Classes Of Instructions - Freescale Semiconductor MPC850 User Manual

• Memory synchronization instructions—These instructions are used for memory
synchronizing. See Sections 5.2.4.6 and 5.2.5.2 for more information.
• Memory control instructions—These instructions provide control of caches, and
TLBs. For more information, see Sections 5.2.5.3 and 5.2.6.3.
• System linkage instructions—For more information, see Section 5.2.6.1, "System
Linkage Instructions."
Note that this grouping of instructions does not necessarily indicate the execution unit that
processes a particular instruction or group of instructions. This information, which is useful
in taking full advantage of the MPC850's parallel instruction execution, is provided in
Chapter 8, "Instruction Set," in The Programming Environments Manual.
Integer instructions operate on word operands. The PowerPC architecture uses instructions
that are four bytes long and word-aligned. It provides for byte, half word, and word operand
loads and stores between memory and a set of 32 general-purpose registers (GPRs).
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 MPC850 instructions belong to one of the following three classes:
• Defined
• Illegal
• Reserved
Note that while the definitions of these terms are consistent among the PowerPC
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 MPC850.
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 PowerPC 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.
Chapter 5. MPC850 Instruction Set
Instruction Set Summary