Neil
I've also seen a hardware solution  where the TX line from the
processor is used to trigger a fast-attack switch to turn the TX on
when it detects the start bit. It includes slow decay that delays the
TX disable for about one byte length. The top speed is limited by the
attack time but it was working fine at 38400b/s although the start bit
gets truncated by a uS or so.

RP

On 15/06/07, Neil Baylis <neil.baylis@gmail.com> wrote:
> Oh yes, I see now. Unfortunately, it doesn't generate an interrupt.
> It's going to set about 100 usec after the last interrupt. (I'm doing
> 115200 Baud). That's too long to just spin and wait. (My nodes are
> pretty busy).
>
> But the receiver (who's going to send the next message) does get an
> interrupt, and will be putting something on the wire very quickly,
> within a few microseconds.
>
> It's looking like a timer of about 100 usec is the best option. I
> would start the timer when I get the interrupt for the last
> transmitted byte, and disable the transmitter when the timer expires.
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