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section 7 - Index of

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3.4 DOUBLE PRECISION MULTIPLY MODEThe Data ALU double precision multiply operation multiplies two 48-bit operands with a96-bit result. The processor enters the dedicated Double Precision Multiply Mode whenthe user sets bit 14 (OM) <strong>of</strong> the Status Register (bit 6 <strong>of</strong> the MR register). The mode isdisabled by clearing the OM bit. For· information on the OM bit, see Section 5.4.2.13 -Double Precision Multiply Mode (Bit 14).CAUTION:While in the Double Precision Multiply Mode, only the double precision multiply algorithmsshown in Figure 3-11, Figure 3-12, and Figure 3-13 may be executed by the Data ALU;any other Data ALU operation will give indeterminate results.Figure 3-11 shows the full double precision multiply algorithm. To allow for pipelinedelay, the ANDI instruction should not be immediately followed by a Data ALU instruction.For example, the ORI instruction sets the OM mode bit, but, due to the instructionexecution pipeline, the Data ALU enters the Double Precision Multiply mode only afterX: Y:MSP1MSP2R1 •LSP1 LSP2 -... R5RODP3DP2• DP1 DPO ----ROori #$40,mr ;enter modemove x:(r1 )+,xO y:(r5)+,yO ;Ioad operandsmpy yO,xO,a x:(r1 )+,x1 y:(r5)+,y1 ;LSP*LSP-+amac x1,yO,a aO,y:(rO) ;shifted(a)+, MSP*LSP-+amac xO,y1,a ;a+LSP*MSP-+amac y1 ,x1,a aO,x:(rO)+ ;shifted(a)+, MSP*MSP-+amovea,I:(rO)+andi #$bf,mr ;exit modenon-Data ALU operation;pipeline delayFigure 3-11 Full Double Precision Multiply Algorithm

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