Introduction to Microprocessor
and Computer
History of computer
Computing device
Year of invention
Description
Abacus
2700-2300 BC
It is a calculating tool. It uses beans or stones moved in
grooves in sand or on tablets of wood, stone, or metal.
Pascal's calculator
1642
It is a mechanical calculator invented by Blaise Pascal. It uses
gears which are numbered from 0-9.
Difference engine
1822
It is an automatic mechanical calculator designed to
tabulate polynomial functions.
Electronic Numerical
Integrator and
Computer(ENIAC)
1946
it was amongst the earliest electronic generalpurpose computers made.
4004 Microprocessor
1971
It was the first commercially available microprocessor by Intel.
Block diagram of computer
Microprocessor
ALU
Control unit
Input device
Bus
Bus
Register Array
B
u
s
Memory
Output device
Introduction to computer
• Input device : is a device that is used to input data and control signal
into a computer. E.g. keyboard, mouse , scanner …
• Output device : is a device that is used to get( receive ) output from a
computer. E.g. monitor, speaker,
• Memory : is a storage device that is used to hold data and instruction
temporarily or permanently in a computer. E.g. ROM, RAM, Hard Disk
• Microprocessor: is a device that accept an input data and process it
using defined instruction to give an output.
Introduction to microprocessor
• Microprocessor is an integrated circuit that contains all the functions
of a computers central processing unit (CPU).
• Microprocessors can be found inside computer, mobile, calculator,
television, embedded systems (microcontroller) …
• Any electronic circuit that can be programmable to do some
operations can be called microprocessor.
• A microprocessor include a ALU, registers, control unit and bus.
Introduction to microprocessor
• ALU : is a circuit in microprocessor that perform arithmetic and
bitwise logic operations.
• Arithmetic operations are addition, subtraction, multiplication,
division …
• Logic operations are NEG, OR, AND ,XOR …
• Control unit: is a component in microprocessor that control the flow
of instruction and data between ALU, input/output devices and
memory.
• Registers: are stack of memory that can store 8-bit, 16- bit, 32-bit or
64-bit data at a time.
Introduction to microprocessor
• Bus : is a collection of wires that are used to transfer data in a form of
signals (bits).
• There are 3 types of buses those are data bus, address bus and
control bus.
• Data bus are buses that are used to transfer data between
components of computer or microprocessor.
• The width of data bus tell how much bit the microprocessor can read
or write into memory and input/output device at a time.
• Data bus is bidirectional. It means bits can be transferred both
directions.
Introduction to microprocessor
• Address bus are buses that are used to carry the address of memory
or input/output device from which data will be read or write to.
• The width of address bus can tell as how much memory size we can
address. It n-bit address bus can support 2n memory.
• E.g. 8-bit address bus can support 28=256 byte.
• Address bus is unidirectional bus.
• Control bus are buses that tell what kind of operation we be done
with the memory or input/output device.
• Like read memory, write memory, read I/O and write I/O
Introduction to microprocessor
• Control bus is unidirectional.
Microprocessor
Memory
Input
Control bus
Data bus
Address bus
output
Introduction to microprocessor
• Microprocessor has 3 basic operations. Those are fetching, decoding
and executing instructions.
• Fetching is the processes of getting instructions to be processed from
memory or input/output.
• Decoding is understanding what kind of operation the instruction will
perform.
• Executing is the running the operation ( executing the instruction).
Introduction to microprocessor
• Every microprocessor has a list of instruction that can process.
• This list of instruction are recognized by decoder and called
instruction set.
• Depending on the type of instruction set microprocessor can be of 2
type CISC and RISC.
• CISC (complex instruction set computer) is a microprocessor designed
to have a single instruction perform multiple low level operation like
load from memory, arithmetic operation and store to memory.
• RISC (reduced instruction set computer) is a microprocessor in which
all its instructions are designed to processes only one operation.
Introduction to microprocessor
• Difference between CISC and RISC
CISC
RISC
CSIC processor has complex instructions
that take up multiple clocks for
execution.
RISC processors have simple instructions
taking about one clock cycle.
It has a micro-programming unit.
It has a hard-wired unit of programming.
Decoding of instructions is complex.
Decoding of instructions is simple.
Execution time is very high.
Execution time is very less.
It has a memory unit to implement
complex instructions.
It has no memory unit and uses a
separate hardware to implement
instructions.
