From: nicolas.ferre@atmel•com (Nicolas Ferre)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] Documentation about RS485 serial communications
Date: Wed, 20 Oct 2010 09:36:36 +0200 [thread overview]
Message-ID: <4CBE9C04.7000005@atmel.com> (raw)
In-Reply-To: <i9kk4o$svc$1@dough.gmane.org>
Le 19/10/2010 19:22, Grant Edwards :
> On 2010-10-19, Alexander Stein <alexander.stein@systec-electronic•com> wrote:
>> On Tuesday 19 October 2010, 16:29:48 Grant Edwards wrote:
>>> On 2010-10-19, Claudio Scordino <claudio@evidence•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.
>
> 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.
Yes, that is a vocabulary misuse to talk about "transceiver" but the
idea of Claudio's documentation is that the USART can work in both full
and half duplex and then can comply with RS-232 and RS-485 modes like
you describe precisely in your post.
> 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.
Yes, for sure you will have to use an external transceiver.
Thanks for clarifications.
Best regards,
--
Nicolas Ferre
next prev parent reply other threads:[~2010-10-20 7:36 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-29 7:16 [PATCH] atmel_serial: Atmel RS485 support v2 Claudio Scordino
2010-03-29 19:44 ` Ryan Mallon
2010-03-30 9:07 ` Claudio Scordino
2010-03-30 19:37 ` Ryan Mallon
2010-04-08 7:58 ` Claudio Scordino
2010-04-08 9:01 ` Russell King - ARM Linux
2010-04-08 10:13 ` Alan Cox
2010-04-08 13:16 ` Claudio Scordino
2010-04-08 13:42 ` Alan Cox
2010-05-26 13:18 ` Nicolas Ferre
2010-05-27 8:37 ` Claudio Scordino
2010-05-27 9:57 ` Nicolas Ferre
2010-05-27 10:29 ` Wolfram Sang
2010-05-28 15:05 ` Claudio Scordino
2010-08-11 9:26 ` [PATCH] Documentation about RS485 serial communications Claudio Scordino
2010-08-11 10:02 ` Philippe De Muyter
2010-08-11 15:32 ` Randy Dunlap
2010-08-11 19:58 ` Claudio Scordino
2010-08-14 12:50 ` Claudio Scordino
2010-08-15 22:02 ` Randy Dunlap
2010-08-15 22:19 ` Russell King - ARM Linux
2010-10-19 12:28 ` Claudio Scordino
2010-10-19 14:29 ` Grant Edwards
2010-10-19 15:27 ` Alexander Stein
2010-10-19 17:22 ` Grant Edwards
2010-10-20 7:36 ` Nicolas Ferre [this message]
2010-10-20 8:00 ` Alexander Stein
2010-10-20 18:56 ` Alan Cox
2010-10-24 11:29 ` Claudio Scordino
2010-10-28 15:10 ` Chris Down
2010-10-28 15:31 ` Claudio Scordino
2010-10-28 16:30 ` Chris Down
2010-11-10 9:17 ` Nicolas Ferre
2010-11-10 17:28 ` Greg KH
2010-11-11 10:22 ` Claudio Scordino
2010-11-16 14:30 ` Pavel Machek
2010-11-16 15:23 ` Grant Edwards
2010-11-16 15:28 ` Alexander Stein
2010-11-16 16:13 ` Matt Schulte
2010-11-16 17:20 ` Alan Cox
[not found] ` <ibuh1v$uh6$1@dough.gmane.org>
2010-11-16 20:04 ` Alan Cox
2010-11-30 19:19 ` Pavel Machek
[not found] ` <ibubf5$ev$1@dough.gmane.org>
2010-11-16 18:41 ` Matt Schulte
2010-05-28 9:42 ` [PATCH] atmel_serial: Atmel RS485 support v2 Haavard Skinnemoen
2010-05-28 13:54 ` [PATCH] MAINTAINERS: some Atmel drivers change maintainer Nicolas Ferre
2010-05-28 13:31 ` Haavard Skinnemoen
2010-06-11 7:23 ` Nicolas Ferre
-- strict thread matches above, loose matches on Subject: below --
2010-08-11 20:23 [PATCH] Documentation about RS485 serial communications Randy Dunlap
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