3.58MHz xtal/resonator divided down, I have used the following on a PIC:
you can compress further if code density is important. regards, Graham
Daniel.


BUZZ_TX_HOT
        BCF     _TX_SCI
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
BUZZ_TX_COLD
        BSF     _TX_SCI
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        NOP
        DECFSZ  XBITPOS,F
        GOTO    BUZZ_TX_HOT
        RETURN

Vincent Deno wrote:
>
> Can anyone recommend a part efficient way to modulate a digital signal at
> around 40kHz?
>
> Thanks,
>
> Vincentn Deno