It is an easy complier design.
It is a complex complier design.
Introduction to microprocessor
• Special processor are processors which are designed for some special
purposes. They use as supporting processor for microprocessors.
• A coprocessor is a specially designed microprocessor, which can
handle its particular function many times faster than the ordinary
microprocessor.
• I/O processor is a specially designed microprocessor having a local
memory of its own, which is used to control I/O devices with
minimum CPU involvement.
• DSP (Digital Signal Processor) is specially designed to process the
analog signals into a digital form.
Characteristics of microprocessor
• Instruction Set − It is the set of instructions that the microprocessor can
understand.
• Bandwidth − It is the number of bits processed in a single instruction.
• Clock Speed − It determines the number of operations per second the
processor can perform. It is measured in hertz.
• Word Length − It depends upon the width of internal data bus, registers, ALU,
etc. An 8-bit microprocessor can process 8-bit data at a time.
• Data Types − The microprocessor has multiple data type formats like binary,
BCD, ASCII, signed and unsigned numbers.
Features of a Microprocessor
• Features of a Microprocessor
•
•
•
•
Cost-effective :microprocessor chips are available at low prices.
Size : microprocessor is of small size chip.
Low Power Consumption
Versatility : it can be used in a number of applications by configuring the
software program.
• Reliability − The failure rate of an IC in microprocessors is very low.
Different types of Intel microprocessor
Microprocessor
Data bus width
Memory size
4004
4-bit
4KB
8008
8-bit
16KB
8086
16-bit
1 MB
80386DX
32-bit
4 GB
Pentium
64-bit
4G + 16K cache
Core2(dual core)
64
1T + 32K L1 cache + a shared
2 or 4 M L2 cache
Itanium (Dual Core)
128
1T + 2.5 M L1 and L2 cache
+ 24 M L3 cache
8086 microprocessor
• 8086 microprocessor is the first 16-bit microprocessor build by intel in
the year 1976.
• It has 20-bit address bus and 16-bit data bus so it can support 1Mega
byte memory.
Features of 8086 microprocessor
• Features of 8086 microprocessor
• It has 6 byte instruction queue
• It is 16-bit microprocessor having 16-bit ALU, 16-bit registers and 16-bit
internal bus.
• It was available in 3 modes
• 8086 → 5MHz
• 8086-2 → 8MHz
• (c)8086-1 → 10 MHz
• It use two stage pipeline one for fetching instruction the other for executing
instruction.
8085 vs 8086 microprocessor
Characteristic
Intel 8085
Intel 8086
size
8-bit
16-bit
Address bus
16-bit
20-bit
Memory
64 kilobyte
1 megabyte
Instruction queue
Doesn’t have
Have an instruction queue
Pipelining
Doesn’t support
support
Input/output
28=256 I/O’s
216=65,536 I/O's
8088 vs 8086 microprocessor
• 8086 and 8088 have similar architecture except for those points.
• 8086 vs 8088
• 8088 has 8-bit external data bus where as 8086 has 16-bit external data bus.
• 8088 has a queue size 4 byte where as 8086 has 6 byte size queue.
• 8088 is 30% less in speed than 8086.
• 8088 microprocessor was built in order to support peripheral devices
which are intractable with 8-bit bus.
Architecture of 8086 microprocessor
EU and BIU
• 8086 microprocessor has to parts. These are Bus Interface Unit(BIU)
And Execution unit(EU).
• Bus interface unit is used to fetch instruction and data to be used by
execution unit.
• Execution unit is used to decode and execute an instruction given by
Bus interface unit.
EU and BIU
• Functionality of Bus interface unit
•
•
•
•
Fetch instruction and data from memory
Write data to memory
Write data to port
Read data from port
• Functionality of Execution unit
• Tell BIU where to fetch the instruction or data
• Decode an instruction
• Execute an instruction
Pipelining
• Non-pipelined architecture
Time
Fetch
Decode
Execute
Fetch
Decode
Execute
• Pipelined architecture
• BIU
• EU
Fetch
Fetch
Fetch
Wait
Decode
Execute
Fetch
Decode
Fetch
Execute
Decode
Fetch
Wait
Fetch
decode
Pipelining
• 8086 microprocessor BIU will be used to fetch instruction where as
EU will be used to decode and execute that instruction.
• When instruction is being executed another instruction will be
fetched at the same time.
