1. Agenda:
Friday, August 22, 2014 80386
Salient Features of 80386
Functional Block Diagram of 80836
Pin Description of 8086
Register Set of 80386
Flags
1

2. Friday, August 22, 2014 80386 2

4. Branch Instruction

5. Indirect Addressing Diagram
Address AOpcode
Instruction
Memory
Operand
Pointer to operand

6. Register Addressing Diagram
Register Address ROpcode
Instruction
Registers
Operand

7. Register Indirect Addressing Diagram
Register Address ROpcode
Instruction
Memory
OperandPointer to Operand
Registers

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°MIPS: “Three-address architecture”
• Arithmetic-logic specify all 3 operands
add $s0,$s1,$s2 # s0=s1+s2
• Benefit: fewer instructions  performance
°x86: “Two-address architecture”
• Only 2 operands,
so the destination is also one of the sources
add $s1,$s0 # s0=s0+s1
• Often true in C statements: c += b;
• Benefit: smaller instructions  smaller code

9. Direct Addressing Diagram
Address AOpcode
Instruction
Memory
Operand

10. Displacement Addressing Diagram
Register ROpcode
Instruction
Memory
OperandDisplacement
Registers
Address A
+

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• In 80386 & above, extended 32-bit register
names are: EAX, EBX, ECX, EDX, ESP,
EBP, EDI, and ESI.
• 64-bit mode register names are: RAX, RBX,
RCX, RDX, RSP, RBP, RDI, RSI, and R8
through R15.
• Important for instructions to use registers that
are the same size.
– never mix an 8-bit with a 16-bit register, an 8- or
a 16-bit register with a 32-bit register
– this is not allowed by the microprocessor and
results in an error when assembled