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Instruction Format
An instruction format defines the layout of the bits of an instruction, in terms of its constituents parts. An instruction format must include an opcode and, implicitly or explicitly, zero or more operands. Each explit operand is referenced using one of the addressing mode that is available for that machine. The format must, implicitly or explictly, indicate the addressing mode of each operand. For most instruction sets, more than one instruction format is used. Four common instruction format are shown in the figure on the next slide .
An instruction format defines the layout of the bits of an instruction, in terms of its constituents parts. An instruction format must include an opcode and, implicitly or explicitly, zero or more operands. Each explit operand is referenced using one of the addressing mode that is available for that machine. The format must, implicitly or explictly, indicate the addressing mode of each operand. For most instruction sets, more than one instruction format is used. Four common instruction format are shown in the figure on the next slide .
Generally there is a correlation between memory transfer length and the instruction length. Either the instruction
length should be equal to the memory transfer length or one should be a multiple of the other. Also in most of the
case there is a correlation between memory transfer length and word length of the machine.
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