8085 microprocessor ramesh gaonkar, Essays (university) of Electrical Engineering

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MICROPROCESSOR 8085

• Reference Book:
  • Ramesh S. Goankar, “Microprocessor Architecture, Programming and Applications with 8085”, 5 th^ Edition, Prentice Hall
• Week 1 – Basic Concept and Ideas about Microprocessor.
• Week 2 - Architecture of 8085
• Week 3 - Addressing Modes and Instruction set of 8085
• Week 4 – Interrupts of 8085
• Week 5 onwards – Peripherals.

What is a Microprocessor?

• The word comes from the combination micro and

processor.

• Processor means a device that processes whatever. In this context processor means a device that processes numbers, specifically binary numbers, 0’s and 1’s. - To process means to manipulate. It is a general term that describes all manipulation. Again in this content, it means to perform certain operations on the numbers that depend on the microprocessor’s design.

What about micro?

• Micro is a new addition.
  • In the late 1960’s, processors were built using discrete elements. - These devices performed the required operation, but were too large and too slow.
  • In the early 1970’s the microchip was invented. All of the components that made up the processor were now placed on a single piece of silicon. The size became several thousand times smaller and the speed became several hundred times faster. The “Micro”Processor was born.

Definition of the Microprocessor

The microprocessor is a programmable device

that takes in numbers, performs on them

arithmetic or logical operations according to

the program stored in memory and then

produces other numbers as a result.

Definition (Contd.)

• Lets expand each of the underlined words:
  • Programmable device: The microprocessor can perform different sets of operations on the data it receives depending on the sequence of instructions supplied in the given program. By changing the program, the microprocessor manipulates the data in different ways.
  • Instructions: Each microprocessor is designed to execute a specific group of operations. This group of operations is called an instruction set. This instruction set defines what the microprocessor can and cannot do.

Definition (Contd.)

• Numbers: The microprocessor has a very narrow view on life. It only understands binary numbers.

A binary digit is called a bit (which comes from b inary dig it ).

The microprocessor recognizes and processes a group of bits together. This group of bits is called a “word”.

The number of bits in a Microprocessor’s word, is a measure of its “abilities”.

Definition (Contd.)

• Words, Bytes, etc.
  • The earliest microprocessor (the Intel 8088 and Motorola’s
    6800. recognized 8-bit words.

    - They processed information 8-bits at a time. That’s why they are called “8-bit processors”. They can handle large numbers, but in order to process these numbers, they broke them into 8-bit pieces and processed each group of 8-bits separately. 

  • Later microprocessors (8086 and 68000) were designed with 16-bit words. - A group of 8-bits were referred to as a “half-word” or “byte”. - A group of 4 bits is called a “nibble”. - Also, 32 bit groups were given the name “long word”.
  • Today, all processors manipulate at least 32 bits at a time and there exists microprocessors that can process 64, 80, 128 bits

Definition (Contd.)

• Stored in memory :
  • First, what is memory?
    • Memory is the location where information is kept while not in current use.
    • Memory is a collection of storage devices. Usually, each storage device holds one bit. Also, in most kinds of memory, these storage devices are grouped into groups of 8. These 8 storage locations can only be accessed together. So, one can only read or write in terms of bytes to and form memory.
    • Memory is usually measured by the number of bytes it can hold. It is measured in Kilos, Megas and lately Gigas. A Kilo in computer language is 2 10 =1024. So, a KB (KiloByte) is 1024 bytes. Mega is 1024 Kilos and Giga is 1024 Mega.

Definition (Contd.)

• Stored in memory:
  • When a program is entered into a computer, it is stored in memory. Then as the microprocessor starts to execute the instructions, it brings the instructions from memory one at a time.
  • Memory is also used to hold the data.
    • The microprocessor reads (brings in) the data from memory when it needs it and writes (stores) the results into memory when it is done.

Memory

Input Output

A Microprocessor-based system

From the above description, we can draw the

following block diagram to represent a

microprocessor-based system:

Inside The Microprocessor

• Internally, the microprocessor is made up of

3 main units.

• The Arithmetic/Logic Unit (ALU)
• The Control Unit.
• An array of registers for holding data while it is

being manipulated.

Memory

• Memory stores information such as instructions

and data in binary format (0 and 1). It provides

this information to the microprocessor whenever

it is needed.

• Usually, there is a memory “sub-system” in a

microprocessor-based system. This sub-system

includes:

• The registers inside the microprocessor
• Read Only Memory (ROM)
  • used to store information that does not change.
• Random Access Memory (RAM) (also known as Read/Write Memory). - used to store information supplied by the user. Such as programs and data.

Memory Map and Addresses

• The memory map is a picture representation

of the address range and shows where the

different memory chips are located within

the address range.

0000

FFFF

Address Range

RAM 1 RAM 2 RAM 3

RAM 4

EPROM

0000 3FFF 4400 5FFF 6000

8FFF 9000 A3FF A

F7FF

Address Range of EPROM Chip

Address Range of 1st^ RAM Chip Address Range of 2nd^ RAM Chip Address Range of 3rd^ RAM Chip

Address Range of 4th^ RAM Chip