linux-kernel - Re: [PATCH] Documentation about RS485 serial communications

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Message-Id: <201010191727.53314.alexander.stein@systec-electronic.com>
Date:	Tue, 19 Oct 2010 17:27:27 +0200
From:	Alexander Stein <alexander.stein@...tec-electronic.com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Grant Edwards <grant.b.edwards@...il.com>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH] Documentation about RS485 serial communications

On Tuesday 19 October 2010, 16:29:48 Grant Edwards wrote:
> On 2010-10-19, Claudio Scordino <claudio@...dence.eu.com> wrote:
> > +2. HARDWARE-RELATED CONSIDERATIONS
> > +
> > +   Some CPUs (e.g., Atmel AT91) contain a transceiver capable of working
> > both +   as RS232 and RS485.
> 
> Pardon my curiosity, but I've looked at a few AT91 parts, and I've
> never seen on with an internal transceiver -- nor does Google seem
> able to find any.
> 
> Frankly, I'd be pretty surprised, since it would be very difficult
> (fab-wise), to build a mircoprocessor with I/O cells capable of
> withstanding the voltage levels specified in RS232.
> 
> Can you specify to which parts you're referring?

I doubt the AT91 do have an internal transceiver but it has a dedicated pin 
feature (RTS or CTS or something) which can be used to switch between RS232 
and RS485 by setting a bit in the USART provided the pin is connected 
properly.

Regards,
Alexander
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