Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!rice!sun-spots-request From: ultra!shj@ames.arc.nasa.gov (Steve Jay) Newsgroups: comp.sys.sun Subject: Re: Sun 3 console question Keywords: Hardware Message-ID: <8902240307.AA03076@macduff.ultra.com> Date: 9 Mar 89 14:08:29 GMT Sender: usenet@rice.edu Organization: Sun-Spots Lines: 58 Approved: Sun-Spots@rice.edu Original-Date: Thu, 23 Feb 89 19:07:08 PST X-Sun-Spots-Digest: Volume 7, Issue 190, message 2 of 14 The circuit to keep a Sun from halting when the console generates a break accidentally (like powering the terminal off or disconnecting the cable) was described in sun-spots v5n45, by Malcolm Harper , way back in Sep. 87. If our moderator is willing to send it out again to everyone rather than having interested parties retrieve it from the archives, I have appended it to the end of this message. I have never tried this circuit. Steve Jay domain: shj@ultra.com Ultra Network Technologies Internet: ultra!shj@ames.arc.nasa.gov 101 Daggett Drive uucp: ...ames!ultra!shj San Jose, CA 95134 408-922-0100 >Date: Fri, 25 Sep 87 17:23:06 bst >From: Malcolm Harper >Subject: Re: Sun-3 ASCII console problem (2) The circuit we use to prevent the Watchdog Reset which normally happens when the terminal is unplugged from the Sun Console port (ttya/ttyb) is as follows. To terminal To Sun pin 3 <----:-----------------------------------------------------------< pin 2 | ________ _________________ ____________ | | | | | | 2200uf 16v | :---| 470ohm |----| <- IN4002 diode |---:---| capacitor |--- pin 7 |________| |_________________| | |____________| ________ _________________ | -ve +ve | | | | | :---| 470ohm |----| <- IN4002 diode |---: | |________| |_________________| | Types of diodes and | ________ ___________________ / transistor, and values | | | b| |/c of capacitor, are not pin 2 >----+---| 4K7ohm |----| BC212L transistor | critical. | |________| |___________________|\e | _________________ \ | | | | :-----------------| IN4002 diode -> |---:-------------------> pin 3 | |_________________| | ________ _________________ | | | | | :---| 22Kohm |----| IN4002 diode -> |----------------------- pin 25 |________| |_________________| pin 7 ------------------------------------------------------------------ pin 7 We use only three wire connections, so connect pins 5, 6, 8 and 20 together at the Sun end, and appropriate control line connections at the terminal end. This circuit is permanently connected to the Sun end; any disconnection must be at the terminal end. If the terminal is unplugged, the transistor is turned on by the negative reference voltage present at pin 25 of the Sun serial port, and hence pulls pin 3 of the Sun port negative. This causes the Sun to believe there is still a terminal plugged in. Acknowledgements to Andrew Newman and Paul Williams who designed and built it.