On 27 Apr 2006 10:01:10 -0700, "lee" <leela2403@gmail.com> wrote:

>How does the UART know that the device connected to it is ready to
>receive data?

How about reading manuals ?

Think before ask, today: Think, Google, ask ;-)

-- 
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Use <same-name>@monlynx.de instead !

On 2006-04-27, Kurt Harders <news@kurt-harders.de> wrote:

>> How does the UART know that the device connected to it is
>> ready to receive data?

It depends on the UART.  Some don't know anything.  Some watch
the handshake lines.   Some watch for xon/xoff characters.

> It does not know anything about the connected device. The
> driver may look at the handshake lines (DTR, RTS, CTS...) but
> thats not part of the UART.

That depends on the UART.  The better UARTs do indeed look at
CTS and/or DSR, and some even monitor the receive datastream
for xon/xoff characters.

-- 
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Kurt Harders wrote:

> > How does the UART know that the device connected to it is ready to
> > receive data?
>
> It does not know anything about the connected device. The driver may
> look at the handshake lines (DTR, RTS, CTS...) but thats not part of
> the UART.

A lot of the time those handshaking signals run across the same chip
where the UART function is found.  But it's true that simple UART need
not pay attention to them - they would merely show up in registers the
host CPU could access.

With buffered UARTs though, the buffering will not do much good in a
handshaked application unless the control circuit for the buffers
monitors and drives the handshaking signals.  You could of course argue
that a buffered UART is simply a dumb UART surrounded by a buffer and
it's controller, and argue that the buffer and it's controller are
merely part of a driver transformed into hardware.

"lee" <leela2403@gmail.com> wrote in message
news:1146157270.340697.41210@u72g2000cwu.googlegroups.com...
> How does the UART know that the device connected to it is ready to
> receive data?
>

UART on what?

It doesn't.

Hi Lee,

lee wrote:

> How does the UART know that the device connected to it is ready to
> receive data?

It does not know anything about the connected device. The driver may
look at the handshake lines (DTR, RTS, CTS...) but thats not part of
the UART.

Regards, Kurt

-- 
Kurt Harders
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mailto:news@kurt-harders.de
http://www.pin-gmbh.com

"lee" <leela2403@gmail.com> wrote in message 
news:1146157270.340697.41210@u72g2000cwu.googlegroups.com...
> How does the UART know that the device connected to it is ready to
> receive data?

When does our assignement have to be handed in?

Deep.