On Wed, 30 Apr 2003, Olin Lathrop wrote:

> The TRMT flag tells you that the whole byte has actually been sent on the
> wire.

No, it does not.  It tells you that the transmit shift register is
empty.  It does not mean the UART has finished transmitting it on the
wire.

> Most of the time you don't care, but it can be important to know if
> the wire is being shared.  I've only used the TRMT flag twice that I can
> remember.  Once was when the UART was connected to a RS-485 bus.  The
> firmware had to know when the last packet byte was actually sent before
> reversing the bus driver hardware from transmit to receive.

In both of these situations, you might have triggered framing errors
at the receiver by relying on TRMT.

--
John W. Temples, III

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