Hi Leonardo. Couple of academical examples more...

WBR Dmitry.

> portb   equ     0x06
> ;
>         org     0
> ;

>         movlw   b'111101111'
>         tris    portb   ;portb set to inputs except for port 4

Loop:
        rlf     PORTB,W         ;read from PORTB and shift it to W
        movwf   PORTB           ;pit it back to PORTB
        goto    Loop
;...

Loop:
        movlw   0               ;if PORTB.3=0 load W.4=0
        btfsc   PORTB,3
        movlw   0x10            ;if PORTB.3=1 load W.4=1
        movwf   PORTB
        goto    Loop
;...

> loop    btfss   portb,3 ; bit 3 high?
>         bcf     portb,4 ; if not, clear port b,4
>         btfsc   portb,3 ; bit 3 low?
>         bsf     portb,4 ; if not, set port b,4
>         goto    loop