Hi Jim,

> Doesn't this mean that the ninth data bit would always be a stop bit?

When the UART is receiving a start code or dimmer data then the 9th data
bit would be considered one of the stop bits (and would always be a logic
high, unless a framing error occurred).  However, remember that a RESET
(or break) is defined as a high-to-low transition followed by at least 88
uS of a  logic low.  Since a start bit is also defined as a high-to-low
transition, the UART has no way of knowing if the transition it just
received is a data byte or a break.  The only difference between the two
is when the UART is expecting the stop bits.  On reception of valid data,
the stop bit (9th data bit) will be at logic high (as the UART is
expecting).  On a break, however, the stop bit (9th data bit) will be a
logic low.  This causes the UART to signal a framing error.  In my code I
simply ignored the framing error and went ahead and stored the received
9th bit.  Thus, on a break the 9th data bit will be a logic low and for
valid data will be a logic high.  As I mentioned in an earlier post,
using this method of detecting the break is not considered very reliable.
 If a REAL framing error was to occur on a data byte, my code, as written
now, would think at had received a break and would consider the next byte
as a start code, when in fact, it was dimmer data!  I am presently trying
to modify my code to use one of the timers in the PIC to determine if a
break has occurred.  This would allow for the detection of REAL framing
errors.  Once I get my code commented and more presentable, I will be
more than happy to share code snippets.  Hope this helps!  If you have
any further questions, let me know.

--------------------------------------------------------
Kelly Kohls
Amateur Radio Callsign : N5TLE
Home E-Mail Address: kkohls@juno.com
--------------------------------------------------------

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