> Headless Sparcstation 4
> I plugged in a null modem cable connect to a DEC vt220
> into serial a/b port of sparcstation 4 and the system
> halted. dead.
> First thing I got on the screen was the <ok> prompt.
> I rebooted system, everything OK. Did what I had to do,
> logged off and I unplugged vt220 from a/b port and the
> system halted!
> What the heck is going on here??!! I don't believe it's
> supposed to bring the system down...from a simple cable
> insertion/removal, is it? Any ideas?
The simple answer is to fake the modem conditions, just look at the
connections that your interrace has, ie v.24 signals of rs423 etc,
fake out the modem signals to high, and disable software flow control of
the terminal. Disconnect the modem control signals from the terminal.
The workstation is now not aware of the connection or disconnection of
The disable of flow control is vital as this diables the possibility of
the terminal being disconnected just after the sending of XOFF which
will eventaully crash the system, as the messages queue up
There are a number of companies that sell a kit to enable you to fake
connections, and some may have a plug that copes with these requirements
already (as this is a standard problem)
Mike Skells +44 1473 224461
The views expressed here are personal and do not represent
the views of the company that I work for