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INTEL P INSTRUCTIONENCODING AND

DECODING

Micro 133: Microprocessor Systems

Prelim Lecture 5

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IntroductionIntel P Instruction Encoding and Decoding

Machine LanuaeIt is the native binary code that the microprocessor understand.

A!!e"#$erIt is use to translate assembly instruction to a machine code.

O%code &O%eration Code'Selects the operation performed by the microprocessor such as M!" #DD" I$%" &MP" ' etc.

It is either one or t(o byte in length for most machine language instruction.

Decodin

It is a processes representing entire assembly instruction as a binary value or he)adecimalformat *human perspective+

EncodinIt is the process of converting he)adecimal format to assembly language *machine

perspective+

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(iure 1, -he format of the /0 , /10 Instruction a+203bit instruction" b+ 43bit instruction

)*)+ , )*-)+ In!truction (or"atIntel P Instruction Encoding and Decoding

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(iure ., /6/0 Instruction 7ormat

)*))/)*)+ In!truction (or"atIntel P Instruction Encoding and Decoding

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In!truction!consist of8operation *opcode+ e.g. M!

operands *number depends on operation+

O%erand!specified using addressing modes

Addre!!in "odemay include addressing

information9egisters

%onstant values

!ariable

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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Encodinof instruction must includes8pcode

perands

#ddressing information

Encodin is processrepresenting entire instruction as a#inar2a$ue$umber of bytes needed depends on ho( much information must be

encoded .

Instructions are encoded by a!!e"#$er:O45file *lin:" then loaded by loader+

Instructions are decodedby processor during e)ecution cycle

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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O2erride Pre6i7e!It is the first bytes of a 43bit instruction format

-hese bytes are not al(ays used

Divided in -(o Parts8Addre!! Si8e, modifies the si;e of the address

used the instruction and this byte is e

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O%erand Si8e3 modifies the si;e of theregister.If the /406/10 is operating as 203bit instruction

mode machine *real or protected mode+ and 43bit

instruction" byte is e

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(ir!t #te: pcode" Direction" ' =ord bitsO%code, select the operation performed by the

microprocessor *use the lists of opcodes+

Direction &D', indicates the flo( of data D > 2" data flo( from *96M+ field to 9E? field D > /" if data flo( from 9E? field to 96M field.

ord &', determine the si;e of data orregister

= > 2" 203 or 43bit data (idth *(ord or d(ord+

= > /" 3bit data (idth *byte+

Note:= bit appear in most of theinstruction but D bit mainly appears (ithM! and some other instructions.

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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Second 4te:Mode" 9egister" ' 9egister6Memory

Mode field -his field specifies the addressing modes for selected

instruction.

-his selects the type of addressing and (hether adisplacement is present or (ith the selected instruction.MD > 22" selects data addressing modes

MD > //" /2" or 2/" selects memory addressing modes

REGfield

7ield for register assignment

96M *9egister or Memory+ 7ield for register act as a memory or memory location

assignment.

;o< to Encode In!truction! a!4inar =a$ue!>Inte$ 0P In!truction Encodin and Decodin

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(iure 3, -able for MD field a+ 203bit" b+ 43bit

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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(iure -, 9E? field for (>/ ' (>2

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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(iure ?, 203 and 43bit 96M field" segment register field" and

scaled factor.

;o< to Encode In!truction! a!4inar =a$ue!>Inte$ 0P In!truction Encodin and Decodin

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Rei!ter Addre!!inIt uses the 96M field to specify a register instead of memory location

S%ecia$ addre!!in "ode!-his addressing modes occurs (henever memory data are referenced by only the

displacement mode of addressing for 203bit instructions.

M! @2///hA" DL M! $BMC" DL

MOD> // and R/M>22/

Scaled3Inde) Cyte Indicates the additional forms of scaled3inde) addressing.

ccurs (hen 96M > 2//

In!truction EncodinInte$ 0P In!truction Encodin and Decodin

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Determine the e

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?iven the follo(ing machine code *he)code+" determine the e