this is 2x faster (500kbps @ 4MHz) :

; serial tx
; assumes PORTB1 initially on high state

        rrf     data,w
        xorwf   data,f

        movlw   1
        xorwf   PORTB,f         ;start bit

        skpnc
         xorwf  PORTB,f         ;b0

        btfsc   data,0
         xorwf  PORTB,f         ;b1

        btfsc   data,1
         xorwf  PORTB,f         ;b2

        btfsc   data,2
         xorwf  PORTB,f         ;b3

        .
        .
        .

        nop
        bsf     PORTB,0         ;

regards,
Reggie


Marc wrote:
>
> > 9600 is near the limit for a 4 MHz oscillator.
>
> Why?
>
> You can easily send a bit each 16 XTAL cycles. At 4MHz that is 250kbps:
>
>         movlw   0               ; start
>         nop
>         nop
>         movwf   PORTB
>
>         movlw   0               ; lsb
>         btfsc   tmp,0
>         movlw   1
>         movwf   PORTB
>
>         movlw   0
>         btfsc   tmp,1
>         movlw   1
>         movwf   PORTB
>
>         movlw   0
>         btfsc   tmp,2
>         movlw   1
>         movwf   PORTB
>
>         etc