xii
M68040 USER’S MANUAL
MOTOROLA
TABLE OF CONTENTS (Continued)
Paragraph
Page
Number
Title
Number
8.4.6.5
Write-Back Address and Write-Back Data ..................................... 8-26
8.4.6.6
Push Data ...................................................................................... 8-27
8.4.6.7
Access Error Stack Frame Return From Exception ....................... 8-27
Section 9
Floating-Point Unit (MC68040 Only)
9.1
Floating-Point Unit Pipeline ...................................................................9-1
9.2
Floating-Point User Programming Model .............................................. 9-2
9.2.1
Floating-Point Data Registers (FP7–FP0) ......................................... 9-2
9.2.2
Floating-Point Control Register (FPCR) ............................................ 9-3
9.2.2.1
Exception Enable Byte ...................................................................9-3
9.2.2.2
Mode Control Byte ......................................................................... 9-3
9.2.3
Floating-Point Status Register (FPSR) ..............................................9-4
9.2.3.1
Floating-Point Condition Code Byte............................................... 9-4
9.2.3.2
Quotient Byte ................................................................................. 9-5
9.2.3.3
Exception Status Byte.................................................................... 9-5
9.2.3.4
Accrued Exception (AEXC) Byte. .................................................. 9-5
9.2.4
Floating-Point Instruction Address Register (FPIAR) ........................ 9-6
9.3
Floating-Point Data Formats and Data Types....................................... 9-7
9.4
Computational Accuracy ....................................................................... 9-11
9.4.1
Intermediate Result ........................................................................... 9-12
9.4.2
Rounding the Result .......................................................................... 9-13
9.5
Postprocessing Operation..................................................................... 9-15
9.5.1
Underflow, Round, Overflow ............................................................. 9-16
9.5.2
Conditional Testing ............................................................................9-16
9.6
Floating-Point Exceptions ..................................................................... 9-20
9.6.1
Unimplemented Floating-Point Instructions....................................... 9-20
9.6.2
Unsupported Floating-Point Data Types ...........................................9-22
9.7
Floating-Point Arithmetic Exceptions ....................................................9-24
9.7.1
Branch/Set on Unordered (BSUN) ....................................................9-25
9.7.1.1
Maskable Exception Conditions..................................................... 9-26
9.7.1.2
Nonmaskable Exception Conditions .............................................. 9-27
9.7.2
Signaling Not-a-Number (SNAN)....................................................... 9-27
9.7.2.1
Maskable Exception Conditions..................................................... 9-27
9.7.2.2
Nonmaskable Exception Conditions .............................................. 9-27
9.7.3
Operand Error ................................................................................... 9-28
9.7.3.1
Maskable Exception Conditions..................................................... 9-29
9.7.3.2
Nonmaskable Exception Conditions .............................................. 9-30
9.7.4
Overflow ............................................................................................ 9-31
9.7.4.1
Maskable Exception Conditions..................................................... 9-31
9.7.4.2
Nonmaskable Exception Conditions .............................................. 9-31
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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