MGMT 1050 Chapter Notes - Chapter 2: Operand, Opcode
MGMT 1050 Chapter 2 Notes – Summary
Introduction
Instruction word requirements and constraints
• The instruction word consists of an op code and two fields that point to registers.
• As shown, this instruction would move data from register 5 to register 10.
• Unless the operation is done in place, the sources are normally left unchanged by the
instruction, whereas the destination is almost always changed.
• The source and destination addresses may be registers or memory locations.
• Since most modern computers have multiple registers available to the user it is usually
necessary to provide at least two explicit address fields, even for an address-register
move.
• Since the number of the particular register must be specified in the instruction.
• The sources and destinations of data for an instruction, whether implicit or explicit, are
also known as operands.
• Thus, instructions that move data from one place to another have two operands
• One source operand and one destination operand.
• Arithmetic operations such as ADD and SUBTRACT require three operands.
• Explicit address fields are also known as operand fields.
• Most commonly, instructions that manipulate data will have one address field for
operations that happen in place, and two or three address fields for move and
arithmetic operations.
• On some computers one or more of the addresses may be implicit, and no address field
is required for the implicit address.
• However, in modern computers most address references are explicit, even for register
addresses, because this increases the generality and flexibility of the instruction.
• Thus, most computer instructions will consist of an op code and one, two, or three
explicit address fields.
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