elel@cbnewsd.att.com (eric.edberg) (01/12/90)
Our Sun hosts (or rather some of them) are connected to ASCII terminals rather than the typical Sun console. A well known problem occures if the BREAK key is depressed or the terminal is powered down: the system will crash. At one time I heard someone talk about a fix (circuit board) that might prevent the crashes from occuring. Does such a device exist ?? Is there really a solution to this problem ?? Just checking for solutions. Please post results as many would be interested. Eric Edberg att!ihlpa!elel att!iexist!elel (708)713-5231
beau@uunet.uu.net (01/30/90)
In article <4335@brazos.Rice.edu> elel@cbnewsd.att.com (eric.edberg) writes: >X-Sun-Spots-Digest: Volume 9, Issue 10, message 17 of 22 > >Our Sun hosts (or rather some of them) are connected to ASCII terminals >rather than the typical Sun console. A well known problem occures if the >BREAK key is depressed or the terminal is powered down: the system will >crash. At one time I heard someone talk about a fix (circuit board) that >might prevent the crashes from occuring. Does such a device exist ?? Is >there really a solution to this problem ?? Just checking for solutions. >Please post results as many would be interested. The system does NOT crash. The BREAK key on an ASCII console, powering UP (not down) an ASCII console, and plugging IN the Sun keyboard (not unplugging) all have the same effect. These actions cause the serial input chip to detect a framing error on the serial input line, and report that to the kernel with an interrupt. The serial port driver for the console serial port treats a framing error as equivalent to the "L1-a" combination on the Sun keyboard. The driver aborts Unix (SunOS) and transfers control to the PROM monitor. (The "L1-a" combination is actually detected by the keyboard driver, one level higher.) At that point, one can continue the system using the "c" PROM monitor command. While it's easy to recover from the situation, the power-on part can be annoying. One "fix" for that is to install a small resistor (about 4.5k, 1/4-watt) between ground and receive data pin inside the terminal cable connector, at the CPU end of the cable. This "fix" also works to eliminate the noise that causes garbage logins to appear, when a very long terminal cable runs out to a powered-down ASCII terminal. -- Beau James beau@Ultra.COM Ultra Network Technologies {sun,ames}!ultra.com!beau
perl@uunet.uu.net (Robert Perlberg) (02/02/90)
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 <mkh%prg.oxford.ac.uk@nss.cs.ucl.ac.uk>, 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 <mkh%prg.oxford.ac.uk@nss.cs.ucl.ac.uk> >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.