Computer Organization - 1

• INPUT PROCESS OUTPUT

• List different input devices• Compare the use of voice recognition as

opposed to the entry of data via the keyboard

Components of a system

What does the CPU do?• Carries out instructions and tells the

computer what to do – done through Control Unit which sends commands to other components of the system.

• Performs arithmetic calculations and data manipulation (eg. comparisons, sorting, combining, etc.) This part of the CPU known as the Arithmetic Logic Unit.

• Holds data and instructions which are in current use. These are kept in the Main Store or Memory.

Control Unit (CU)That part of the computer which accesses instructions in sequence, interprets them and then directs their Implementation – literally in

control.

What it does:1. Directs the entire computer system to carry out stored program

instructions2. Communicates with both the arithmetic logic unit and main

memory3. Uses the instruction contained in the Instruction Register to

decide which circuits need to be activated4. Co-ordinates the activities of the other two units as well as all

peripheral and auxiliary storage devices linked to the computer.

Arithmetic Logic Unit (ALU)The part of the CPU where arithmetic and logic operations

are performed. Sometimes called the arithmetic unitWhat it does:1. Executes arithmetic operations like addition,

subtraction, multiplication and division2. Executes logical operations which compare numbers,

letters and special characters (=, <, >)3. Performs logic functions such as AND, OR and NOT

Made up of:4. Accumulator is used to accumulate results. It is the

place where the answers from many operations are stored temporarily before being put out to the computer's memory

5. General-purpose registers hold data on which operations are to be performed by the arithmetic logic unit.

Primary Memory

• part of the computer that holds data and instructions for processing

• Although it is closely associated with the CPU, in actual fact it is separate from it

• When we load software from a hard disk or CD-ROM, it is stored in the Primary Memory

• There are two types of computer memory: • RAM and ROM

RAM / ROMRandom Access Memory (RAM)

• The main store and is the place where the programs get stored

• When the CPU runs a program, it fetches the program instructions from the RAM and carries them out.

• CPU stores calculation results here

• Can have instructions READ or WRITTEN

• When computer is switched off RAM is lost

Read Only Memory (ROM)• CPU can only read files stored

here• comes with instructions

permanently stored inside and these instructions cannot be over-written.

• used for storing special sets of boot up instructions.

• When computer is turned off ROM is still alive.

Memory Access-Address Bus

• Series of wires connecting CPU and memory unit and is used to identify locations (addresses) within memory

• The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed.

• Modern computers have as many as 36 address lines, which enables them theoretically to access 64 GB (gigabytes) of main memory

Microprocessors

• Devices similar to CPU with a single program stored in non-volatile memory

• Used to control various devices– Control fuel injection system s in cars– Washing machine controls– Photocopier controls– Security systems– Automatic cameras (exposure, image conversion)

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Microprocessor Architecture• The microprocessor can be programmed to

perform functions on given data by writing specific instructions into its memory.– The microprocessor reads one instruction at a time,

matches it with its instruction set, and performs the data manipulation specified.

– The result is either stored back into memory or displayed on an output device.

• Single instruction fetch – decode – execute was Von Neumann design. Now you have multiple pipeline architecture

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The 8085 Architecture

• The 8085 uses three separate busses to perform its operations– The address bus.– The data bus.– The control bus.

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The Address Bus

– 16 bits wide (A0 A1…A15)• Therefore, the 8085 can access locations with numbers from 0 to

65,536. Or, the 8085 can access a total of 64K addresses.

– “Unidirectional”.• Information flows out of the microprocessor and into the

memory or peripherals.

– When the 8085 wants to access a peripheral or a memory location, it places the 16-bit address on the address bus and then sends the appropriate control signals.

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The Data Bus

– 8 bits wide (D0 D1…D7)– “Bi-directional”.

• Information flows both ways between the microprocessor and memory or I/O.

– The 8085 uses the data bus to transfer the binary information.

– Since the data bus has 8-bits only, then the 8085 can manipulate data 8 bits at-a-time only.

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The Control Bus

– There is no real control bus. Instead, the control bus is made up of a number of single bit control signals.

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Microprocessor Initiated Operations

• These are operations that the microprocessor itself starts.

• These are usually one of 4 operations:– Memory Read– Memory Write– I/O Read (Get data from an input device)– I/O write (Send data to an output device)

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The Read Operation

– To read the contents of a memory location, the following steps take place:• The microprocessor places the 16-bit address of the

memory location on the address bus. • The microprocessor activates a control signal called

“memory read” which enables the memory chip.• The memory decodes the address and identifies the

right location. • The memory places the contents on the data bus. • The microprocessor reads the value of the data bus

after a certain amount of time.

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Dimensions of Memory• Memory is usually measured by two numbers: its length and

its width (Length X Width).• The length is the total number of locations.• The width is the number of bits in each location.

– The length (total number of locations) is a function of the number of address lines.

# of memory locations = 2( # of address lines)

• So, a memory chip with 10 address lines would have 210 = 1024 locations (1K)

• Looking at it from the other side, a memory chip with 4K locations would need

Log2 4096=12 address lines

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The 8085 and Memory

• The 8085 has 16 address lines. That means it can address 216 = 64K memory locations. – Then it will need 1 memory chip with 64 k locations,

or 2 chips with 32 K in each, or 4 with 16 K each or 16 of the 4 K chips, etc.

• how would we use these address lines to control the multiple chips?

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Chip Select

• Usually, each memory chip has a CS (Chip Select) input. The chip will only work if an active signal is applied on that input.

• To allow the use of multiple chips in the make up of memory, we need to use a number of the address lines for the purpose of “chip selection”.– These address lines are decoded to generate the 2n

necessary CS inputs for the memory chips to be used.

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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

Addr

ess

Rang

e

RAM 1

RAM 2

RAM 3

RAM 4

EPROM0000

3FFF4400

5FFF6000

8FFF9000

A3FFA400

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

Project work - 10pts• Find information on the first programmer.

OR• Find information on ENIAC

OR• RISC architecture

OR• Cache memory Vs. RAM

OR• Find information on Machine Instruction CyclePrint a poster to display in class.