Register Set - IBM PowerPC 604 User Manual

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2.1.1 Register Set
The PowerPC UISA registers, shown in Figure 2-1, are user-level. The general-purpose
registers (GPRs) and floating-point registers (FPRs) are accessed through instruction
operands. Access to registers can be explicit (that is, through the use of specific instructions
for that purpose such as Move
to
Special-Purpose Register (mtspr) and Move from
Special-Purpose Register (mfspr) instructions) or implicit as part of the execution of an
instruction. Some registers are accessed both explicitly and implicitly.
The number to the right of the special-purpose registers (SPRs) indicates the number that
is used in the syntax of the instruction operands to access the register (for example, the
number used to access the integer exception register (XER) is SPR 1). These registers can
be accessed using the mtspr and mfspr instructions.
Implementation Note-The 604 fully decodes the SPR field of the instruction. If the SPR
specified is undefined, the illegal instruction program exception occurs.
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PowerPC 604 RISC Microprocessor User's Manual