PIC Microcontoller Input / Output LED Methods

Driving an LED bargraph display

From Regulus Berdin

Given a number in bin, from 1 to 30, this code will drive that number of LED's on.

; 1-30 to 30 leds 
;input:   bin 
;output:  led1,led2,led3,led4 

convert: 
        clrf    led1 
        clrf    led2 
        clrf    led3 
        clrf    led4 
        incf    bin,f 
loop: 
        decfsz  bin,f           ;do not include 0 
         goto   $+2 
        return 

        decf    bin,f 
        setc                    ;turn on led 
        rlf     led4,f 
        rlf     led3,f 
        rlf     led2,f 
        rlf     led1,f 
        goto    loop 

;-------------------- 

I have another solution, using the fact that 1-30 bar is equal to 2^y - 
1.  This routine is isochronous and faster on some values than the 
above. 

Here goes: 

convert: 
        clrf    a1 
        clrf    a2 
        clrf    a3 
        clrf    a4 

        movlw   a4              ;2^bin 
        btfsc   bin,3 
         movlw  a3 
        btfsc   bin,4 
         addlw  -2               ;corrected from 'movlw  a1' 
        movwf   FSR 

        movlw   B'00000001' 
        btfsc   bin,1 
         movlw  B'00000100' 
        movwf   INDF 

        btfsc   bin,0 
         addwf  INDF,f 

        btfsc   bin,2 
         swapf  INDF,f 

        movlw   1               ;subtract by 1 
        subwf   a4,f 
        skpc 
         subwf  a3,f 
        skpc 
         subwf  a2,f 
        skpc 
         subwf  a1,f 
 

You don't need a 30bit number just because you want to drive a 30led bar :)  All you need is a number from 0 to 30, which boils down to a simple division, if your representation is linear. 0->0%->no led, 65535->100%->all (30) leds. that's 30 intervals for 65535, hence each interval (corresponding to one led more) is 65535/30... you divide your load by this number, and get the number of leds to switch on.

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