A PIC16F8877 Programmer has written three different routine(s) to multiply an unsigned 3-bit number stored in a register labelled RegA by 8, and return with the product in the working register. In the particular application there is no guarantee that the upper 5 bits of RegA are clear the routine must complete within 10 instruction cycles regardless of the value in RegA Which routine should be chosen?

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A PIC16F8877 Programmer has written three different routine(s) to multiply an un...

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A PIC16F8877 Programmer has written three different routine(s) to multiply an unsigned 3-bit number stored in a register labelled RegA by 8, and return with the product in the working register.

In the particular application

there is no guarantee that the upper 5 bits of RegA are clear
the routine must complete within 10 instruction cycles regardless of the value in RegA

Which routine should be chosen?

Mul8I
      movf RegA,W
      btfsc STATUS,Z
      return
      addwf RegA,W
      addwf RegA,W
      addwf RegA,W
      addwf RegA,W
      addwf RegA,W
      addwf RegA,W
      addwf RegA,W
      return

Mul8II
      movf RegA,W
      andlw 0x07
      addwf PCL,F
      retlw 0x00
      retlw 0x08 
      retlw 0x10
      retlw 0x18 
      retlw 0x20
      retlw 0x28               
      retlw 0x30 
      retlw 0x38

Mul8III
       bcf STATUS,C
       rlf RegA,W
       bcf STATUS,C
       rlf RegA,W 
       bcf STATUS,C
       rlf RegA,W 
       return

Mul8III

There is no clear advantage offered by any of these routines.

Mul8I

Mul8II

✅

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