Microprocessor and
Assembly Language
History of Microprocessor
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A microprocessor (sometimes abbreviated
µP) is a digital electronic component with
transistors on a single semiconductor
integrated circuit (IC).
A Central processing unit (CPU) in a
computer system or handheld device
consists of one or more microprocessors.
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A Microprocessor is essentially a set of
switches. Using photographic technology a
massive set of electronic switches is
superimposed onto a very small piece of
silicon.
Through the use of binary language, which
consists of only two states; one and zero (on
and off), these can be used to store
information and perform operations on it.
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A bit refers to one binary digit; a zero or one. In
computer memory and processing this refers to
the state of one switch. The transistors are
arranged into groups in order to represent
complex numbers and instructions
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The very first microprocessor is considered to
be the Intel 4004. It was released in 1971 and
was a 4 Bit processor.
Then the 8 bit 8008 microprocessor. It was
developed by Intel in 1972
The first multi-chip 16 bit processor was
released by National Semiconductor in 1973
Intel upgraded the 8008 into a 16 bit version
they called the 8086. It was the first of the
x86 family by which many modern PCs are
powered.
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32 bit designs didn't require much to improve
performance since it has double the size of
instructions as well as the amount of
addressable memory.
68000 by Motorola was one of the first
microprocessors developed to 32 bit
architectures. It was released in 1979 and
continued to be in use today.
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Most of today's computers are turning to 64
bit designs to handle dealing with very large
amounts of data. This is needed especially as
demand for 3D Graphics and fast video has
risen. E.g. AMD Athlon, Pentium i5/i7
processors.
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Microprocessors are classified into different types on the basis of the
bit of operation. Based on bit of operation at a time, the following are
the types of microprocessors:
==> 4 bit. e.g. Intel 4004
==> 8 bit. e.g. Intel 8085, 8088, Zilog Z80, Z180
==> 16 bit. e.g. Intel 8086, 80186, 80286, 80386,
==> 32 bit. e.g. Intel Pentium, Celeron, AMD Sempron
==> 64 bit. e.g. AMD Athlon.
Based on the instruction set microprocessors are classified into:
RISC — Reduced Instruction Set Computing. These types of
processors are commonly used in ovens, air conditioners, etc.
CISC — Complex Instruction Set Computing. The types of
processors are used in desktops, laptops and servers.
Microcomputer Block Diagram
Basic Block Diagram of
Microprocessor
Arithmetic
and Logic
Unit (ALU)
Register
Array
Timing and Control
unit
ALU – Performs all
arithmetic and logical
operations
Register array – Holds the
data temporarily for
processing
Control Unit – It supervises/
monitors all the operations
carried out in the computer
The 8085 Microprocessor
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The 8085 microprocessor was introduced by
Intel in the year 1976.
This microprocessor is an update of 8080
microprocessor. The 8080 processor was
updated with Enable/Disable instruction pins
and Interrupt pins to form the 8085
microprocessor.
It is an 8-bit microprocessor with a 40 pin
dual in line package
Pin Diagram of a Basic
8085 Microprocessor
Intel 8085 Microprocessor
Architecture
8-bit_Internal_databus
Accumulator
Temp.
Reg
Flag
Reg
Instruction
Reg
Arithmetic and
Logic Unit
Instruction
decoder
B
C
D
E
H
L
Stack Pointer
Program Counter
Incrementer/ Decrementer
Address latch
Address Buffer A8-A15
Data/address Buffer
AD0-AD7
Timing and Control unit
8- bit External
Data bus
Clock
Write
Read
RAM memory
The 8085 has a set of registers for performing various
operations. The various registers include:
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Accumulator – 8 bit register which holds the latest result from ALU
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B, C, D, E, H and L are general purpose registers
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HL pair can be used for indirect addressing as well
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Program counter – 16 bit register which holds the address of the next
instruction to be executed
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Instruction register – It holds the instruction that is currently being processed.
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Stack pointer is used during subroutine calling and execution.
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Address Latch – It increments/ decrements the address before sent to the
address buffer
Various Flags
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Sign Flag:If the result of the latest arithmetic operation is having MSB (mostsignificant byte) ‘1’ (meaning it is a negative number), then the sign flag is set.
Otherwise, it is reset to ‘0’ which means it is a positive number.
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Zero flag: If the result of the latest operation is zero, then zero flag will be set;
otherwise it be reset.
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Auxiliary Carry Flag: This flag is not accessible to programmer. This flag will
be used by the system during BCD (binary-coded decimal) operations.
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Parity Flag: If the result of the latest operation is having even number of ‘1’s,
then this flag will be set. Otherwise this will be reset to ‘0’. This is used for error
checking.
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Carry Flag: If the result of the latest operations exceeds 8-bits then this flag will
be set. Otherwise it be reset.
An example assembly
language program
Address Instruction
202A
202C
202E
MVI
MVI
ADD
A, 21
B, 2A
B
202F
STA
41 FF
2032
HLT
;Copies 21 into accumulator
;Copies 2A into B register
;Adds B reg content with Acc and
stores the result in Acc.
; Stores the Acc (the sum) into
the memory location 41 FF.
; Stops the program
Memory storage of the Assembly
language
Address
Instruction/Data
202A
202B
202C
202D
202E
202F
2030
2031
2032
MVI
21
MVI
2A
ADD
STA
FF
41
HLT
A,
B,
B
Another example assembly
language program
Address Instruction
2020
2022
2023
2024
MVI
INR
MOV
SUB
B, 24
B
A, B
B
2025
STA
5F FF
2028
HLT
;Copies 24 into accumulator
;Increment B reg content by 1
;Copies B register into Acc.
;Subtracts B reg content from
Acc and stores the result in Acc.
; Stores the Acc content into
the memory location 5F FF.
; Stops the program
Reference:

http://www.brighthub.com/engineering/electric
al/articles/51225.aspx
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http://www.cpu-world.com/Arch/8085.html
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http://www.ehow.com/way_5230222_8085microprocessor-tutorial.html

http://www.brighthub.com/engineering/electric
al/articles/51225.aspx