From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Tso Subject: Re: Enabling auto RS485 half-duplex control Date: Thu, 18 Dec 2008 23:10:42 -0500 Message-ID: <20081219041042.GA20215@mit.edu> References: <200812172224.13608.mfuchs@ma-fu.de> <20081218033200.GB9871@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:47142 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753455AbYLSEKq (ORCPT ); Thu, 18 Dec 2008 23:10:46 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Grant Edwards Cc: linux-serial@vger.kernel.org On Thu, Dec 18, 2008 at 03:51:36PM +0000, Grant Edwards wrote: > Yes there are. The standard is that RTS is asserted when one > whishes to transmit (and de-asserted when one has finished > transmitting). Optionally, one waits for CTS to be asserted > before transmitting. Isn't that the definition of RTS and CTS > that's in the standard? There's a standard, which is not necessarily well adhered to. Heck, full-duplex RTS/CTS standard was used by thousands if not millions of modems in flagrent violation of the RS-232 standard for some 10 years or more before TIA-232-E was released and bowed to reality. I know I received all sorts of requests for very strange implementations of half-duplex, with people sending me product specs with all manner of requirements, both in terms of which RS-232 lines were used (which may have been confusions caused by the fact that many systems ship with random and wondrous DB9->DB25 cables, or strange DTE/DCE conversion cables), but also in terms of mutually exclusive requirements in terms of minimum and maximum turnaround times. Someday when I'm board I can try to dig the requests out of the archives, but I can definitely say that people asked for very strange things, much of which was not in the standard (and as I pointed out, until 1990 traditional full-duplex RTS/CTS hardware flow control was not recognized by the RS-232 standard either). - Ted