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Instruction Set Overview
2-4
2.4
US ING T HIS MANUAL
Each instruction is detailed in Chapter 4. The following sections explain the format used
when describing each instruction.
2.4.1
Mnemonic s and Names
The primary assembly-language mnemonic and its name appear at the top of the first page
for an instruction (see Figure 2-1). Some instructions have additional mnemonics that
perform the same operation. These synonyms are listed below the primary mnemonic.
Figure 2-1
MUL
Instruc tion Mnemonic and Name S ample
Multiply Unsigned Numbers
2.4.2
Forms of the Instruction
Many instructions have more than one form. The forms for each instruction are listed in a
table just below the mnemonics (see Figure 2-2).
Figure 2-2
Instruc tion Forms T able S ample
Form
The Form column specifies the syntax for the different forms of an instruction. Each form
includes an instruction mnemonic and zero or more operands. Items in italics are
placeholders for operands that must be provided. A placeholder indicates the size and type
of operand that is allowed.
Form
Opcode
Description
Clocks
Am186 Am188
MUL r/m8
F6 /4
AX
=(r/m byte)AL
26–28/32–34
26–28/32–34
MUL
r/m16
F7
/4
DX::AX=(r/m word)AX
35–37/41–43
35–37/45–47
This operand
imm8
imm16
m
m8
m16
m16&16
m16:16
moffs8
moffs16
ptr16:16
r8
r16
r/m8
r/m16
rel8
rel16
sreg
Is a placeholder for
An immediate byte: a signed number between –128 and 127
An immediate word: a signed number between –32768 and 32767
An operand in memory
A byte string in memory pointed to by DS:SI or ES:DI
A word string in memory pointed to by DS:SI or ES:DI
A pair of words in memory
A doubleword in memory that contains a full address (segment:offset)
A byte in memory that contains a signed, relative offset displacement
A word in memory that contains a signed, relative offset displacement
A full address (segment:offset)
A general byte register: AL, BL, CL, DL, AH, BH, CH, or DH
A general word register: AX, BX, CX, DX, BP, SP, DI, or SI
A general byte register or a byte in memory
A general word register or a word in memory
A signed, relative offset displacement between –128 and 127
A signed, relative offset displacement between –32768 and 32767
A segment register