Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!uflorida!gatech!cadeta!galbp!wittsend.LBP.HARRIS.COM!mhw From: mhw@wittsend.LBP.HARRIS.COM (Michael H. Warfield) Newsgroups: comp.dcom.modems Subject: Re: Modems that reset when DTR is dropped Message-ID: <6342@galbp.LBP.HARRIS.COM> Date: 21 Oct 88 19:37:17 GMT References: <1731@ddsw1.UUCP> <721@starfish.Convergent.COM> <6592@dasys1.UUCP> <318@pvab.UUCP> <2047@udccvax1.acs.udel.EDU> Sender: news@galbp.LBP.HARRIS.COM Reply-To: mhw@wittsend.UUCP (Michael H. Warfield) Distribution: na Organization: Harris/Lanier Network Knitting Circle Lines: 42 In article <2047@udccvax1.acs.udel.EDU> tboutell@vax1.acs.udel.EDU (Thomas B Boutell) writes: >That's not quite true. Many Hayes- compatible modems will reset entirely >when DTR is toggled, but the correct response is merely to break the >connection and go into command mode. The reinitialization is a nuisance >which forces most programs to tediously resend any setup commands they >had already communicated to the modem after each call. Many of these modems (including the real McCoy V series Hayes) have an option on the DTR action (&Dn). A setting of &D3 on most of these modems sets them up to reset on a true to false transition of DTR. That resets it to the settings in the non-volatile memory. All modems at my site are configured this way. This site uses dozens of modems at speeds from 1200 through 9600 baud (including both Hayes 9600 and Telebit Trailblazer). Any register setup commands which are always used should be loaded into non-volatile memory. The ability to reset the modem back to a known state by dropping DTR is an extreme blessing where the modems are shared amoung any number of applications. Auto-answer mode in particular can create a bad situation if the controlling process does nothing "overt" to reset the modem after a connection terminates. Some modems will not work reliably if not reset this way. An example is most 2400 baud modems, after being used at 1200 baud, will answer the next dial in call at 1200 baud if they are not reset. If the calling party is expecting 2400 baud, and the modems lock in at 1200, he's up the creek! I don't quite see your point when you remark that reinitialization is a "nuisance" and resending the command is "tedious". If the program is not sending the initialization sequence the modem needs it must be depending on the modem to be in a particular state. If thats the case, I hope you get some GOOD modems. Most modem handling programs generally start out their initialization sequence with ATZ (can we say reset?). Since programs rarely get annoyed ( annoying yes, annoyed no :-) ) and the programmer had to enter an explicit initialization string into the program to begin with ( unless he's a braver soul than this sysadmin ) the term nuisance hardly applies. As far as tedious is concern, even several separate commands and responses can hardly take more than a split second and programs get tired even less often than they get annoyed. The point is only marginally valid if the commands are being entered interactively but even in that case I have yet to find a modem I really trust after having DTR dropped. Michael H. Warfield (The Mad Wizard) | gatech.edu!galbp!wittsend!mhw (404) 270-2123 / 270-2098 | mhw@wittsend.LBP.HARRIS.COM An optimist believes we live in the best of all possible worlds. A pessimist is sure of it!