Central Processing Unit and Memory Location

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MICROPROCESSOR 8085
• Reference Book: – Ramesh S. Goankar, “Microprocessor Architecture, Programming and Applications with 8085”, 5th 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.

Basic Concepts of Microprocessors
• Differences between:
– Microcomputer – a computer with a microprocessor as its CPU. Includes memory, I/O etc. – Microprocessor – silicon chip which includes ALU, register circuits & control circuits – Microcontroller – silicon chip which includes microprocessor, memory & I/O in a single package.

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.

Was there ever a “mini”processor?
• No.
– It went directly from discrete elements to a single chip. However, comparing today’s microprocessors to the ones built in the early 1970’s you find an extreme increase in the amount of integration.

• So, What is a microprocessor?

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.)
– Takes in: The data that the microprocessor manipulates must come from somewhere. • It comes from what is called “input devices”. • These are devices that bring data into the system from the outside world. • These represent devices such as a keyboard, a mouse, switches, and the like.

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 binary digit). 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...
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