Microprocessor
Lab Viva Questions with Answers
1.What is a Microprocessor?
Microprocessor is a CPU
fabricated on a single chip, program-controlled device, which fetches the
instructions from memory, decodes and executes the instructions.
2. What is Instruction Set?
It is the set of the instructions that the
Microprocessor can execute.
3. What is Bandwidth ?
The number of bits processed by the processor
in a single instruction.
4. What is Clock Speed ?
Clock speed is measured in the
MHz and it determines that how many instructions a processor can processed. The
speed of the microprocessor is measured in the MHz or GHz.
5. What are the features of Intel 8086 ?
Features:
· Released by Intel in 1978
· Produced from 1978 to 1990s
· A 16-bit microprocessor chip.
· Max. CPU clock rate:5 MHz to 10
MHz
· Instruction set: x86-16
· Package: 40 pin DIP
· 16-bit Arithmetic Logic Unit
· 16-bit data bus (8088 has 8-bit data bus)
· 20-bit address bus - 220 =
1,048,576 = 1 meg
· The address refers to a byte in
memory.
· In the 8088, these bytes come in
on the 8-bit data bus. In the 8086,
bytes at even addresses come in on the low half of the data bus (bits 0-7) and
bytes at odd addresses come in on the upper
half of the data bus (bits 8-15).
· The 8086 can read a 16-bit word
at an even address in one operation and at an odd address in two
operations. The 8088 needs two
operations in either case.
· The least significant byte of a
word on an 8086 family microprocessor is at the
lower address.
6. What is Logical Address:?
• A memory address on the 8086 consists
of two numbers, usually written in hexadecimal and separated by a colon,
representing the segment and the offset. This combination of segment and offset
is referred to as a logical address
• Logical address=segment: offset
7. What is The Effective Address:
• In general, memory accesses take the
form of the following example:
• Mov ax, [baseReg + indexReg +
constant]
• This example copies a word sized value
into the register AX.
• Combined, the three parameters in
brackets determine what is called the effective address, which is simply the
offset referenced by the instruction
8. What is Physical Address?
Physical memory address pointed
by SEGMENT:OFFSET pair is calculated as:
Physical address = (<Segment
Addr> * 10) + <Offset Addr>
9.What are the flags in 8086?
In 8086 Carry flag, Parity flag,
Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag,
Direction flag, and Sign flag.
10.Why crystal is a preferred clock source?
Because of high stability, large
Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal
is used as a clock source most of the times.
11.What is Tri-state logic?
Three Logic Levels are used and
they are High, Low, High impedance state. The high and low are normal logic
levels & high impedance state is electrical open circuit conditions.
Tri-state logic has a third line called enable line.
12.What happens when HLT instruction is executed in processor?
The Micro Processor enters into
Halt-State and the buses are tri-stated.
13.What is Program counter?
Program counter holds the address
of either the first byte of the next instruction to be fetched for execution or
the address of the next byte of a multi byte instruction, which has not been
completely fetched. In both the cases it gets incremented automatically one by
one as the instruction bytes get fetched. Also Program register keeps the
address of the next instruction.
14. What is 1st / 2nd / 3rd / 4th generation processor?
The processor made of PMOS / NMOS
/ HMOS / HCMOS technology is called 1st / 2nd / 3rd / 4th generation processor,
and it is made up of 4 / 8 / 16 / 32 bits.
15.Name the processor lines of two major manufacturers?
High-end: Intel - Pentium (II,
III, 4), AMD - Athlon. Low-end: Intel - Celeron, AMD - Duron. 64-bit: Intel -
Itanium 2, AMD - Opteron.
16.How many bit combinations are there in a byte?
Byte contains 8 combinations of
bits.
17.Have you studied buses? What types?
There are three types of buses.
Address bus: This is used to
carry the Address to the memory to fetch either Instruction or Data.
Data bus : This is used to carry
the Data from the memory.
Control bus : This is used to
carry the Control signals like RD/WR, Select etc.
