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assembly code help

Discussion in 'Assembly Language Programming (ALP) Forum' started by emaney, Jun 13, 2007.

  1. emaney

    emaney New Member

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    Assembly language
    i realy need somones help with this pic16f84a question
    question
    A de-multiplexer has an input line, pinRB0, and four output
    lines, output0 to output3, which are, respectively, the pins RA0-RA3. the
    demultiplexer copies the digital signal appearing on the input line on to one of
    the four output lines. The output line is selected by a two bit
    selection code input on the pins RB1 and RB2.
    end of question

    i have done the code,the following is the code, but its not right please can u help me fix it
    Code:
    #DEFINE PAGE0 BCF 0x03,5
    #DEFINE PAGE1 BSF 0x03,5
    
    PCL: EQU 0x02
    STATUS: EQU 0x03
    PORTA: EQU 0x05
    TRISA: EQU 0x05
    PORTB: EQU 0x06
    TRISB: EQU 0x06
    
    W: EQU 0
    F: EQU 1
    
    ORG 0x0
    goto MAIN
    org 5
    
    MAIN:
    clrf PORTA
    clrf PORTNB
    PAGE1
    movlw B'00000111'
    iorwf TRISA,F ;RA0-RA2 as input
    clrf TRISB ;Port B0-B7 as output
    PAGE0
    
    loop:
    
      ;get the output selector
      movf PORTB,w
      rrf WREG
      andlw B'00000011'
    
      ;convert 0-3 to bit-mask
      call table
      movwf Mask
    
      ;switch all zeroes to ones in mask and vice versa
      xorlw B'11111111',w
    
      ;read all the bits of PORTA but the selected one (leave it clear)
      andwf PORTA,w
    
      ;if PORTB.0 is set, set also selected output in PORTA
      btfsc PORTB,0
      orwf Mask,w
    
      ;write modified value back to PORTA
      movwf PORTA
      goto loop  
    
    table:
    
      addwf PCL,F
      retlw B'00000001'
      retlw B'00000010'
      retlw B'00000100'
      retlw B'00001000'
     
    Last edited by a moderator: Jun 13, 2007

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