
3-42
MPC561/MPC563 Reference Manual
MOTOROLA
User Instruction Set Architecture (UISA)
3.13 User Instruction Set Architecture (UISA)
3.13.1
Computation Modes
The RCPU is a 32-bit implementation of the PowerPC ISA architecture. Any reference in
the
PowerPC
ISA
architecture
books
(UISA,
VEA,
OEA)
regarding
64-bit
implementations are not supported by the core. All registers except the floating-point
registers are 32 bits wide.
3.13.2
Reserved Fields
Reserved fields in instructions are described under the specific instruction definition
sections. Unless otherwise noted, reserved fields should be written with a zero when written
and return a zero when read. Thus, this type of invalid form instructions yield results of the
defined instructions with the appropriate field zero.
In most cases, the reserved fields in registers are ignored on write and return zeros for them
on read on any control register implemented by the MPC561/MPC563. Exception to this
rule are bits [16:23] of the fixed-point exception cause register (XER) and the reserved bits
of the machine state register (MSR), which are set by the source value on write and return
the value last set for it on read.
3.13.3
Classes of Instructions
Non-optional instructions are implemented by the hardware. Optional instructions are
executed by implementation-dependent code and any attempt to execute one of these
commands causes the RCPU to take the implementation-dependent software emulation
interrupt (offset 0x01000 of the vector table).
Illegal and reserved instruction class instructions are supported by implementation-
dependent code and, thus, the RCPU hardware generates the implementation-dependent
software emulation interrupt. Invalid and preferred instruction forms treatment by the
RCPU is described under the specific processor compliance sections.
3.13.4
Exceptions
Invocation of the system software for any instruction-caused exception in the RCPU is
precise, regardless of the type and setting.
3.13.5
Branch Processor
The RCPU implements all the instructions defined for the branch processor in the UISA in
the hardware.