18.What is the Maximum clock frequency in 8086?
5 Mhz is the Maximum clock
frequency in 8086.
19.What is meant by Maskable interrupts?
An interrupt that can be turned
off by the programmer is known as Maskable interrupt.
20.What is Non-Maskable interrupts?
An interrupt which can be never
be turned off (ie. disabled) is known as Non-Maskable interrupt
21.What are the different functional units in 8086?
Bus Interface Unit and Execution
unit, are the two different functional units in 8086.
22.What are the various segment registers in 8086?
Code, Data, Stack, Extra Segment
registers in 8086.
23.What does EU do?
Execution Unit receives program
instruction codes and data from BIU, executes these instructions and store the
result in general registers.
24.Which Stack is used in 8086? k is used in 8086?
FIFO (First In First Out) stack
is used in 8086.In this type of Stack the first stored information is retrieved
first.
25.What are the flags in 8086?
In 8086 Carry flag, Parity flag,
Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag,
Direction flag, and Sign flag.
26.What is SIM and RIM instructions?
SIM is Set Interrupt Mask. Used
to mask the hardware interrupts.
RIM is Read Interrupt Mask. Used
to check whether the interrupt is Masked or not.
27.What are the different types of Addressing Modes?
A:- There are 12 different types
of Addressing Modes.They are:-
<1> Immediate:-The
Immediate data is a part of instruction, and appears in the form of successive
bytes.
<2> Direct:-A 16-bit memory
address(offset) is directly specified in the instruction as a part of it.
<3> Register:-Data is
stored in a register and it is referred using the particular register (except
IP).
<4> Register Indirect:-The
address of the memory location which contains data or operand is determined in
an indirect way.
<5> Indexed:-offset of the
operand is stored in one of the index registers.
<6> Register Relative:-The
data is available at an eefective address formed by adding an 8-bit or 16-bit
displacement with the content of any one of the registers BX,BP,SI and DI in
the default (either DS or ES) segment.
<7> Based Indexed:-The
effective address of the data is formed,in this addressing mode,by adding content
of a base register to the content of an index register.
<8> Relative Based
Indexed:- The effective address is formed by adding an 8 or 16-bit displacement
with the sum of contents of any one of the base registers and any one of the
index registers,in the default segment.
<9> Intrasegment Direct
Mode:-In this mode,the address to which the control is to bve transferred lies
in the segment in which the control transfer instruction lies and appears
directly in the instruction as an immediate displacement value.
<10> Intrasegment Indirect
Mode:-In this mode,the displacement to which the control is to be
transferred,is in the same segment in whgich the control transfer instruction
lies,but it is passed to the instruction indirectly.
<11> Intersegment
Direct:-In this mode,the address to which the control is to be transferred is
in a different segment.
<12> Intersegment
Indirect:-In this mode,the address to which the control is to be transferred
lies in a different segment and it is passed to the instruction indirectly
sequentially.
28.What are the General Data Registers & their uses?
A:- The Registers AX,BX,CX,DX are
the general Purpose 16-bit registers.AX register as 16-bit accumulator.BX
register is used as an offset Storage.CX register is used as default or implied
counter.Dx register is used as an implicit operand or destination in case of a
few instructions.
29.What are Segment Registers & their uses?
A:-There are 4 Segment Registers
Code Segment(CS),Data Segment(DS),Extra Segment(ES) & Stack Segment(SS)
registers.CS is used for addressing memory locationin code.DS is used to points
the data.ES refers to a segment which is essentially in another data segment.SS
is used fopr addressing stack segment of memory.
30.What are Flag registers?
A:-Divided into 2
parts:-Condition code or status flags and machine control flags.
S-Sign Flag:-Is to set when the
result of any computation is negative.
Z-Zero Flag:-Is to set if the
result of the computation or comparision performed by the previous instruction
is zero.
C-Carry Flag:-Is set when there
is carry out of MSB in case of addition or a borrow in case of subtraction.
