AR Lecture2

8/11/2019 AR Lecture2

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ECE 2211

Microprocessor and Interfacing

Br. Athaur Rahman Bin Najeeb

Room 2.105

Email: [email protected]: http://eng.iiu.edu.my/~athaur

Consultation : Tuesday 10.00 am ( appointment)

The Basics

BASICS:

Terms and terminology

Used in this course


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Bus a bus is a set of wires; conductors. Basically its subsystem that transfers data

between MP and other component [ memory, peripheral devices ]

Collection of electronic signal dedicated to particular task.

1 bus = 1 wire ; The size of the bus is the number of wires in the bus

parallel data communication path over which information is transferred a byteor word at a time

8 bit bus has 8 parallel bus / 16bit bus has 16 parallel wires , 32, 64,

The busses contains logic that MP controls: data transfer, instructions,commands

Signal flow between of a bus can be UNIDIRECTIONAL or BIDIRECTIONAL

Bus - Types All computers use three types of basic buses. The name of the bus is generally

determined by the type of signal it is carrying or the method of operation

Types:

ADDRESS BUS

DATA BUS

CONTROL BUS


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Data Bus ( Memory Bus)

handles the transfer of all data and instructions

Its Bi-directional but data can only transmit in one direction at a time

Typical operations are

- transfer instructions from memory to the MP for execution.- It carries data (operands) to and from the MP

- transfer data between memory and I/O devices during I/OOperation

Reading or writing - transmitting or Receiving( from MP )

Faster processing means more data bus, but more expensive, designconsideration, heat dissipation, processor speed

Address Bus An address is defined as labels ( set of characters in hexa) to designate a location of

a memory or I/O

Before an instruction ( Mem or I/O operations ) to take place, an address is totransmitted over the address bus

MP selects particular address for reading/writing ( identify the memory or I/O addressthe MP would like to communicate with )

Unidirectional Bus , the MP transmit the add

A MP with x-bit address bus corresponds to addresses of memory location

Ex : 8088 / 8086 has 20 bit address bus .. What is the maximum memory ?

Pentium 4 has 4G of Main memory .. How many address line it has ?

.

x2


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Control Bus How do we know the address on Address bus is memory address or I/O address ? We can

have Memory Read , Memory Write I/O read , I/O write

Its a unidirectional bus Controlled over Control signals provided by the MP

MULTIPLEXED BUS

On both the 8086 and 8088processors the address and databuses are multiplexed.same pins are used to carry bothaddress and data information atdifferent times during the read orwrite cycle. At the start of the cycle theaddress/data bus carries theaddress signals, while at the endof the cycle the pins are used for

the data bus.

How MP difference it ?

Bus Standard


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Numbering System

Decimal ( base10) - 8(10),

Numbers- 0,1,2,3,4,5,6,7,8,9

Binary (base2) 1100(2)

Numbers- 0 and 1

Hexadecimal (base16) A8(16) /A8(H)

Numbers- 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F

Binary Numbers Bit is a binary digit that can have the value 0 or 1. Base 2 Binary numbers are used to store both instruction and data Address, Data , Signal are transmitted in binary ALU performs calculation in binary Instructions are converted to MACHINE CODES ,

binary numbers EX : MOV AX, BX

.

MSB

LSB

1111011

126 + 125 + 124 + 123 + 022 + 121 + 120

= 164 + 132 + 116 + 18 + 04 + 12 + 11

= 123


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Binary Numbers Terms

A byte is defines as 8 bits

A nibble is half a byte A word is 2 bytes

A doubleword is 2 words

A doubleword is 4 bytes

A quadword is 2 doublewords

A kilobyte is bytes, that is 1,024 bytes

A megabyte is bytes, that is 1,048,576 bytes

A gigabyte is bytes that is 1,073,741,824 bytes

102

202

302

Signed Numbers Unsigned numbers / Signed numbers

One byte (eight bits) can be used to represent the decimal number range

0 to 255 (unsigned)

-128 to 127 (signed)

Negative binary numbers are formed by subtracting from a number one greaterthan the maximum possible (i.e 2^n or 256 for a byte)

For example,

123(D) = 01111011 (B)

-123(D) = 10000101(B) = 133(D) = (256-123)(D)

To form a two's complement number that is negative you simply takethe corresponding positive number, invert all the bits, and add 1


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Find 8 bit signed binary numbers for -35(D) ? Use direct method and 2s

complement 35(D) = 0010 0011(B)

invert -> 1101 1100(B) add 1 -> 1101 1101(B)

Golden Question:

So how can you tell the difference between:

-123(D)= 10000101(B)

and

133(D) = 10000101(B)

You cant unless you know whether youre using signedor unsignedarithmetic:

