs.

15. What is compiler?

Compiler is a program that translates English like words of a high level
language into the machine language of a computer. A compiler read a
given program ,called a source code, in its entirely and then translates
the program into the machine language, which is called an Object Code.

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16. List the four operations commonly performed by MPU( Micro

processing Unit)?
Memory Read : Reads data (or instructions) from memory.
Memory Write: Writes Data (or instructions) into memory.
I/O Read: Accepts data from input devices.
I/O Write: Sends data to output devices.

17. Define Register Relative Addressing Mode.

Register Relative Addressing Mode : The Effective Address is
Calculated by the sum of 8- or 16 bit displacement and the contents of a base
Register or an index Register.
E.A. = content of(BX or BP or SI or DI) + (8 bit displacement (sign
extended ) or 16 bit displacement
Physical Address = E.A +(DS)*1610
18. Define Immediate Addressing.
An 8 bit or 16 bit immediate data follows the instruction. For e.g
MOV AX,5020H instruction transfers a word 5020H to the AX register .

19. Define Direct Addressing mode :

A 16 bit offset address of the data memory location is specified
with reference to the DS segment starting address.
For.E.g MOV [1020H],5020H instruction transfers a word 5020H to the data
memory location at 11020H if DS=1000H.

20. Define Relative based indexed addressing mode:

Relative Based Indexed Addressing Mode : Effective Address is calculated by

the sum of 8- or 16 bit displacement and a based indexed address.
E.A.= (BX or BP) + (SI or DI) +( 8 bit displacement (sign extended ) or 16
bit displacement)
Physical Address= E.A + (DS)*1610
21. List the branch related addressing mode:
Intra segment Direct
Intra segment Indirect
Inter segment Direct
Inter Segment Indirect

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22. List the functions of Bus Interface Unit in 8086.

Sends out addresses
Fetches instructions from memory
Reads data from ports and memory
Writes data to port and memory
23. Write any two advantages of segment registers in 8086
a. It allows the memory capacity to be 1MB even though the address
associated with individual instructions are 16 bits wide.
b. It allows the instruction,data, or stack portion of a program to be more
than 64KB long by using more than one code, data, or stack segment
24. What is the use of Instruction pointer in 8086 ?
Instruction pointer holds the 16 bit address of the next code byte within
the code segment. The value contained in the IP is called effective address or
offset. It contains the distance from the base address to the next instruction
byte to be fetched.
25. Write about the auxiliary carry flag used in 8086 ?
It is set if there is a carry out of bit 3 during an addition or a borrow by
bit 3 during a subtraction. This flag is used exclusively for BCD
arithmetic.
26. When the Overflow flag is set ?
For addition of 16 bits, this flag is set when there is a carry into the
MSB and no carry out of the MSB.
27. Define Register addressing mode:
Datum is in the register that is specified by the instruction
E.g : MOV CX,AX (16 bit operand)
MOV CL,AL ( 8 bit operand)
28. Define Register Indirect Addressing mode:
Effective address of the datum is in the base register BX or an index
register that is specified by the instruction.

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29. Define Register relative addressing mode:

The effective address is the sum of an 8- or 16 bit displacement and the
contents of a base register or an index register.
30. Define Based Indexed addressing mode:
The effective address is the sum of a base register and an index register ,
both of which are specified by the instruction.It is also called as Base
related Indexed addressing.
31. Define Intra segment direct addressing mode:
The effective branch address is the sum of an 8- or 16 bit displacement
and the current contents of IP.
32. Define Intra segment Indirect addressing mode:
The effective branch address is the contents of a register or memory
location that is accessed using any of the data related addressing modes
except the immediate mode. The contents of IP are replaced by the effective
branch address.
33. Define Inter segment addressing mode:
It replaces the contents of IP with part of the instruction and the contents
of CS with another part of the instruction.
34. Define Inter segment Indirect addressing mode:
It replaces the contents of IP and CS with the contents of two
consecutive words in memory that are referenced by using any of the
data related addressing modes except immediate and register modes.
35. What is the use of PUSHF instruction used in 8086 ?
It pushes the flag register contents to the top of the stack. No flags are
affected.
36. Define XLAT instruction used in 8086.
It translates a byte in AL using a table in memory. The offset address is
calculated by adding the 8 bit contents of the AL register and the
contents of BX register. BX register contains the starting offset address
of the Lookup table . After execution , corresponding data memory
contents of the lookup table are loaded into the AL register.

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37. What is the use of ‘W’ bit in opcode ?.

