Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!bu-cs!kwe From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) Newsgroups: comp.dcom.lans Subject: Re: RTS/CTS flow control Message-ID: <32466@bu-cs.BU.EDU> Date: 7 Jun 89 16:06:21 GMT References: <5137@charon.unm.edu> <5187@b11.ingr.com> <1989Jun6.163942.15568@utzoo.uucp> Reply-To: kwe@buit13.bu.edu (Kent England) Followup-To: comp.dcom.lans Organization: Boston U. Information Technology Lines: 33 In article <1989Jun6.163942.15568@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: > >What most people mean by "RTS/CTS" flow control is using one line for flow >control in one direction and the other for the other direction. At least >that's my impression. [...] The >signals are meant for coordinating with half-duplex modems, which must >be told when to transmit and when to listen. [...] >Unless things have changed since I learned this, RTS and CTS >thus are not flow-control signals at all. Note that this is theory, as >opposed to the facts of how they are actually used by many devices... >-- I think that is about right, but since people have, over the ages, adapted RS-232 interfaces quite readily, I think it is fair to say that RTS and CTS have meaning in the context of full-duplex operation and that this is different than in the context of half-duplex operation. In the context of full duplex interfaces RTS/CTS is hardware based flow control and I know that to be true in the course of application, having used it repeatedly over the years when software flow control did not work for one reason or another. Of course, some interfaces use CTS to mean the same as CD or DSR. The vendor has to cooperate a little here. So, if you will accept this premise we can move the discussion on to the important issue of, when hardware flow control is activated, must the other side stop immediately, or should we allow the rest of the bits in the ASCII character in transit to come thru? :-) Sound like a fun problem to debug? One reason I prefer s/w flow control, the argument about stopping in the middle of a character doesn't usually arise. Kent England, Boston U