[SunRescue] Serial Port Pinouts

[David L Kindred (Dave)]

>>>>> "bobkeys" == User Bobkeys BSD Bob the old greybeard BSD freak <bobkeys at weedcon1.cropsci.ncsu.edu> writes:

    >> Earlier today someone was asking about the pin-out for the
    >> combined A/B serial ports. After deleting that message, I
    >> remembered the obvious place to look for that information:
    >> www.sunhelp.org!!!  Specifically:
    >>
    >> <http://www.sunhelp.org/faq/sunref2.html>
    >>
    >> In general, a "normal" cable will let you use the A-port.  You
    >> are usually better off with the correct splitter though, as
    >> inadvertently connecting strange things to the B-port can cause
    >> no end of grief.

    bobkeys> Thanks, that was what I was looking for.

You're welcome.  I've added some comments below, mostly for the benefit
of those with less experience with the joys of serial communications.

    bobkeys> It will use 1-8+20 or the low RS232 pins.  But, for ease, I
    bobkeys> can wire up a cable with 2/3/7 and hardware 4+5 and 6+8+20,
    bobkeys> or a standard 3 wire cable.  I still have a number of those
    bobkeys> from the old days.

    bobkeys> Normal is a misnomer.

Precisely why I put it in quotes!  The only thing truly standardized is
that you will need a custom cable for nearly every application :(

    bobkeys> Normal is the full 25, and that would not work well on the
    bobkeys> dual port thing.

It turns out that it does work a fair percentage of the time, providing
the device at the other of the cable doesn't do anything "interesting"
with the pins used by the B-port.  You're also fine if you're using a
9-25 arrangement to connect to something using the PC-style connections.

    bobkeys> Back when I was running 300 port pentel hubs in the 80's,
    bobkeys> we always used 3 wire hookups, and it always worked.

A long, long time ago, at a University not that far away, they saved
money by relying on the fact that most equipment does bond Signal Ground
to Frame Ground and connected all their terminals with 2 wire
hookups. Remarkably, it did work most of the time.

    bobkeys> Since Sun did not appear to do much to the actual pinout
    bobkeys> conventions for the low RS232, it should still work fine,
    bobkeys> as long has hardwired handshake does not present any
    bobkeys> problems in software.  At 9600 baud, I would not expect it
    bobkeys> to.

As you've mentioned, many applications don't care about the control
leads.  Generally you are better off terminating them (using the 4+5 and
6+8+20 jumpers you mentioned above).  This will allow things to work for
the few applications do do expect proper lead response (like if you're
running SunOS with it's tty/cul arrangement).

One thing you want to avoid is connecting an input to a long cable and
then not connecting it at the other end.  The earliest Sun 16-port VME
cards were particularly sensitive to this, and you could lock up the
whole system by adding an "antenna" to just one or two DCD leads.

And all of the rules change when you want to hook up a modem rather than
a terminal.  Once you want to connect a modem you want to properly
connect the control leads or you'll never get it to behave.  This is
especially true if you are using the modem for dial-in access.

    bobkeys> Now to dig out or patch up a cable, and try the SS10 on
    bobkeys> serial console.

It should work fine.  In fact, I have a stack of Classics that I've
"round-robined" the serial ports (each machines B-port goes to the next
machines A-port) so I can run them all from the first, on which I have a
Monitor/Keyboard.  Cheaper than a port switch or terminal server, and
you can also get to them remotely.

-- 
David L. Kindred                       <mailto:d.kindred at telesciences.com>
Unix Systems & Network Administrator   Telesciences, Inc.
Phone: +1 856 642 4184                 2000 Midlantic Drive, Suite 410
Fax: +1 856 866 0185                   Mount Laurel, NJ 08054 USA