Hexadecimal Numbers

Base of 16

Six digits, 0 9 ; A F for ten fifteen

Example 70A(H) or

Convenient representation of long binaries : A series of 0,1 aresimplifed to hexa

MOV AX , 1234 has 6 HEXADIGITS ;

1670A

7B

7161 + 11160 = 123


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Conversion : Decimal to Binary

Example Converting (123)10 into binary :Division method

123 / 2 = 61 remainder 1

61 / 2 = 30 remainder 1

30 / 2 = 5 remainder 0

15 /2 = 7 remainder 1

7 /2 = 3 remainder 13 / 2 = 1 remainder 1

1 /2 = 0 remainder 1

Least significant bit(rightmost)

Most significant bit(leftmost)

Answer : (123)10 = (1111011)2

Conversion : Decimal to HexaConverting (123)10 into hex 123 16 = 7 remainder 11 (or B)

7/ 16 = 0 remainder 7

Answer : 123(D) = 7B(H)

BCD: Binary Coded DecimalsEach group of four binary bits maps on to a single hex digit. CPU uses BCD

0111 1011

7 B

1011 1001 0110 1111 1010

B 9 6 F A

E.g.


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ASCII Characters

Computers can only understand numbers :0, 1 ..

Then, how characters such as A, a , or @ is represented ?

Binary patterns are assigned to represent letters and characters

ASCII stands for American Standard Code for Information Interchange (1960)

It represent numerical numbers ( 0 9 ), alphabets ( LC , UC), symbols

Well accepted by all manufacturers

7 bit representation, 0 -> MSB : 8 bit code

ASCII Tables : see internet

A: 41(H)

a: 61(H)

Can you write a C program to convert to ACSII numbers ?

Father of Floating PointOk, have you ever thought how floating points are

stored in computers ?

Or how about complex numbers ?


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Fractional representation Fixed point representation; Limits

Floating point representation: High Precisions : very large or very small numbers

Ex:

One well accepted standard: IEEE Floating point representation

IEEE Single Precision

called "float" in the C language family, and "real" or "real*4" in Fortran. This occupies 32

bits (4 bytes) and has a significand precision of 24 bits (about 7 decimal digits).

IEEE Double Precision

called "double" in the C language family, and "double precision" or "real*8" inFortran. This occupies 64 bits (8 bytes) and has a significand precision of 53 bits

(about 16 decimal digits).

-352410X8.976910X5.675 or

Assignment No. 2

1) Write abt IEEE SP / DP

2) Hand written only

3) Elucidate (1) with 2 examples each

4) How complex is represented in IEEE single precision or double precision

5) Due Date: 12/5/2008


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IEEE Precision standard - I

3 components in IEEE Floating Pointrepresentation:

a) Sign bit 0 denotes a positive

number; 1 denotes a negative

number..b) Exponents represent both positive and negative exponents. To do this, a bias is added to the actual exponent in order to get the stored exponent. For IEEE single-precision floats, this value is 127.

- A stored value of 200 indicates an exponent of (200-127), or 73

For double precision, the exponent field is 11 bits, and has a bias of 1023.

c) Mantissa

The mantissa, also known as the significand, represents the precision bits of the number


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Little Endian and Big Endian We have seen how numbers are represented in UP. How are they stored ?

"Little Endian"

low-order byte of the number is stored i n memory at the lowest address, and the high-order byte at

the highest address. (The little end comes first.)

For example, a 4 byte LongInt :

Byte3 Byte2 Byte1 Byte0

will be arranged in memory as follows

Base Address+0 Byte0Base Address+1 Byte1

Base Address+2 Byte2Base Address+3 Byte3

"Big Endian"

means that the high-order byte of the number is stored in memory at the lowest address, and

the low-order byte at the highest address. (The big end comes first.)

Example of big endian : Sun machine, Adobe potoshop, Motorola

Example


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Little deeper

One BUS CYCLE The content of program counter initially

0000 0000 is placed on the address bus.

The instruction in this first address is 'readout of memory' and placed on the data bus

The instruction is held in the instructionregister whilst it is decoded into a signalthat goes to the control circuitry. This thencarries out the instruction.

Let us suppose the instruction was to load anumber stored in memory into theaccumulator.

The program counter increments to 00000001 the contents of this address areplaced on the data bus and the controlcircuitry loads this into the accumulator.

Example


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Program counter can have value between 0000 (h) FFFF (h)

PC value is loaded with 1400(h) , the starting address. MP is ready for execution

MP puts the values 1400 on address bus [ Read signal in on ] . PC is incremented

Content of 1400(H) is put B0(H) on data bus and send to MP

Instruction decoder decodes BO(H) - instruction is to bring 21H from address in PC.

All other registers are locked except register A

PC is set to 1402(H)

And this continues

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