• In execution unit wait can happen if
• The requested data not in the queue
• Jump instruction has happened
Memory segmentation
• 8086 has address bus 20-bit so it allow it to address 1 megabyte
memory from 00000H to FFFFFH.
• Because 8086 is 16-bit processor its internal bus width is 16-bit
allowing it only to access a memory size between 0000H-FFFFH or 64
kilobyte memory.
• Because of this reason the 1 megabyte memory is divided into
segments of 64 kilobyte memory.
• In 8086 microprocessor there are 4 segments data segment, code
segment, extra segment and stack segment.
Memory segmentation
• The physical address of a memory is found by adding the segment
address and an offset address.
• E.g. If the segment address=12340 and off set address is =12FFH
• The physical address of the memory will be
• Physical address= segment address+ offset address
• Physical address= 12340H+12FFH
• Physical address=1263FH
• The physical address is expressed in segment address : offset address.
Memory segmentation
8086 segments
• Code segment are used to store programs that are run by 8086.
• Data segment are segments where data is stored.
• Extra segment is used to store data and mostly it is used for string
operation.
• Stack segment is used to store temporary data. It is used as stack
memory when we use the instruction pop and push. It is also used to
hold address of next instruction when there is a call instruction.
• The segment address of segments are stored in the segment registers.
Segment registers
• Segment registers are registers which are used to hold the address of
the segment memory.
• Those registers are CS, DS, ES and SS.
• CS register is used to hold the segment address of code segment.
• DS register is used to hold the segment address of Data segment.
• ES register is used to hold the segment address of Extra segment.
• SS register is used to hold the segment address of Stack segment.
Segment registers
Segment
Offset
Special purpose
CS
IP
Instruction address
DS
BX,SI,DI, 8-bit or 16 –bit
number
Data address
ES
DI
String destination address
SS
SP or BP
Stack address
Segment registers
• E.g. data in CS register is 5673H and data in IP register is 0342H the
next instruction to be fetched will be.
• Physical address will segment address + offset address. So
• The segment address for CS register data multiplied by 10H
• And the offset address will be the IP register data.
• Next instruction address= (5673HX10H)+0342H
• Next instruction address= 56730H+0342H
• Next instruction address=56A72H
General purpose registers
• General purpose registers are registers that are used for storing
temporary data.
Register name
Bit size
Special operation
AX(accumulator)
(AH,AL)
AX=16
AH,AL=8
For multiplication , division : in mul and div instructions one
operand must be accumulator
BX (base)
(BH,BL)
BX=16
BH,BL=8
Store address information : hold the offset address of memory
address.
CX (counter)
(CH,CL)
CX=16
CH,CL=8
Use as counter in loop, shift and rotate instructions.
DX (data )
(DH,DL)
DX=16
DH,DL=8
Used on word size multiplication and division and to hold the
port number of input/output
8086 registers
Register name
operation
SP (stack pointer)
Points the address of stack memory. It is used as offset address
for stack segment
BP (base pointer)
It points memory location for data transfer.
SI (source index)
The source index register often addresses source string data for
string instructions.
DI (destination index)
often addresses string destination data for the string
instructions.
IP (instruction pointer)
Points the address of the next instruction. It address the code
segment.
Flag register
• Flag register indicate the condition of the microprocessor and control
its operation.
Flag register
• Status flags tell as the status of the microprocessor.
• Carry holds the carry after addition or the borrow after subtraction. The carry
flag also indicates error conditions, as dictated by some programs and
procedures. If carry happen it is set.
• Parity is the count of ones in a number expressed as even or odd. If the parity
count is even it is set.
• Auxiliary flag: It is set if a carry is generated out of the lower nibble to higher
nibble.
• Zero flag: it is set if the result is zero.
• Sign flag: in signed numbers It is set if the MSB of the result is 1. For signed
operations such a number is treated as negative.
• Overflow flag : It will be set if the result of a signed operation is too large to fit
in the number of bits available to represent it.
Flag register
• Control flags are flags that control the operation of the execution.
• Trap flag: It is used to set the trace mode i.e. start single stepping mode. Here
the microprocessor is interrupted after every instruction so that the program
can be debugged.
• Interrupt flag: It is used to mask (disable) or unmask (enable) the INTR
interrupt.
• Direction flag: it is used for string operation memory addressing. if it is set
memory is accessed from higher to lower.