David Olson wrote:

> start   movlw   b'11111111'     ;set porta for input
>         tris    porta
>         movlw   b'11110111'     ;set bit 3 for output
>         tris    portb
>         clrf    swst            ;clear switch register

Welcome to the wonder world of PIC's!
I notice you Tris all the unused pins as inputs, did you connect them to
ground?
If not, Tris all your unused pins as outputs, and do not tie them to
ground.

There is an ongoing discussion about whether to make unused pins as
inputs and tie them to ground, or tris the pins as outputs and just let
them float. Find out what works best for you.

Also, your input pin for the switch, did you use a pull up resistor to
keep the input pin high when the switch is not made?

The rest of your code is fine. You can make the code a whole lot
shorter, but as you are still learning, I am not going to tell you,
figure it out yourself. Tip: PortA and PortB are also registers.

Quentin