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Introduction to Microprocessors

Aim: to understand a generic microprocessor...

Nishant Kotian

on 24 October 2012

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Transcript of Introduction to Microprocessors

A microprocessor is a semi conductor, multipurpose, programmable logic device that reads binary instructions from a storage device called memory, accepts binary data as input and processes data according to the instructions and provides result as output. MICROPROCESSOR A microprocessor can also be viewed as an integrated circuit that contains processing capabilities of large computers. A microprocessor can also be considered as an electronic logic circuit that is capable of performing various computing tasks and making decisions to change the sequence of program execution. A microprocessor can also be considered as the center of any computing device that is expected to perform a logical task. HOW IS A μP MADE? μP’s are made mostly of an element called silicon. Silicon is rather common in earths crust and is a semiconductor. This means that depending on what materials you add to it, it can conduct when a voltage is applied to it. It is the 'switch that makes a CPU work. Modern μP's literally contain millions transistors. SILICON The first stage in making a CPU is to make the wafers that they are built on. This process begins with the melting of poly silicon, together with minute amounts of electrically active elements such as arsenic, boron, phosphorous or antimony in a quartz crucible.Then this entire mixture is then cooled and the wafer is cut out from it THE SILICON WAFER The wafers are then ground and polished both chemically and mechanically to produce a very flat, mirror like surface.
Wafers may then be heated to help remove any defects. (annealing)
The wafers are then inspected with a laser to find any surface defects. 1. Oxide A layer of oxide is implanted on the wafer. This is most often done by exposing the wafer to steam at very high temperatures
2. Photoresist A layer of organic photoresist is applied. This is like film in a camera
3. Masking A mask is applied and UV light is shown through the gaps. UV light is now used because of its shorter wavelength. A shorter wavelength means that it can pass through a smaller mask. The UV light hardens (fixes) the photoresist.
4. Cleaning The unhardened mask is removed with an organic solvent
5. Etching Hydroflouric (HF) acid is used to etch away the Silicon Oxide. Since HF is inorganic it does not attack the photoresist.
6. Cleaning The remaining photoresist is washed away. The wafer is now ready for doping with another type of silicon. Or for adding contacts. (A) A p-type wafer (silicon doped with Boron) has a epilayer of n-type (silicon doped with Phosphorous or Arsenic)
(B) A mask is used to implant Silicon Dioxide, for the insulator
(C) Acceptor atoms (Boron) are diffused into the window in the Silicon Dioxide
(D) Using another mask additional Silicon Dioxide is grown. and donor atoms (elements like Arsenic with excess electrons) are implanted.
(E) Another mask is used to grow additional Silicon Dioxide. ANother mask is then used to implant evaporated Aluminum or Copper for the contacts. This is a Bipolar Junction Transistor (BJT). We know that our computers use microprocessors to do their work. Smaller and thinner than a dime, these tiny silicon chips contain millions of transistors that work together to help you do everything from write a college report to search the Web for everything under the sky.
We know how they are made, but how do they do all the things they do?
Let's shrink ourselves down and explore the world of microprocessors. ALU This unit performs arithmetic and logic operations.
This unit also preforms rotate operation.
The operations in this unit affect the status register.
The results from the ALU are placed in the accumulator. It is a 8-bit register used to store 8-bit data.
In arithmetic and logic operation, result is store in accumulator. Accumulator It is also known as flags, which consists of flip-flops that are set or reset according to data conditions in the accumulator. Status register It is a 16-bit register containing the address of the next executable instruction.
It can be incremented or reset by the control selection. Program Counter It is a 16-bit register consisting of address of the memory location called stack.
Stack is R/W memory used for temporary storage. Stack Pointer H L It is a pair of 8-bit registers that can be used separately or as a combined pair. They are labeled as H & L.
Data is stored in these registers. When used in pair, 16 bit address can also be stored. Data/Address register This interprets the content of the instruction register and determines exact steps to be followed in executing the entire instruction.
It directs the control section accordingly. Instruction
Decoder This section receives the signals form the instruction decoder to determine the nature of the instruction to be executed.
Timing and control signals are sent to all parts of the microprocessor. Timing & Control Unit It is a group of 16 lines generally identified as A0 to A15.
It is a uni directional bus i.e. data flows in both directions between MPU and peripheral. Address Bus Data bus is a group of 8-bits used to transfer data.
It is a bidirectional bus i.e. data flows in both directions between MPU memory and peripheral. Data Bus Latch is flip-flop used to store one bit of information.
Information is stored into the latch by enabling the buffer. Bus buffer
Latches Latch is flip-flop used to store one bit of information.
Information is stored into the latch by enabling the buffer. Bus buffer
Latches Complementor
Shifter Addcr Temporary
register Instruction
Register Internal bus Internal bus ALU Registers Control Unit The Arithmetic and Logic Unit(ALU) is responsible for all arithmetical and logical operations carried out. Registers are primarily used to store data temporarily during the execution of the program. Control Unit provides timing and control signals to the whole system CLK clock x1 x2 Crystal +5V GND Power Supply Interrupt request Interrupt
control INTR Reset Write Read This is an 8-bit register
The first byte of an instruction is stored in this register IN DAILY LIFE FROM AIR-CRAFTS
HAS A BRAIN CALLED 8085 1977 What makes 8085
legendary Intel’s 8085 is an 8-bit microprocessor, 8-bit data bus width indicates that 1 byte of data can be passed on this bus.
8085 chip is available in 40 pin plastic ceramic DIP package.
It has 16 bit address bus that means it can address a physical memory of 64 kilo bytes. To communicate with external devices 8085 uses the hardware interrupt method.
To select external memory or I/O devices ,80885 uses I/O mapped I/O system.
The microprocessor requires +5V single power supply and can operate with 3MHz single phase clock. Address is divided into groups. The least significant 8 bits of address bus are transferred on the same eight lines of the data bus. Such a bus is called a multiplexed bus. Most significant bits of the address are transmitted on the address bus. A15 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Enable D7 D6 D5 D4 D3 D2 D1 D0 8
5 latch 7
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