1. Microprocessor and Assembly Language

2. 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.

3. A Microprocessor is essentially a set of switches
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.

4. A bit refers to one binary digit; a zero or one
 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

5. The very first microprocessor is considered to be the Intel 4004
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.

6. 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.

7. 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.

8. 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.

9. Microcomputer Block Diagram

10. 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

11. 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

12. Pin Diagram of a Basic
8085 Microprocessor

13. Intel 8085 Microprocessor Architecture
8-bit_Internal_databus
Accumulator
Temp. Reg
Flag Reg
Instruction Reg
B C
D E
Arithmetic and Logic Unit
H L
Instruction decoder
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
RAM memory
Clock
Write
Read

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

15. 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.

16. 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

17. Memory storage of the Assembly language
Address Instruction/Data
202A MVI A,
202B 21
202C MVI B,
202D 2A
202E ADD B
202F STA
2030 FF 41
2032 HLT

18. 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

19. Reference: