From: David Laight <David.Laight@ACULAB.COM>
To: 'Matthias Schiffer' <matthias.schiffer@ew.tq-group.com>,
Lukas Wunner <lukas@wunner.de>
Cc: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Jiri Slaby" <jirislaby@kernel.org>,
"Russell King" <linux@armlinux.org.uk>,
"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
"Lino Sanfilippo" <LinoSanfilippo@gmx.de>
Subject: RE: [PATCH] serial: Revert RS485 polarity change on UART open
Date: Tue, 29 Mar 2022 12:55:42 +0000 [thread overview]
Message-ID: <749eee7dd2c7464a8c4d9ea5972205fa@AcuMS.aculab.com> (raw)
In-Reply-To: <b2f29129f966685105e09781620b85c8f4f1a88e.camel@ew.tq-group.com>
From: Matthias Schiffer
> Sent: 29 March 2022 11:39
...
> I guess that would work. The fact that even the different
> variants of the 8250 are implemented inconsistently makes this
> especially ugly... It certainly puts a damper on the efforts to make
> the handling of RS485 in serial drivers more generic.
One thing to remember is that RS232 (IIRC really V.38) line driver
chips are typically inverting.
So the modem signals on a TTL level output will have the
opposite polarity to that required on the actual connector.
Normally a UART will have an 'active high' register bit for
a modem signal that drives and 'active low' pin so you get
the correct polarity with an inverting line driver.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-03-29 12:55 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-29 8:50 [PATCH] serial: Revert RS485 polarity change on UART open Matthias Schiffer
2022-03-29 10:03 ` Lukas Wunner
2022-03-29 10:39 ` Matthias Schiffer
2022-03-29 12:55 ` David Laight [this message]
2022-03-29 13:02 ` Matthias Schiffer
2022-03-29 13:19 ` David Laight
2022-03-29 13:36 ` (EXT) " Matthias Schiffer
2022-05-11 10:22 ` m.brock
2022-06-27 8:40 ` Matthias Schiffer
2022-06-29 17:01 ` Lukas Wunner
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