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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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