W bit in op-code : If an instruction in 8086 can operate on either a byte or a
word , the op-code includes a W-bit which indicates whether a byte ( W =0 )
or a word (W =1) is being accessed.
38. What is DAS instruction ?
DAS : Decimal Adjust After Subtraction
This instruction converts the binary result of a SUB or SBB instructi
on in AL to Packed BCD format. It operates only on AL Register.
39. What is Packed BCD Format ?
Packed BCD Format : Packed BCD Numbers are stored in two digits to a
byte , in 4 bit groups referred to as nibbles. ALU is capable of performing
only binary addition and subtraction , but by adjusting the sum or difference
the correct result in packed BCD format.
40. What is the value of ‘AX’ after executing following instructions.
MOV AH,00
MOV AL,’7’
ADD AL,’3’
AAA

Ans : AX= 0100 H

41. What is difference between DIV and IDIV instruction in 8086 ?
DIV : It operates only on unsigned number.
IDIV : It operates only on signed numbers.
42. Write about the following instruction : MOV CS:[BX], DL

MOV CS:[BX],DL - It copies a byte from DL Register. Effective Address for

the memory location is contained in the BX Register. Normally an effective
address in BX will be added to the data segment base in DS to produce the
physical memory address. In this instruction CS: indicates that we want the
BIU to add the effective address to the code segment base in CS to produce
the physical address.

content of(BX+(CS) * 1610) = (DL)

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43. What is Programmed I/O ?

Programmed I/O : It consists of continually examining the status of an
Interface and performing an I/O operation with the Interface when its status
indicates that it has data to be input or its data- out buffer register is ready to
receive data from the CPU.
44. What is the use of Directives in 8086 ?
Directives in 8086 give directions to the assembler during the assembly
process but are not translated into machine instruction.
45. What is AAS instruction in 8086 ?
AAS : Adjust Result of ASCII Subtraction
This instruction adjust the binary result of SUB or SBB instruction.
46. What is Unpacked BCD Format ?
Unpacked BCD Format : In Unpacked BCD, there is only one digit per byte
and because of this,unpacked multiplication and division can be done. Binary
operations act on signle bytes and the results are adjusted. For Division , the
adjustment is done before the binary division.
47. What is the value of AL after executing the following instructions.
MOV AL,35H
ADD AL,49H
DAA

Ans : AL= 84
48. Define Segment Override Prefix.
Segment Override Prefix : To permit exceptions to the Segment Register
usage, a special one byte instruction called a segment override prefix is
available . It is of the form :
XXX XX XXX
Mod REG R/M

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49. Write the difference between CBW and CWD instruction in 8086.

CBW : Convert a byte to a word, sign extend AL Register into a AH

Register.
CWD : Convert a word to a double word ,sign extend the AX Register into
the DX Register.
50. Write about the following instruction : LES CX, [3483H]
Copy the contents of memory at the displacement of 3483H in
DS to CL, contents of 3484H in DS to CH, and copy the contents of
memory at displacement of 3485H and 3486H in DS to ES Register.
51. What is the use of D bit in opcode?
D bit: It is used in double operand instruction. It is used to indicate
whether the register specified by REG is the source operand (D=0) or the
destination operand (D=1).

52. What is the use of V bit in opcode ?

It is used by shift and rotate instructions to determine the number
of shifts. V bit is set to 0 if the shift count is to be 1. V bit is set to 1 if the CL
register contains the shift count.

53. Write the use of Z bit in opcode?

It is used by REP instruction. Z bit helps to control the loop. It will
be repeated the number of items indicated by the CX register or until Z bit dose not
match the Zero flag whichever occurs first.

54. How the execution time of an instruction is calculated?

Execution time of an instruction can be determined by
multiplying the number of clock pulses needed to execute the instruction by the
clock period.
55. Define EQU directive in 8086 assembly language?
It is used to assign a name to constants used in the programs.
Consider the statement ‘corr EQU 07H’ , this would tell the assembler to insert
the value 07H everytime that it finds the name corr in the program statement.
56. Write the use of Assume directive in 8086 assembly language using one
example?
Assume CS: code_here, DS:data_here
It tells the assembler that the logical segment code_here contains
the instruction statements for the program and should be treated as a code segment.
It also tells the assembler that it should treat the logical segment data_here as the
data segment for this program.

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57. Define EXTRN directive in in 8086 assembly language?

The EXTRN directive is used to inform the assembler that the
names or labels following the directive are in some other assembly module.
58. What is Emulator?
Emulator is a mixture of hardware and software .It is used to test
and debug the hardware and software of an external system such as the prototype
of a microprocessor based instrument.

59. What is the use of TEST instruction in 8086?

Test instruction is the same as the AND instruction except that ite does
not put the result anywhere. Like the CMP instruction , it is used only to
set the flags.
60. Define LAHF and SAHF instructions in 8086.
LAHF : Load the 8085 equivalent flags into the AH register.
SAHF: Store the AH register into the low order byte of the flag register.