T-Trap Flag:-Is set,the processor
enters the single step execution mode.
I-Interrupt Flag:-Is set,the
maskable interrupts are recognised by the CPU.
D-Direction Flag:-Is set for
autoincrementing or autodecrementing mode in string manipulation instructions.
AC-Auxiliary Carry Flag:-Is set
if there is a carry from the lowest nibble during addition or borrow for the
lowest nibble.
O-Overflow Flag:-Is setif the
result of a signed operation is large enough to be accommodated in a
destination register.
31.What does the 8086 Architecture contain?
A:-The complete architecture of
8086 can be divided into 2types :-Bus Interface Unit(BIU) & Execution Unit.
The BIU contains the circuit for
physical address calculations and a precoding instruction byte queue & it
makes the bus signals available for external interfacing of the devices.
The EU contains the register set
of 8086 except segment registers and IP.It has a 16-bit ALU,able to perform arithmetic
and Logic operations.
32) What are Data Copy/Transfer Instructions?
A:- Mov, Push, Pop, Xchg, In, Out, Xlat, Lea, Lds/Les,
Lahf, Sahf, Pushf, Popf
33. What are Machine Control Instructions?
A:- Nop, Hlt, Wait, Lock
34) What are Flag Manipulation Instructions?
A:- Cld, Std, Cli, Sti
35) What are String Instructions?
A:- Rep, MovSB/MovSW, Cmps, Scas, Lods, Stos
36) What are different parts for 8086 architecture?
A:- The complete architecture of
8086 can be divided into 2types :-Bus Interface Unit(BIU) & Execution Unit.
The BIU contains the circuit for
physical address calculations and a precoding instruction byte queue & it
makes the bus signals available for external interfacing of the devices.
The EU contains the register set
of 8086 except segment registers and IP.It has a 16-bit ALU,able to perform
arithmetic and Logic operations.
37.What is an Interrupts
Def:- An interrupt operation
suspends execution of a program so that the system can take special action.The
interrupt routine executes and normally returns control to the interrupted
procedure, which then resumes execution.BIOS handles Int 00H-1FH, whereas DOS
handles INT 20H-3FH.
38. What is an Opcode?
A:-The part of the instruction
that specifies the operation to be performed is called the Operation code or Op
code.
39.What is an Operand?
A:-The data on which the
operation is to be performed is called as an Operand.
40.Explain the difference between a JMP and CALL instruction?
A:-A JMP instruction permantely
changes the program counter.
A CALL instruction leaves
information on the stack so that the original program execution sequence can be
resumed.
41.What is meant by Polling?
A:- Polling or device Polling is
a process which idenfies the device that has interrupted the microprocessor.
42.What is meant by Interrupt?
A:-Interrupt is an external
signal that causes a microprocessor to jump to a specific subroutine.
43.What is an Instruction?
A:-An instruction is a binary
pattern enetered through an input device to command the microprocessor to
perform that specific function.
44.What is Microcontroller and Microcomputer?
A:- Microcontroller is a device
that includes microprocessor:memory and I/O signal lines on a single
chip,fabricated using VLSI technology.
Microcomputer is a computer that
is designed using microprocessor as its CPU.It includes microprocessor,memory
and I/O.
45.What is Assembler?
A:-The assembler translates the
assembly language program text which is given as input to the assembler to
their binary equivalents known as object code.
The time required to translate
the assembly code to object code is called access time.The assembler checks for
syntax errors&displays them before giving the object code.
46.Define Variable?
A:-A Variable is an identifier
that is associated with the first byte of data item.
47.Explain Dup?
A:-The DUP directive can be used
to initialize several location & to assign values to these locations.
48.Define Pipelining?
A:-In 8086,to speedup the
execution program,the instructions fetching and execution of instructions are
overlapped each other.this is known as Pipelining.
49.What is the use of HLDA?
A:-HLDA is the acknowledgment
signal for HOLD. It indicates whether the HOLD signal is received or not.
