MPC555
/
MPC556
CENTRAL PROCESSING UNIT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
3-17
3.7.4.3 Condition Register CR
n
Field — Compare Instruction
When a specified CR field is set by a compare instruction, the bits of the specified field
are interpreted as shown in
. A condition register field can also be accessed
by the
mfcr
,
mcrf
, and
mtcrf
instructions.
3.7.5 Integer Exception Register (XER)
The integer exception register (XER) is a user-level, 32-bit register.
Table 3-8 Bit Descriptions for CR1 Field of CR
CR1 Bit
Description
0
Floating-point exception (FX) — This is a copy of the final state of FPSCR[FX] at the completion of the in-
struction.
1
Floating-point enabled exception (FEX) — This is a copy of the final state of FPSCR[FEX] at the completion
of the instruction.
2
Floating-point invalid exception (VX) — This is a copy of the final state of FPSCR[VX] at the completion of
the instruction.
3
Floating-point overflow exception (OX) — This is a copy of the final state of FPSCR[OX] at the completion
of the instruction.
Table 3-9 CR
n
Field Bit Descriptions for Compare Instructions
CR
n
Bit
1
NOTES:
1. Here, the bit indicates the bit number in any one of the four-bit subfields, CR0–CR7
Description
0
Less than, floating-point less than (LT, FL).
For integer compare instructions, (
r
A) < SIMM, UIMM, or (
r
B) (algebraic comparison) or (
r
A) SIMM, UIMM,
or (
r
B) (logical comparison).
For floating-point compare instructions, (
fr
A) < (
fr
B).
1
Greater than, floating-point greater than (GT, FG).
For integer compare instructions, (
r
A) > SIMM, UIMM, or (
r
B) (algebraic comparison) or (
r
A) SIMM, UIMM,
or (
r
B) (logical comparison).
For floating-point compare instructions, (
fr
A) > (
fr
B).
2
Equal, floating-point equal (EQ, FE).
For integer compare instructions, (
r
A) = SIMM, UIMM, or (
r
B).
For floating-point compare instructions, (
fr
A) = (
fr
B).
3
Summary overflow, floating-point unordered (SO, FU).
For integer compare instructions, this is a copy of the final state of XER[SO] at the completion of the in-
struction.
For floating-point compare instructions, one or both of (
fr
A) and (
fr
B) is not a number (NaN).
XER
— Integer Exception Register
SPR 1
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
SO
OV
CA
Reserved
BYTES
RESET:
U
U
U
U
U
U
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
U
U
U
U
U
U
U
F
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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