
MOTOROLA
1-12
OVERVIEW
RCPU
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REFERENCE MANUAL
1.3.1.1 General-Purpose Registers (GPRs)
The processor provides 32 user-level, general-purpose registers (GPRs). The
GPRs serve as the data source or destination for all integer instructions and pro-
vide addresses for all memory-access instructions.
1.3.1.2 Floating-Point Registers (FPRs)
The processor also provides 32 user-level 64-bit floating-point registers. The FPRs
serve as the data source or destination for floating-point instructions. These regis-
ters can contain data objects of either single- or double-precision floating-point for-
mats. The floating-point register file can only be accessed by the FPU.
1.3.1.3 Condition Register (CR)
The CR is a 32-bit user-level register that consists of eight four-bit fields that reflect
the results of certain operations, such as move, integer and floating-point compare,
arithmetic, and logical instructions, and provide a mechanism for testing and
branching.
1.3.1.4 Floating-Point Status and Control Register (FPSCR)
The floating-point status and control register (FPSCR) is a user-level register that
contains all exception signal bits, exception summary bits, exception enable bits,
and rounding control bits needed for compliance with the IEEE 754 standard.
1.3.1.5 Machine State Register (MSR)
The machine state register (MSR) is a supervisor-level register that defines the
state of the processor. The contents of this register are saved when an exception
is taken and restored when the exception handling completes.
1.3.1.6 Special-Purpose Registers (SPRs)
The processor provides several special-purpose registers that serve a variety of
functions, such as providing controls, indicating status, configuring the processor,
and performing special operations. Some SPRs are accessed implicitly as part of
executing certain instructions. All SPRs can be accessed by using the move to/
from special-purpose register instructions,
mtspr
and
mfspr
.
1.3.1.7 User-Level SPRs
The following SPRs are accessible by user-level software:
The link register (LR) can be used to provide the branch target address and
to hold the return address after branch and link instructions.
The count register (CTR) is decremented and tested automatically as a result
of branch-and-count instructions.
The integer exception register (XER) contains the integer carry and overflow
bits and two fields for the load string and compare byte indexed (
lscbx
) in-
struction. The XER is 32 bits wide in all implementations.
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