HOLD and HLDA are used as the
control signals for DMA operations.
50. Explain about "LEA"?
A:-LEA(Load Effective Address) is
used for initializing a register with an offset address.
A common use for LEA is to
intialize an offset in BX, DI or SI for indexing an address in memory.
An equivalent operation to LEA is
MOV with the OFFSET operator, which generates slightly shorter machine code.
51. Difference between "Shift" and "Rotate".
A:-Shift and Rotate commands are
used to convert a number to another form where some bits are shifted or
rotated.
A rotate instruction is a closed
loop instruction.That is,the data moved out at one end is put back in at the
other end.
The shift instruction loses the
data that is moved out of the last bit locations.
Basic difference between shift
and rotate is shift command makes "fall of " bits at the end of the
register.
Where rotate command makes
"wrap around" at the end of the register.
52. Explain about .MODEL SMALL?
A:- .MODEL directive:-This
simplified segment directive creates default segments and the required ASSUME
and GROUP statements.
Its format is .MODEL
memory-model.The following are the memry models
Tiny:-Code and data in one
segment, for .COM programs.
Small:-Code in one segment
(<=64K), data in one segment (<=64K). It generates 16-bit offset
addresses.
Medium:-Any number of code
segments, data in one segment (<=64K).
Compact:-Code in one segment
(<=64K), any number of data segments. It generates 32-bit adresses, which
require more time for execution.
Large:-Code and data both in any
number of segments, no array >64K.
Huge:-Code and data both in any
number of segments, arrays may be >64K.
Flat:-Defines one area upto 4
gigabytes for both code and data.It is unsegmented.The program uses 32-bit
adressing and runs under Windows in protected mode.
53.Difference between JMP and JNC?
A:-JMP is Unconditional Branch.
JNC is Conditional Branch.
54.List the String Manipulation Commands?
A:-REP=Repeat.
MOVS=Move Byte/Word
CMPS=Compare Byte/Word
SCAS=Scan Byte/Word
LODS=Load byte/Wd to AL/AX
STOS=Stor Byte/Wd from AL/A
55.What are the 4 Segments?
A:-Code Segment Register {CS}
Data Segment Register {DS}
Extra Segment Register {ES}
Stack Segment Register{SS}
56.What is the main use of ready pin?
A:-READY is used by the
microprocessor to check whether a peripheral is ready to accept or transfer
data.
A peripheral may be a LCD display
or analog to digital converter or any other.
These peripherals are connected to
microprocessor using the READY pin.
If READY is high then the
periphery is ready for data transfer. If not the microprocessor waits until
READY goes high.
57.Explain about Direction Flag?
A:-This is used by string
manipulation instructions.
If this flag bit is 0 , the
string is processed beginning from the lowest to the highest address,i.e.,.Autoincrement
mode.
Otherwise,the string is processed
from the highest towards the lowest address,i.e.,.Autodecrementing mode.
58.What are the basic units of a microprocessor ?
The basic units or blocks of a
microprocessor are ALU, an array of registers and control unit.
59.what is Software and Hardware?
The Software is a set of instructions
or commands needed for performing a specific task by a programmable device or a
computing machine.
The Hardware refers to the components
or devices used to form computing machine in which the software can be run and
tested. Without software the Hardware is an idle machine.
60.What is assembly language?
The language in which the mnemonics
(short -hand form of instructions) are used to write a program is called
assembly language. The manufacturers of microprocessor give the mnemonics.
61.What are machine language and assembly language programs?
The software developed using 1's
and 0's are called machine language,programs. The software developed using
mnemonics are called assembly language programs.
62. What is the drawback in machine language and assembly language, programs?
The machine language and assembly
language programs are machine dependent. The programs developed using these
languages for a particular machine cannot be directly run on another machine .
63. Define bit, byte and word.
A digit of the binary number or
code is called bit. Also, the bit is the fundamental storage unit of computer
memory.
