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Friday, April 14, 2023 80386 1
Agenda: Salient Features of 80386
Functional Block Diagram of 80836
Pin Description of 8086
Register Set of 80386
Flags
Friday, April 14, 2023 80386 2
Branch Instruction
Indirect Addressing Diagram
Address AOpcode
Instruction
Memory
Operand
Pointer to operand
Register Addressing DiagramRegister Address ROpcode
Instruction
Registers
Operand
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
Direct Addressing DiagramAddress AOpcode
Instruction
Memory
Operand
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
