MPC555
/
MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-12
3.7.1 General-Purpose Registers (GPRs)
Integer data is manipulated in the integer unit’s thirty-two 32-bit GPRs, shown below.
These registers are accessed as source and destination registers through operands
in the instruction syntax.
3.7.2 Floating-Point Registers (FPRs)
The PowerPC architecture provides thirty-two 64-bit FPRs. These registers are ac-
cessed as source and destination registers through operands in floating-point instruc-
tions. Each FPR supports the double-precision, floating-point format. Every instruction
that interprets the contents of an FPR as a floating-point value uses the double-preci-
sion floating-point format for this interpretation. That is, all floating-point numbers are
stored in double-precision format.
All floating-point arithmetic instructions operate on data located in FPRs and, with the
exception of the compare instructions (which update the CR), place the result into an
FPR. Information about the status of floating-point operations is placed into the float-
ing-point status and control register (FPSCR) and in some cases, into the CR, after the
completion of the operation’s writeback stage. For information on how the CR is affect-
ed by floating-point operations, see
3.7.3 Floating-Point Status and Control Register (FPSCR)
The FPSCR controls the handling of floating-point exceptions and records status re-
sulting from the floating-point operations. FPSCR[0:23] are status bits. FPSCR[24:31]
are control bits.
GPRs
— General-Purpose Registers
MSB
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
LSB
31
GPR0
GPR1
. . .
. . .
GPR31
RESET: UNCHANGED
FPRs
— Floating-Point Registers
MSB
0
LSB
63
FPR0
FPR1
. . .
. . .
FPR31
RESET: UNCHANGED
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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