Central Processing Unit
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
3-13
floating-point value does so using the double-precision floating-point format. Therefore, 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 floating-point status and control register (FPSCR) and in some
cases, after the completion of the operation’s writeback stage, into the CR. For information on how the CR
is affected by floating-point operations, see
Section 3.7.4, “Condition Register (CR)
.”
3.7.3
Floating-Point Status and Control Register (FPSCR)
The FPSCR controls the handling of floating-point exceptions and records status resulting from the
floating-point operations. FPSCR[0:23] are status bits. FPSCR[24:31] are control bits.
FPSCR[0:12] and FPSCR[21:23] are floating-point exception condition bits. These bits are sticky, except
for the floating-point enabled exception summary (FEX) and floating-point invalid operation exception
summary (VX). Once set, sticky bits remain set until they are cleared by an mcrfs, mtfsfi, mtfsf, or mtfsb0
instruction.
summarizes which bits in the FPSCR are sticky status bits, which are normal status bits, and
which are control bits.
FEX and VX are the logical ORs of other FPSCR bits. Therefore these two bits are not listed among the
FPSCR bits directly affected by the various instructions.
MSB
0
LSB
63
FPR0
FPR1
. . .
. . .
FPR31
Reset
Unchanged
Figure 3-5. Floating-Point Registers (FPRs)
Table 3-4. FPSCR Bit Categories
Bits
Type
[0], [3:12], [21:23]
Status, sticky
[1:2], [13:20]
Status, not sticky
[24:31]
Control
Summary of Contents for MPC561
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Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
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