The 8-bit (8-digit) binary number
or code is called byte and 16-bit binary number or code is called word. (Some
microprocessor manufactures refer the basic data size operated by the processor
as word).
64. What is a bus?
Bus is a group of conducting
lines that carries data, address and control signals.
65. Why data bus is bi-directional?
The microprocessor has to fetch
(read) the data from memory or input device for processing and after
processing, it has to store (write) the data to memory or output device. Hence
the data bus is bi-directional.
66. Why address bus is unidirectional?
The address is an identification
number used by the microprocessor to identify or access a memory location or I
/ O device. It is an output signal from the processor. Hence the address bus is
unidirectional.
67. What is the function of microprocessor in a system?
The microprocessor is the master
in the system, which controls all the activity of the system. It issues address
and control signals and fetches the instruction and data from memory. Then it
executes the instruction to take appropriate action.
68. What are the modes in which 8086 can operate?
The 8086 can operate in two modes
and they are minimum (or uniprocessor) mode and maximum ( or multiprocessor)
mode.
69. What is the data and address size in 8086?
The 8086 can operate on either
8-bit or 16-bit data. The 8086 uses 20 bit address to access memory and 16-bit
address to access 1/0 devices.
Explain the function of M/IO in 8086.
The signal M/IO is used to
differentiate memory address and 1/0 address When the processor is accessing
memory locations MI 10 is asserted high and when it is accessing 1/0 mapped
devices it is asserted low.
Write the flags of 8086.
The 8086 has nine flags and they
are
1. Carry Flag (CF) 6. Overflow
Flag (OF)
2. Parity Flag (PF) 7. Trace Flag
(TF)
3. Auxiliary carry Flag (AF) 8.
Interrupt Flag (IF)
4. Zero Flag (ZF) 9. Direction
Flag (DF)
5. Sign Flag (SF)
16. What are the interrupts of 8086?
The interrupts of 8085 are INTR
and NMI. The INTR is general
maskable interrupt and NMI is
non-maskable interrupt.
17. How clock signal is generated in 8086? What is the maximum internal
clock frequency of 8086?
The 8086 does not have on-chip
clock generation circuit. Hence the clock generator chip, 8284 is connected to
the CLK pin of8086. The clock signal supplied by 8284 is divided by three for
internal use. The maximum internal clock frequency of 8086 is 5MHz.
18. Write the special functions carried by the general purpose registers
of 8086.
The special functions carried by
the registers of 8086 are the following.
Register Special function
1. AX 16-bit Accumulator
2. AL 8-bit Accumulator
3. BX Base Register
4. CX Count Register
5. DX .Data Register
19. What is pipelined architecture?
In pipelined architecture the
processor will have number of functional units and the execution time of
functional units are overlapped. Each functional unit works independently most
of the time.
20. What are the functional units available in 8086 architecture?
The bus interface unit and
execution unit are the two functional units
available in 8086 architecture.\
21.
List the segment registers of 8086.
The segment registers of 8086 are
Code segment, Data segment, Stack segment and Extra segment registers.
22. Define machine cycle.
Machine cycle is defined as the
time required to complete one operation of accessing memory, I/O, or
acknowledging an external request. This cycle may consist of three to six
T-states.
23. Define T-State.
T-State is defined as one
subdivision of the operation performed in one clock period. These subdivisions
are internal states synchronized with the system clock, and each T-State is
precisely equal to one clock period.
24. List the components of microprocessor (single board microcomputer) based system
The microprocessor based system
consist of microprocessor as CPU, semiconductor memories like EPROM and RAM,
input device, output device and interfacing devices.
25. Why interfacing is needed for 1/0 devices?
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.
26. What is the difference between CPU bus and system bus?
The CPU bus has multiplexed lines
but the system bus has separate lines for each signal. (The multiplexed CPU
lines are demultiplexed by the CPU interface circuit to form system bus).
27..What does memory-mapping mean?
The memory mapping is the process
of interfacing memories to microprocessor and allocating addresses to each
memory locations.
