80386

8.2.3.5ENCODING OF OPERATION DIRECTION

(d) FIELD

In many two·operandinstructions the d field is pres· ent to indicate which operand is considered the source and which is the destination.

dDirection of Operation

0Register/Memory <- - Register

"reg" Field Indicates Source Operand;

"mod r/m" or "mod ss index base" Indicates Destination Operand

1Register <- - Register/Memory

"reg" Field Indicates Destination Operand; "mod r/m" or "mod ss index base" Indicates Source Operand

8.2.3.6 ENCODING OF SIGN-EXTEND (s) FIELD

The s field occurs primarily to instructions with im- mediate data fields. The s field has an effect only if the size of the immediate data is 8 bits and is being placed in a 1S-bit or 32-bit destination.

s

Effect on

Effect on

Immediate Data8

Immediate Data 16132

 

 

None

None

1 Sign-Extend Data8 to Fill

None

 

1S-Bit or 32-Bit Destination

 

8.2.3.7ENCODING OF CONDITIONAL TEST (tttn) FIELD

For the conditional instructions (conditional jumps and set on condition), tttn is encoded with n indicat- ing to use the condition (n = 0) or its negation (n = 1), and ttt giving the condition to test.

Mnemonic

Condition

tttn

0

Overflow

0000

NO

No Overflow

0001

B/NAE

Below/Not Above or Equal

0010

NB/AE

Not Below/Above or Equal

0011

E/Z

Equal/Zero

0100

NE/NZ

Not EquallNot Zero

0101

BEINA

Below or EquallNot Above

0110

NBE/A

Not Below or Equal/Above

0111

S

Sign

1000

NS

Not Sign

1001

PIPE

Parity/Parity Even

1010

NP/PO

Not Parity/Parity Odd

1011

L/NGE

Less Than/Not Greater or Equal

1100

NL/GE

Not Less Than/Greater or Equal

1101

LEING

Less Than or Equal/Greater Than 1110

NLE/G

Not Less or Equal/Greater Than

1111

8.2.3.8ENCODING OF CONTROL OR DEBUG OR TEST REGISTER (eee) FIELD

For the loading and storing of the Control, Debug and Test registers.

When Interpreted as Control Register Field

eeeCode

Reg Name

000

CRO

010

CR2

011

CR3

Do not use any other encoding

When Interpreted as Debug Register Field

eeeCode

Reg Name

000

DRO

001

DR1

010

DR2

011

DR3

110

DRS

111

DR7

Do not use any other encoding

When Interpreted as Test Register Field

eeeCode

Reg Name

110

TRS

111

TR7

Do not use any other encoding

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Intel 80386 Encoding of Operation Direction, Nae, Nb/Ae, Ne/Nz, Beina, Nbe/A, Pipe, Np/Po, Nge, Nl/Ge, Leing, Nle/G, Dro