158 AMCC Proprietary
Revision 1.02 - September 10, 2007
PPC405 Processor
Preliminary User’s Manual
Instruction bits 0 through 5 always contain the primary opcode. Many instructions have an extended opcode in
another field. The remaining instruction bits contain additional fields. All instruction fields belong to one of the
following categories:
• Defined
These instructions contain values, such as opcodes, that cannot be altered. The instruction format diagrams
specify the values of defined fields.
•Variable
These fields contain operands, such as general purpose register selectors and immediate values, that may
vary from execution to execution. The instruction format diagrams specify the operands in variable fields.
• Reserved
Bits in a reserved field should be set to 0. In the instruction format diagrams, reserved fields are shaded.
If any bit in a defined field does not contain the expected value, the instruction is illegal and an illegal instruction
exception occurs. If any bit in a reserved field does not contain 0, the instruction form is invalid and its result is
architecturally undefined. Unless otherwise noted, the execute all invalid instruction forms without causing an
illegal instruction exception.
9.3 Pseudocode
The pseudocode that appears in the instruction descriptions provides a semi-formal language for describing
instruction operations.
The pseudocode uses the following notation:
= Assignment
∧ AND logical operator
¬ NOT logical operator
∨ OR logical operator
⊕ Exclusive-OR (XOR) logical operator
+ Twos complement addition
– Twos complement subtraction, unary minus
× Multiplication
÷ Division yielding a quotient
% Remainder of an integer division; (33 % 32) = 1.
|| Concatenation
=, ≠ Equal, not equal relations
<, > Signed comparison relations
, Unsigned comparison relations
if...then...else... Conditional execution; if
condition then a else b, where a and b represent one or more pseudocode
statements. Indenting indicates the ranges of
a and b. If b is null, the else does not appear.
do Do loop. “to” and “by” clauses specify incrementing an iteration variable; “while” and “until” clauses specify
terminating conditions. Indenting indicates the scope of a loop.
leave Leave innermost do loop or do loop specified in a leave statement.
n A decimal number
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u
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u
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