From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Edwards Subject: Re: [PATCH] Documentation about RS485 serial communications Date: Tue, 19 Oct 2010 17:22:32 +0000 (UTC) Message-ID: References: <20100408111310.524f7354@lxorguk.ukuu.org.uk> <4CBD8EE4.5040808@evidence.eu.com> <201010191727.53314.alexander.stein@systec-electronic.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org List-Id: linux-serial@vger.kernel.org On 2010-10-19, Alexander Stein wrote: > On Tuesday 19 October 2010, 16:29:48 Grant Edwards wrote: >> On 2010-10-19, Claudio Scordino 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. Yes, the AT91 UARTs do have a built-in half-duplex mode that will automatically control line direction by toggling RTS. That can used to control external half-duplex hardware like an RS485 transceiver or any RS232-connected half-duplex device like some modems. Though the Atmel docs refer to it as "RS485 mode" there is no RS485 transceiver in the AT91 parts (AFAIK), and "RS485 mode" isn't specific to RS485 - it can be used with any external half-duplex hardware. -- Grant Edwards grant.b.edwards Yow! I Know A Joke!! at gmail.com