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APPENDIX B
MPC823e INSTRUCTION SET
This section lists the MPC823e instruction set in alphabetical order by mnemonic. Each
entry includes the instruction formats and a quick reference legend that provides
information, such as the level(s) of the PowerPC
be found, user- or supervisor-level (an instruction is user-level unless the legend specifies
otherwise), and the instruction formats. The format diagrams show all valid combinations of
the instruction fields. The architecture specification refers to user- and supervisor-level as
problem state and privileged state, respectively.
B.1 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, when the processor develops an instruction address, its two low-order bits are
zero. Bits 0–5 always specify the primary opcode and many instructions also have an
extended opcode. The remaining bits of the instruction contains 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.
B.2 SPLIT-FIELD NOTATION
Some instruction fields occupy more than one contiguous sequence of bits or a contiguous
sequence of bits used in permuted order. These fields are called split fields. The lowercase
split fields represent the concatenation of the sequences from left to right. For instance, spr
and tbr are shown in the following table.
FIELD
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).
Split fields that represent the concatenation of the sequences in some order, which need not
be left to right are shown in uppercase letters. For instance, MB, ME, and SH are shown in
the following table.
MOTOROLA
™
architecture in which the instruction can
DESCRIPTION
MPC823e REFERENCE MANUAL
B-1
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