MPC555
/
MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-14
Table 3-5 FPSCR Bit Descriptions
Bit(s)
Name
Description
0
FX
Floating-point exception summary. Every floating-point instruction implicitly sets FPSCR[FX] if
that instruction causes any of the floating-point exception bits in the FPSCR to change from 0 to
1. The
mcrfs
instruction implicitly clears FPSCR[FX] if the FPSCR field containing FPSCR[FX]
is copied. The
mtfsf
,
mtfsfi
,
mtfsb0
, and
mtfsb1
instructions can set or clear FPSCR[FX] ex-
plicitly. This is a sticky bit.
1
FEX
Floating-point enabled exception summary. This bit signals the occurrence of any of the enabled
exception conditions. It is the logical OR of all the floating-point exception bits masked with their
respective enable bits. The
mcrfs
instruction implicitly clears FPSCR[FEX] if the result of the log-
ical OR described above becomes zero. The
mtfsf
,
mtfsfi
,
mtfsb0
, and
mtfsb1
instructions can-
not set or clear FPSCR[FEX] explicitly. This is not a sticky bit.
2
VX
Floating-point invalid operation exception summary. This bit signals the occurrence of any invalid
operation exception. It is the logical OR of all of the invalid operation exceptions. The
mcrfs
in-
struction implicitly clears FPSCR[VX] if the result of the logical OR described above becomes ze-
ro. The
mtfsf
,
mtfsfi
,
mtfsb0
, and
mtfsb1
instructions cannot set or clear FPSCR[VX] explicitly.
This is not a sticky bit.
3
OX
Floating-point overflow exception. This is a sticky bit.
4
UX
Floating-point underflow exception. This is a sticky bit.
5
ZX
Floating-point zero divide exception. This is a sticky bit.
6
XX
Floating-point inexact exception. This is a sticky bit.
7
VXSNAN
Floating-point invalid operation exception for SNaN. This is a sticky bit.
8
VXISI
Floating-point invalid operation exception for ×-×. This is a sticky bit.
9
VXIDI
Floating-point invalid operation exception for ×/×. This is a sticky bit.
10
VXZDZ
Floating-point invalid operation exception for 0/0. This is a sticky bit.
11
VXIMZ
Floating-point invalid operation exception for ×*0. This is a sticky bit.
12
VXVC
Floating-point invalid operation exception for invalid compare. This is a sticky bit.
13
FR
Floating-point fraction rounded. The last floating-point instruction that potentially rounded the in-
termediate result incremented the fraction. This bit is not sticky.
14
FI
Floating-point fraction inexact. The last floating-point instruction that potentially rounded the in-
termediate result produced an inexact fraction or a disabled exponent overflow. This bit is not
sticky.
[15:19]
FPRF
Floating-point result flags. This field is based on the value placed into the target register even if
that value is undefined. Refer to
for specific bit descriptions.
15
Floating-point result class descriptor (C). Floating-point instructions other than the
compare instructions may set this bit with the FPCC bits, to indicate the class of the
result.
16–19
Floating-point condition code (FPCC). Floating-point compare instructions always
set one of the FPCC bits to one and the other three FPCC bits to zero. Other
floating-point instructions may set the FPCC bits with the C bit, to indicate the class
of the result. Note that in this case the high-order three bits of the FPCC retain their
relational significance indicating that the value is less than, greater than, or equal to
zero.
16
Floating-point less than or negative (FL or <)
17
Floating-point greater than or positive (FG or >)
18
Floating-point equal or zero (FE or =)
19
Floating-point unordered or NaN (FU or ?)
20
—
Reserved
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