28. What is interrupt 1/0?
If the 1/0 device initiate the
data transfer through interrupt then the 1/0 is called interrupt driven 1/0.
29. Why EPROM is mapped at the beginning of memory space in 8085 system?
In 8085 microprocessor, after a
reset, the program counter will have OOOOH address. If the monitor program is
stored from this address then after a reset, it will be executed automatically.
The monitor program is a permanent program and stored in EPROM memory. If EPROM
memory is mapped at the beginning of memory space, i.e., at OOOOH, then the
monitor program will be executed automatically after a reset.
31.What is DMA?
The direct data transfer between
I/O device and memory is called DMA.
32. What is the need for Port?
The I/O devices are generally
slow devices and their timing characteristics do not match with processor
timings. Hence the I/O devices are connected to system bus through the ports.
33.What is a port?
The port is a buffered I/O, which
is used to hold the data transmitted from the microprocessor to I/O device or
vice-versa.
34.Give some examples of port devices used in 8085 microprocessor
based system?
The various INTEL I/O port
devices used in 8085 microprocessor based system are 8212, 8155, 8156, 8255,
8355 and 8755.
35. Write a short note on INTEL 8255?
The INTEL 8255 is a I/O port
device consisting of 3 numbers of 8 –bit parallel I/O ports. The ports can be
programmed to function either as a input port or as a output port in different
operating modes. It requires 4 internal addresses and has one logic LOW chip
select pin.
36.What is the drawback in memory mapped I/0?
When I/O devices are memory
mapped, some of the addresses are allotted to I/O devices and so the full
address space cannot be used for addressing memory (i.e., physical memory
address space will be reduced). Hence memory mapping is useful only for small
systems, where the memory requirement is less.
37. How DMA is initiated?
When the I/O device needs a DMA
transfer, it will send a DMA request signal to 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 tri-stated pins to high impedance
state at the end of current instruction execution and send an acknowledge
signal to DMA controller. Now the DMA controller will perform DMA transfer.
38. What is processor cycle (Machine cycle)?
The processor cycle or machine
cycle is the basic operation performed by the processor. To execute an
instruction, the processor will run one or more machine cycles in a particular
order.
39. What is Instruction cycle?
The sequence of operations that a
processor has to carry out while executing the instruction is called
Instruction cycle. Each instruction cycle of a processor indium consists of a
number of machine cycles.
40. What is fetch and execute cycle?
In general, the instruction cycle
of an instruction can be divided into
fetch and execute cycles. The
fetch cycle is executed to fetch the opcode from memory. The execute cycle is
executed to decode the
instruction and to perform the
work instructed by the instruction.
41.What is Block and Demand transfer mode DMA?
In Block transfer mode, the DMA
controller will transfer a block of data and relieve the bus for processor.
After sometime another block of data is transferred by DMA and so on.
In Demand transfer mode the DMA
controller will complete the entire .data transfer at a stretch and then
relieve the bus to processor.
42. What is the need for timing diagram?
The timing diagram provides
information regarding the status of various signals, when a machine cycle is
executed. The knowledge of timing diagram is essential for system designer to
select matched peripheral devices like memories, latches, ports, etc., to form
a microprocessor system.
43. How many machine cycles constitute one instruction cycle in 8085?
Each instruction of the 8085
processor consists of one to five machine cycles.
44. Define opcode and operand.
Opcode (Operation code) is the
part of an instruction / directive that identifies a specific operation.
Operand is a part of an
instruction / directive that represents a value on which the instruction acts.
45. What is opcode fetch cycle?
The opcode fetch cycle is a
machine cycle executed to fetch the opcode of an instruction stored in memory.
Every instruction starts with opcode fetch machine cycle.
46. What operation is performed during first T -state of every machine
cycle in 8085 ?
In 8085, during the first T
-state of every machine cycle the low byte address is latched into an external
latch using ALE signal.