61. While handling the interrupt instructions in 8086, What are the internal
operations may be carried out by the stack?

(i)SP =SP-2 , stack ß Push flag reg. Contents, IF =0 , TF =0

(ii) SP=SP-2, Stackß CS Reg. Contents, Address of Interrupt pointer =
Interrupt type * 4 , CS Register Contents ß Second word of Interrupt pointer
(iii) SP=SP-2, Stackß IP, IPß First word of Interrupt pointer

62. Write an ALP program in 8086 to add two 16 bit numbers.

MOV AX,1236H
MOV BX,8765H
ADD AX,BX
HLT

63. Write about EVEN directive in 8086 ALP.

It forces the address of the next byte to be even. 8086 words can be accessed
in less time if they begin at even address.

64. Write about the following instruction :

Call WORD PTR [BX]
Offset of the first instruction of procedure is in two memory addresses in
DS. It replaces the contents of IP with contents of word memory locations
in DS pointed to by BX.

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65. Write an ALP program in 8086 to subtract numbers.

MOV AX,1236H
MOV BX,8765H
SUB AX,BX
HLT
66. When the 8086 processor is in minimum mode?
___
The processor 8086 is in minimum mode when its MN/MX pin is
strapped to +5 V
67. When the 8086 processor is in maximum mode?
___
The processor 8086 is in maximum mode when its MN/MX pin is
grounded.
68. Define latch.
A bistable circuit that is set and reset by appropriate input signals .
An electronic circuit that records the status of a signal until it is reset.
69. Define clock pulse.
A synchronization signal provided by a clock . A periodic signal
used for synchronization and for measuring intervals of time.
70. What is the use of s1 , s2 ,s3 signals when 8086 is in maximum mode?
It indicates the type of transfer to take place during the current bus
cycle.
71. Define Machine cycle.
A group of states required for a basic bus operation is called a machine cycle.

72. Write any three differences between 8086 and 8088?

a. 8086 – 20 address lines , 16 data lines
8088 – 20 address lines, 8 data lines
__
b. ( Maximum Mode) 8086 – M/IO
__
8088 – IO/M
c. 8086 uses a maximum supply current of 360 mA
8088 uses a maximum supply of 340mA

73. Define Instruction cycle?

The total time takes the 8086 to fetch an instruction is called an instruction
cycle. Instruction cycle consists of one or more machine cycles. Each
machine cycle is made up of states.
74. What is polling?

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In programmed I/O , testing of ready bits or signals is known as

polling.
75. Define Interrupt I/O?
Interrupt is an event that causes the CPU to initiate a fixed
sequence known as an interrupt sequence.
76. What do you mean by wait states in system bus timing?
Wait states are inserted between T3 and T4, when a memory or I/O
interface is not able to quickly enough during a transfer.
77. What is block transfer?
To execute a sequence of instructions that causes a special system
component associated with the interface to transfer a sequence of bytes or words to
or from a predesignated block of memory locations . It is called a block transfer.
78. Define Stop bit.
Bit or group of bits that identifies the end of a data word and
defines the space between data words. Bit indicating the end of an asynchronous
serial transmission.
79. Define Baud Rate:
The data rate can be expressed as bits/sec or characters/sec . The
term bits/sec is called baud rate.
80. Define Modem.
Acronym for modulator/Demodulator. A device that translates
digital pulses from a computer into analog signals for telephone transmission and
analog signals from the telephone into digital pulses the computer can understand.

81. Define synchronous Communication.

It means regular time relationship. Pertaining two or more processes that
depend upon the occurence of specific events such as common timing
signals.
82. What is overrun error ?
Loss of data because a receiving device is unable to accept data at the
rate it is transmitted.
83. What is the use of ADSTB signal in 8237?
ADSTB is Address Strobe. Same as address latch enable signal. It is
used by DMA controller to latch the address bits A15-A8 during DMA
transfer.

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84. What is the use of Current Byte count register?

It programs a channel for the number of bytes transferred during a DMA
action. The number loaded into this register is one less than the number
of bytes transferred.

85. Define Asynchronous Communication.

Without regular time relationship. Transmission of a character or a
block of characters can begin at any time , but in which the bits that represent the
character or block have equal time duration.
86. Write about 80486 processor?
It is an enhanced version of 80386. It executes instructions in one
clocking period. It also contains 8k byte cache memory. Pentium and Pentium pro
also contain improved numeric co-processors that operate 5 times faster than
80486 numeric co-processor.
87. What is the difference between 80186 and 80188?
Difference between these two is width of their data buses. 80186
has 16 bit data bus and 80188 has 8 bit data bus.

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