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Hardware Multiplier Operation

11.2.4 Indirect Addressing of RESLO

When using indirect or indirect autoincrement addressing mode to access the result registers, At least one

instruction is needed between loading the second operand and accessing one of the result registers:

; Access multiplier results with indirect addressing

MOV #RESLO,R5 ; RESLO address in R5 for indirect

MOV &OPER1,&MPY ; Load 1st operand

MOV &OPER2,&OP2 ; Load 2nd operand

NOP ; Need one cycle

MOV @R5+,&xxx ; Move RESLO

MOV @R5,&xxx ; Move RESHI

11.2.5 Using Interrupts

If an interrupt occurs after writing OP1, but before writing OP2, and the multiplier is used in servicing that

interrupt, the original multiplier mode selection is lost and the results are unpredictable. To avoid this,

disable interrupts before using the hardware multiplier or do not use the multiplier in interrupt service

routines.

; Disable interrupts before using the hardware multiplier

DINT ; Disable interrupts

NOP ; Required for DINT

MOV #xxh,&MPY ; Load 1st operand

MOV #xxh,&OP2 ; Load 2nd operand

EINT ; Interrupts may be enable before

; Process results

353

SLAU144J–December 2004–Revised July 2013 Hardware Multiplier

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