AMD AMD-K6-2/500AFX Data Sheet - Page 47
Software Environment, AMD-K6, 2 Processor Data Sheet, FPU Control Word Register
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21850J/0-February 2000 Preliminary Information AMD-K6®-2 Processor Data Sheet The FPU control word register allows a programmer to manage the FPU processing options. Figure 13 shows the format of this register. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 YR P CC PUOZ D I MMMM MM Reserved Symbol Y RC PC PM UM OM ZM DM IM Description Bits Infinity Bit (80287 compatibility) 12 Rounding Control 11-10 Precision Control 9-8 Exception Masks Precision 5 Underflow 4 Overflow 3 Zero Divide 2 Denormalized Operation 1 Invalid Operation 0 Rounding Control Information 00b = Round to the nearest or even number 01b = Round down toward negative infinity 10b = Round up toward positive infinity 11b = Truncate toward zero Precision Control Information 00b = 24 bits Single Precision Real 01b = Reserved 10b = 53 bits Double Precision Real 11b = 64 bits Extended Precision Real Figure 13. FPU Control Word Register The FPU tag word register contains information about the registers in the register stack. Figure 14 shows the format of this register. 15 14 13 12 11 10 9 87 65 43 2 1 0 TAG TAG TAG TAG TAG TAG TAG TAG (FPR7) (FPR6) (FPR5) (FPR4) (FPR3) (FPR2) (FPR1) (FPR0) Figure 14. FPU Tag Word Register Tag Values 00 = Valid 01 = Zero 10 = Special 11 = Empty Chapter 3 Software Environment 27