Microprocessor and Assembly Language

History of Microprocessor

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.

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.

 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

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.

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.

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.

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

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 Basic8085 Microprocessor

Flag Reg

Instruction Reg

Instruction decoder

Address Buffer A8-A15

B C

D E

H L

Stack Pointer

Program Counter

Incrementer/ DecrementerAddress latch

Data/address Buffer AD0-AD7

Temp. Reg

Accumulator

Arithmetic and Logic Unit

Timing and Control unit

RAM memory

8-bit_Internal_databus

Intel 8085 Microprocessor Architecture

8- bit External Data bus

ReadWriteClock

The 8085 has a set of registers for performing various operations. The various registers include:

Accumulator – 8 bit register which holds the latest result from ALU

B, C, D, E, H and L are general purpose registers

HL pair can be used for indirect addressing as well

Program counter – 16 bit register which holds the address of the next instruction to be executed

Instruction register – It holds the instruction that is currently being processed.

Stack pointer is used during subroutine calling and execution.

Address Latch – It increments/ decrements the address before sent to the address buffer

Various Flags

Sign Flag:If the result of the latest arithmetic operation is having MSB (most- significant 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.

Zero flag: If the result of the latest operation is zero, then zero flag will be set; otherwise it be reset.

Auxiliary Carry Flag: This flag is not accessible to programmer. This flag will be used by the system during BCD (binary-coded decimal) operations.

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.

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 MVI A, 21 ;Copies 21 into accumulator

202C MVI B, 2A ;Copies 2A into B register

202E ADD B ;Adds B reg content with Acc and stores the result in Acc.

202F STA 41 FF ; Stores the Acc (the sum) into the memory location

41 FF.

2032 HLT ; Stops the program

Memory storage of the Assembly language

Address Instruction/Data

202A MVI A, 202B 21202C MVI B, 202D 2A202E ADD B202F STA2030 FF2031 412032 HLT

Another example assembly language program

Address Instruction

2020 MVI B, 24 ;Copies 24 into accumulator

2022 INR B ;Increment B reg content by 1

2023 MOV A, B ;Copies B register into Acc.

2024 SUB B ;Subtracts B reg content from Acc and stores the

result in Acc.

2025 STA 5F FF ; Stores the Acc content into the memory location

5F FF.

2028 HLT ; Stops the program

Reference: http://www.brighthub.com/engineering/

electrical/articles/51225.aspx

http://www.cpu-world.com/Arch/8085.html

http://www.ehow.com/way_5230222_8085-microprocessor-tutorial.html

http://www.brighthub.com/engineering/electrical/articles/51225.aspx