Instruction Format - Motorola CPU32 Reference Manual

4.2 Instruction Format
All instructions consist of at least one word. Some instructions can have as
many as seven words, as shown in Figure 4-1. The first word of the instruction,
called the operation word, specifies instruction length and the operation to be
performed. The remaining words, called extension words, further specify the
instruction and operands. These words may be immediate operands,
extensions to the effective address mode specified in the operation word,
branch displacements, bit number, special register specifications, trap
operands, or argument counts.
15
o
OPERATION WORD
(ONE WORD, SPECIFIES OPERATION AND MODES)
SPECIAL OPERAND SPECIFIERS
(IF ANY, ONE OR TWO WORDS)
IMMEDIATE OPERAND OR SOURCE ADDRESS EXTENSION
(IF ANY, ONE TO THREE WORDS)
DESTINATION EFFECTIVE ADDRESS EXTENSION
(IF ANY, ONE TO THREE WORDS)
Figure 4-1. Instruction Word General Format
Besides the operation code, which specifies the function to be performed, an
instruction defines the location of every operand for the function. Instructions
specify an operand location in one of three ways:
• Register specification
• Effective address
• Implicit reference
A register field of the instruction contains
the number of the register.
An effective address field of the instruction
contains address mode information.
The definition of an instruction implies
the use of specific registers.
The register field within an instruction specifies the register to be used. Other
fields within the instruction specify whether the register is an address or data
register and how it is to be used. SECTION 3 DATA ORGANIZATION AND
ADDRESSING CAPABILITIES contains detailed register information.
CPU32 REFERENCE MANUAL
INSTRUCTION SET
MOTOROLA
4-3
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