Hello,

On Thu, 7 Jun 2001, Matthias Buelow wrote:
> >I have found that my vs3100/38 will halt if i disconnect the terminal
> >once it is running, which is normal, but if i bring the machien up with
> >no console connected in the first place, then it will run fine without
> >one.
>
> Yeah but that is kindof annoying of course because I want to see
> it boot up properly on the terminal, and then stuff it away so that
> it doesn't require space (the machine in question is on a shelf, amongst
> others).  ATM it is connected to a friend's PC's serial port.
> Which of course is annoying aswell, since if the PC reboots, on reboot
> it'll reset the port and send a break signal aswell.  Luckily the
> machine is stable enough that such a thing does not happen too often.

Ok, my experience with serial consoles is the following:
I usually run around in a not that small data center with my Nokia 9110 to
control the serial consoles of several bigger Sun machines. I encountered the
problem that sometimes, when i pull out the connector, the machine breaks.
But if i get sure, that pins 2 and 3 are disconnected _BEFORE_ 7 (i don't
pull the connector in parallel to do this), i never have a break on the
machines. So the problem might be to break the TxD line before the GND line
from the terminal to avoid the break signal.

Breaking by powering off the terminal is an effect, which could result for
2 reasons: one is the CPU/UART crashes and sets the TxD line low to break the
machine, the other is the lack of power to keep the TxD line high enough to
avoid a break.

At home i use the best solution: a terminal server. You can use any DECserver
200 for this, connect your terminal to port 1 and connect your 7 VAXen to
the other ports. The terminal server runs all the time, but you can power
off the terminal without influencing the other ports/sessions on this.

Powering off the terminal server will result in most cases in the break
again, there are some special terminal servers with little tricks to avoid
even this effect, we looked for such hardware a time ago for out data center,
but i don't know, which manufacturer finally won the race.

But at home, i can pull out the MMJ connector of my Sun without having a break,
so this is just a bit of random, if it works or not. But the live-cycle of a
VAX usually is:

Buy it, install it, boot it... use it for several years, shut it down, give
it the next person to use it several years :) You shouldn't have this problem
too often. And the dirty method would be a pullup resistor from the RxD pin
to the power lines (5V, maybe even 12V is ok for this) of about 10 KOhms or so.

...Michael

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