You are right Bob,

Every hardware UART I've seen in the last 20 years idles high,
then goes low for a start bit (at the TTL or logic level).

A constant low on the output is a "break" condition.

Matt Pobursky
Maximum Performance Systems

On Sat, 1 Dec 2001 18:33:57 GMT, Bob Barr wrote:
>On Sat, 1 Dec 2001 09:53:07 -0500, you wrote:
>
>>If you are driving the pin high, then you have a start bit and
>>you'll
>>get a framing error until you drive it low.  If you clear the
>>framing
>>error, it will come right back unless you drive the pin low.
>>
>>If you need to drive the pin high for some reason, either turn
>>off the
>>rx interrupt, or turn off the uart rx.
>>
>>Remember that in 0-5v logic, rs-232 is not inverted, so a 1 is
>>+5v.  A
>>start bit is +5v, stop bit is 0v.
>>
>
>Are you sure about that? I think you have it backwards.
>
>All of the UART timing diagrams that I've seen in Microchip=
 docs
>show
>the idle RS-232 input as a high on the Rx pin. (See PIC16F87X,
>DS30292B, page 101, figure 10-5) The start bit is detected when
>the RX
>pin goes low. The stop bit is shown as a high.
>
>Regards, Bob
>

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