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IDT
Understanding the Instruction Set
79RC32355 User Reference Manual
A - 3
November 4, 2002
Notes
in Figure A.1) If such fields are set to non-zero values, the operation of the processor is UNPRE-
DICTABLE.
Figure A.1 Example of Instruction Fields
Instruction Descriptive Name and Mnemonic
The instruction descriptive name and mnemonic are printed as page headings for each instruction, as
shown in Figure A.2.
Figure A.2 Example of Instruction Descriptive and Mnemonic Name
Format Field
The assembler formats for the instruction and the architecture level at which the instruction was origi-
nally defined are given in the Format field. If the instruction definition was later extended, the architecture
levels at which it was extended and the assembler formats for the extended definition are shown in their
order of extension (for an example, see C.cond.fmt). The MIPS architecture levels are inclusive; higher
architecture levels include all instructions in previous levels. Extensions to instructions are backwards
compatible. The original assembler formats are valid for the extended architecture.
Figure A.3 Example of Instruction Format
The assembler format is shown with literal parts of the assembler instruction printed in uppercase char-
acters. The variable parts, the operands, are shown as the lowercase names of the appropriate fields. The
architectural level at which the instruction was first defined, for example “MIPS32” is shown at the right side
of the page.
Purpose Field
The Purpose field gives a short description of the use of the instruction.
Figure A.4 Example of Instruction Purpose
Description Field
If a one-line symbolic description of the instruction is feasible, it appears immediately to the right of the
Description heading. The main purpose is to show how fields in the instruction are used in the arithmetic or
logical operation.
31
26 25
21 20
16 15
11 10
6 5
0
SPECIAL
000000
rs
rt
rd
0
00000
ADD
100000
6
5
5
5
5
6
Add Word
Add
Format: ADD rd, rs rt
MIPS32
Purpose:
To add 32-bit integers. If an overflow occurs, then trap.