Note
Depending upon the values of undefined register bits will make software
dependent upon the unspecified manner in which the 80386 handles these
bits. Depending upon undefined values risks making software incompatible
with future processors that define usages for these bits. AVOID ANY
SOFTWARE DEPENDENCE UPON THE STATE OF UNDEFINED 80386 REGISTER BITS.
the source and the left operand is the destination.
For example:
LOADREG: MOV EAX, SUBTOTAL
In this example LOADREG is a label, MOV is the mnemonic identifier of an
opcode, EAX is the destination operand, and SUBTOTAL is the source operand.
up:
Chapter 1 -- Introduction to the 80386Figure 1-1. Example Data Structure
GREATEST DATA STRUCTURE
ADDRESS
31 23 15 7 0 <--BIT
+---------------+---------------+---------------+---------------+ OFFSET
| |28
|---------------+---------------+---------------+---------------|
| |24
|---------------+---------------+---------------+---------------|
| |20
|---------------+---------------+---------------+---------------|
| |16
|---------------+---------------+---------------+---------------|
| |12
|---------------+---------------+---------------+---------------|
| |8
|---------------+---------------+---------------+---------------|
| UNDEFINED |4
|---------------+---------------+---------------+---------------| SMALLEST
| BYTE 3 BYTE 2 BYTE 1 BYTE 0 |0 ADDRESS
+---------------+---------------+---------------+---------------+^
BYTE OFFSET---+
1.3.3 Instruction Operands
When instructions are represented symbolically, a subset of the 80386
Assembly Language is used. In this subset, an instruction has the following
format:
label: prefix mnemonic argument1, argument2, argument3
where:
1.3.4 Hexadecimal Numbers
Base 16 numbers are represented by a string of hexadecimal digits followed
by the character H. A hexadecimal digit is a character from the set (0, 1,
2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F). In some cases, especially in
examples of program syntax, a leading zero is added if the number would
otherwise begin with one of the digits A-F. For example, 0FH is equivalent
to the decimal number 15.
1.3.5 Sub- and Super-Scripts
This manual uses special notation to represent sub- and super-script
characters. Sub-script characters are surrounded by {curly brackets}, for
example 10{2} = 10 base 2. Super-script characters are preceeded by a
caret and enclosed within (parentheses), for example 10^(3) = 10 to the
third power.
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