47. Why status signals are provided in microprocessor?
The status signals can be used by
the system designer to track the internal operations of the processor. Also, it
can be used for memory expansion (by providing separate memory banks for
program & data and selecting the bank using status signals).
48. How the 8085 processor differentiates a memory access (read/write) and
1/0 access (read/write)?
The memory access and 1/0 access
is differentiated using 10 I M signal.
The 8085 processor asserts 10 I M
low for memory read/write operation and 10 I M is asserted high for 1/0
read/write operation.
49. When the 8085 processor checks for an interrupt?
In the second T -state of the
last machine cycle of every instruction, the 8085 processor checks whether an
interrupt request is made or not.
50. What is interrupt acknowledge cycle?
The interrupt acknowledge cycle
is a machine cycle executed by 8085 processor to get the address of the
interrupt service routine in-order to service the interrupt device.
51. How the interrupts are affected by system reset?
Whenever the processor or system
is resetted , all the interrupts except TRAP are disabled. fu order to enable
the interrupts, El instruction has to be executed after a reset.
52. What is Software interrupts?
The Software interrupts are
program instructions. These instructions are inserted at desired locations in a
program. While running a program, if software interrupt instruction is
encountered then the processor executes an interrupt service routine.
53. What is Hardware interrupt?
If an interrupt is initiated in a
processor by an appropriate signal at the interrupt pin, then the interrupt is
called Hardware interrupt.
74. Where is the READY signal used?
READY is an input signal to the
processor, used by the memory or I/O devices to get extra time for data
transfer or to introduce wait states in the bus cycles.
75. What is HOLD and HLDA and how it is used?
Hold and hold acknowledge signals
are used for the Direct Memory Access (DMA) type of data transfer. The DMA
controller place a high on HOLD pin in order to take control of the system bus.
The HOLD request is acknowledged by the 8085 by driving all its tristated pins
to high impedance state and asserting HLDA signal high.
76.What is Polling?
Polling is a scheme or an
algorithm to identify the devices interrupting the processor. Polling is employed
when multiple devices interrupt the processor through one interrupt pin of the
processor.
77. What are the different types of Polling?
The polling can be classified
into software and hardware polling. In software polling the entire polling
process is govern by a prograrn.1n hardware polling, the hardware takes care of
checking the status of interrupting devices and allowing one by one to the
processor.
78.What is the need for interrupt controller?
The interrupt controller is
employed to expand the interrupt inputs. It can handle the interrupt request
from various devices and allow one by one to the processor.
79. List some of the features of INTEL 8259 (Programmable Interrupt Controller)
1. It manage eight interrupt request
2. The interrupt vector addresses are
programmable.
3. The priorities of interrupts are
programmable.
4. The interrupt can be masked or
unmasked individually.
80. What is a programmable peripheral device ?
If the functions performed by a
peripheral device can be altered or changed by a program instruction then the
peripheral device is called programmable device. Usually the programmable
devices will have control registers. The device can be programmed by sending
control word in the prescribed format to the control register.
81. What is synchronous data transfer scheme?
For synchronous data transfer
scheme, the processor does not check the readiness of the device after a
command have been issued for read/write operation. fu this scheme the processor
will request the device to get ready and then read/W1.ite to the device
immediately after the request. In some synchronous schemes a small delay is
allowed after the request.
82. What is asynchronous data transfer scheme?
In asynchronous data transfer
scheme, first the processor sends a request to the device for read/write
operation. Then the processor keeps on polling the status of the device. Once
the device is ready, the processor execute a data transfer instruction to
complete the process.
83. What are the operating modes of 8212?
The 8212 can be hardwired to work
either as a latch or tri-state buffer. If mode (MD) pin is tied HIGH then it
will work as a latch and so it can be used as output port. If mode (MD) pin is
tied LOW then it
work as tri- state buffer and so
it can be used as input port.
84. Explain the working of a handshake output port
In handshake output operation,
the processor will load a data to port.
