Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 173

Arithmetic and logical instructions do not read or modify memory. To use the contents of a memory
location in a computation and then modify the same or another memory location, the memory contents
must be loaded into a register, modified, and then written to the target location using load and store
instructions.
The description of each instruction includes the mnemonic and a formatted list of operands. To simplify
assembly language programming, a set of simplified mnemonics (extended mnemonics in the architecture
specification) and symbols is provided for some of the frequently used instructions; see Appendix F,
"Simplified Mnemonics," in The Programming Environments Manual for a complete list of simplified
mnemonic examples.
5.2.1 Classes of Instructions
The MPC885 instructions belong to one of the following three classes:
• Defined
• Illegal
• Reserved
Note that while the definitions of these terms are consistent among the MPC8xx processors, the
assignment of these classifications is not. For example, an instruction that is specific to 64-bit
implementations is considered defined for 64-bit implementations but illegal for 32-bit implementations,
such as the MPC885.
The class is determined by examining the primary opcode and the extended opcode, if any. If the opcode,
or combination of opcode and extended opcode, is not that of a defined instruction or of a reserved
instruction, the instruction is illegal.
In future versions of the architecture, instruction codings that are now illegal may become assigned to
instructions in the architecture, or may be reserved by being assigned to processor-specific instructions.
5.2.1.1 Definition of Boundedly Undefined
If instructions are encoded with incorrectly set bits in reserved fields, the results on execution can be said
to be boundedly undefined. If a user-level program executes the incorrectly coded instruction, the resulting
undefined results are bounded in that a spurious change from user to supervisor state is not allowed, and
the level of privilege exercised by the program in relation to memory access and other system resources
cannot be exceeded. Boundedly undefined results for a given instruction may vary between
implementations, and between execution attempts in the same implementation.
5.2.1.2 Defined Instruction Class
Defined instructions are guaranteed to be supported in all MPC8xx implementations, except as stated in
the instruction descriptions in Chapter 8, "Instruction Set," in The Programming Environments Manual.
The MPC885 provides hardware support for all instructions defined for 32-bit implementations, except
floating-point instructions.
Freescale Semiconductor
MPC885 PowerQUICC Family Reference Manual, Rev. 2
MPC885 Instruction Set
5-3