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MPC7400 RISC Microprocessor Users Manual
Instruction Set Summary
2.3.1.3 Illegal Instruction Class
Illegal instructions can be grouped into the following categories:
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Instructions not deTned in the PowerPC architecture.The following primary opcodes
are deTned as illegal but can be used in future extensions to the architecture:
1, 5, 6, 9, 22, 56, 57, 60, 61
Future versions of the PowerPC architecture can deTne any of these instructions to
perform new functions.
Instructions deTned in the PowerPC architecture but not implemented in a speciTc
PowerPC implementation. For example, instructions that can be executed on 64-bit
PowerPC processors are considered illegal by 32-bit processors such as the
MPC7400.
The following primary opcodes are deTned for 64-bit implementations only and are
illegal on the MPC7400:
2, 30, 58, 62
All unused extended opcodes are illegal. The unused extended opcodes can be
determined from information in Section A.2, òInstructions Sorted by Opcode,ó and
Section 2.3.1.4, òReserved Instruction Class.ó Notice that extended opcodes for
instructions deTned only for 64-bit implementations are illegal in 32-bit
implementations, and vice versa. The following primary opcodes have unused
extended opcodes.
17, 19, 31, 59, 63 (Primary opcodes 30 and 62 are illegal for all 32-bit
implementations, but as 64-bit opcodes they have some unused extended opcodes.)
An instruction consisting of only zeros is guaranteed to be an illegal instruction. This
increases the probability that an attempt to execute data or memory that was not
initialized invokes the system illegal instruction error handler (a program
exception). Note that if only the primary opcode consists of all zeros, the instruction
is considered a reserved instruction, as described in Section 2.3.1.4, òReserved
Instruction Class.ó
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The MPC7400 invokes the system illegal instruction error handler (a program exception)
when it detects any instruction from this class or any instructions deTned only for 64-bit
implementations.
See Section 4.6.7, òProgram Exception (0x00700),ó for additional information about illegal
and invalid instruction exceptions. Except for an instruction consisting of binary zeros,
illegal instructions are available for additions to the PowerPC architecture.
2.3.1.4 Reserved Instruction Class
Reserved instructions are allocated to speciTc implementation-dependent purposes not
deTned by the PowerPC architecture. Attempting to execute a reserved instruction that has
not been implemented invokes the illegal instruction error handler (a program exception).