When the port receives the data,
it will inform the output device to collect the data. Once the output device
accepts the data, the port will inform the processor that it is empty. Now the
processor can load another data to port and the above process is repeated.
85.What are the internal devices of 8255 ?
The internal devices of 8255 are
port-A, port-B and port-C. The ports can be programmed for either input or
output function in different operating modes.
86. What is baud rate?
The baud rate is the rate at
which the serial data are transmitted. Baud rate is defined as l /(The time for
a bit cell). In some systems one bit cell has one data bit, then the baud rate
and bits/sec are same.
87. What is USART?
The device which can be
programmed to perform Synchronous or Asynchronous serial communication is
called USART (Universal Synchronous Asynchronous Receiver Transmitter). The
INTEL 8251A is an example of USART.
88. What are the functions performed by INTEL 8251A?
The INTEL 825lA is used for
converting parallel data to serial or vice versa. The data transmission or
reception can be either asynchronously or synchronously. The 8251A can be used
to interface MODEM and establish serial communication through MODEM over
telephone lines.
89. What is an Interrupt?
Interrupt is a signal send by an
external device to the processor so as to request the processor to perform a
particular task or work.
90. What are the control words of 8251A and what are its functions ?
The control words of 8251A are
Mode word and Command word.
The mode word informs 8251 about
the baud rate, character length, parity and stop bits. The command word can be
send to enable the data transmission and reception.
91. What are the information that can be obtained from the status word
of 8251 ?
The status word can be read by
the CPU to check the readiness of the transmitter or receiver and to check the
character synchronization in synchronous reception. It also provides
information regarding various errors in the data received. The various error
conditions that can be checked from the status word are parity error, overrun
error and framing error.
92. Give some examples of input devices to microprocessor-based system.
The input devices used in the
microprocessor-based system are Keyboards, DIP switches, ADC, Floppy disc, etc.
93. What are the tasks involved in keyboard interface?
The task involved in keyboard
interfacing are sensing a key actuation, Debouncing the key and Generating key
codes (Decoding the key). These task are performed software if the keyboard is
interfaced through ports and they are performed by hardware if the keyboard is
interfaced through 8279.
94. How a keyboard matrix is formed in keyboard interface using 8279?
The return lines, RLo to RL7 of
8279 are used to form the columns of keyboard matrix. In decoded scan the scan
lines SLo to SL3 of 8279 are used to form the rows of keyboard matrix. In
encoded scan mode, the output lines of external decoder are used as rows of
keyboard matrix.
95. What is scanning in keyboard and what is scan time?
The process of sending a zero to
each row of a keyboard matrix and reading the columns for key actuation is called
scanning. The scan time is the time taken by the processor to scan all the rows
one by one starting from first row and coming back to the first row again.
96. What is scanning in display and what is the scan time?
In display devices, the process
of sending display codes to 7 -segment LEDs to display the LEDs one by one is
called scanning ( or multiplexed display). The scan time is the time taken to
display all the 7-segment LEDs one by one, starting from first LED and coming back
to the first LED again.
97. What are the internal devices of a typical DAC?
The internal devices of a DAC are
R/2R resistive network, an internal latch and current to voltage converting
amplifier.
98. What is settling or conversion time in DAC?
The time taken by the DAC to
convert a given digital data to corresponding analog signal is called
conversion time.
99. What are the different types of ADC?
The different types of ADC are
successive approximation ADC, counter type ADC flash type ADC, integrator
converters and voltage- to-frequency converters.
100. Define stack
Stack is a sequence of RAM memory
locations defined by the programmer.
101. What is program counter? How is it useful in program execution?
The program counter keeps track
of program execution. To execute a program the starting address of the program
is loaded in program counter. The PC sends out an address to fetch a byte of
instruction from memory and increments its content automatically.
102. How the microprocessor is synchronized with peripherals?
The timing and control unit synchronizes
all the microprocessor operations with clock and generates control signals necessary
for communication between the microprocessor and peripherals.
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