> While we are on this topic what it the easiest way to convert
>   movb serial_out,c  ; moves carry bit to portb pin2
...
>   BTFSC   status,carry
>   BSF     portb,pin2
>   BTFSS   status,carry
>   BCF     portb,pin2

That's a good way to do it if you can't have glitches on the output.

If glitches aren't a problem you can use this code with is one cycle faster:

   BCF     portb,pin2
   BTFSC   status,carry
   BSF     portb,pin2

In this code, if pin2 was already high, and the status was set, there would be
a two instruction cycle low glitch on pin2.

Sometimes I find it necessary in extremely time to make sure that the
transition occurs on a particular cycle regardless of the direction of the
transition.  In such cases I use code like:

   MOVF    portb,w
   ANDLW   ~(1<<pin2)
   BTFSC   status,carry
   IORLW   (1<<pin2)
   MOVWF   portb

Note that in any of these methods (even using BCF/BSF on portb directly)
there can be problems if port B has any pins configure as outputs that don't
read the same as the output latches due to external loading.

Cheers,
Eric