Motorola MPCxxx INSTRUCTION SET
1
MPCxxx Instruction Set
This chapter lists the MPCxxx instruction set in alphabetical order by
mnemonic
. Note that
each entry includes the instruction formats and a quick reference ‘legend’ that provides
such information as the level(s) of the PowerPC architecture in which the instruction may
be found—
user instruction set architecture (UISA)
,
virtual environment architecture
(VEA)
, and
operating environment architecture (OEA)
; and the privilege level of the
instruction—user- or supervisor-level (an instruction is assumed to be user-level unless
the legend specifies that it is supervisor-level); and the instruction formats. The format
diagrams show, horizontally, all valid combinations of instruction fields.
Note that the
architecture
specification refers to user-level and supervisor-level as
problem state and privileged state, respectively.
Instruction Formats
Instructions are four bytes long and
word
-aligned, so when instruction addresses are
presented to the processor (as in branch instructions) the two low-order bits are ignored.
Similarly, whenever the processor develops an instruction address, its two low-order bits
are zero. Bits 0–5 always specify the
primary opcode
. Many instructions also have an
extended opcode
. The remaining bits of the instruction contain one or more fields for the
different instruction formats.
Some instruction fields are reserved or must contain a predefined value as shown in the
individual instruction layouts. If a
reserved field
does not have all bits
cleared
, or if a field
that must contain a particular value does not contain that value, the instruction form is
invalid.
Split-Field Notation
Some instruction fields occupy more than one contiguous sequence of bits or occupy a
contiguous sequence of bits used in permuted order. Such a field is called a split field.
Split fields that represent the concatenation of the sequences from left to right are shown
in lowercase letters. These split fields— spr,
and tbr—are described in Table 1.
Table 1. Split-Field Notation and Conventions
Field Description
spr (11–20) This field is used to specify a special-purpose register for the
mtspr
and
mfspr
instructions.
tbr (11–20) This field is used to specify either the time base lower (TBL) or time base upper (TBU).
