jfs@ih1ap.UUCP (10/28/87)
> > In article <152@westmark.UUCP> dave@westmark.UUCP (Dave Levenson) writes: > >In article <1469@chinet.UUCP>, randy@chinet.UUCP (Randy Suess) writes: > >> How do you handle the problems of the 3b2 port drivers > >> requiring CD (pin 8) to be hi to dial out, and the needs > >> of the 3b2 to see CD go hi and lo for proper login/logout/hangup? > > > >This problem exists on other versions of UNIX, also. The best > >solution I have found is to use the Microcom AX/... series of > >modems. (Others may also have the feature I like). > > > 3) CD mostly asserted, but lowered for 1 second on disconnect. > > Steebek Modems (or Doughty) also have this sensible feature. They're sold > under the Steebek name and badge engineered by everyone and his brother in > the U.K. (the Quatro is quite popular, zillions of features, multiple speeds > and the neat DCD trick). > Steebek isn't the only modem with this feature. In a sense this is a plug. All of the autodialing AT&T modems (2212C, 2224B, 4024) I've played with behave similarly. Essentially they have several modes or states. Not having any modem docs on hand I'll call these modes: interactive, idle, and data. Here's a simplified description of these modem's mode dependent DCD behavior. Call it DCD or DCD or RLSD or CF, we're talking EIA pin 8 here. DCD is continuously asserted while in interactive and idle modes. Assertion of DTR and a carriage return by the DTE moves the modem from idle to interactive mode. In interactive mode the modem accepts, as you'ld expect, either administrative commands or a dial string to originate a call. After placing a call and sensing "carrier" from the answering modem the originating AT&T modem enters its data mode (8-bit transparent if you desire). In data mode the DCD signal reflects the state of the connection. If "carrier" is lost (hangup, long space disconnect, wire cutters, etc.) DCD is dropped until the modem enters idle mode by either timing out or the DTE toggles DTR. This is the way Unix likes it (System V anyway). -- Jesse Fred Shumway [ihnp4]!ih1ap!jfs (312) 510-7880