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Hello,

I just found further sources for information about those cables.
Within the "SGI Indigo 2 Impact Workstation's Owner's Guide" the direct
pin out assignments are given, as well as serial cable assignments.
In the book "PC-Hardware Book" by "Hans-Peter Messmer", ISBN
3-89319-710-9, the assignments for PC-to-PC serial nullmodem cables are
explained, and I used both books as a source for this mail.
Because of the discussion about serial console connections and the
required cables on the "Installing NetBSD on Indigo 2"-thread, I thought
I should open a new thread and provide some knowledge on this topic as
general technical information.
Of course it is far easier to buy such cables, it is not always as cheap
as assembling them on your own, and depending on where one lives, it is
probably not possible to buy those cables. Buying such things on the
internet isn't exactly what I prefer, since more often than not
explanations of cables aren't providing the appropriate information one
needs, and when calling the sales-personal, they seldomly know better.

So here I try to provide technical information for all those, who are
interested, and for those, who want/like/need to assemble such cables on
their own, and haven't found appropriate the information yet.

Before starting, please note that the below descripted setup has not yet
been tested and verified, that it is provided with no guarantees at all,
and that I refuse any responsibility for possible damages that occurred
while using cables based on the information below. If you use the
information of this mail, YOU DO THAT AT YOUR OWN RISK!

As soon as I have all the parts I need to assemble such a cable, and as
soon as I have the time to really assemble it, I will test and verify
this. I will then write a confirmation report - or correct the errors. ;-)



<snip source="SGI Indigo 2 Impact Workstation's Owner's Guide">
Serial Devices Using a PC Adapter Cable

To use a serial device designed for use with personal computers using a
DB-9 connector, you'll need a PC adapter cable supplied by Silicon
Graphics. This adapter cable is used to convert from the PC's DB-9
pinout to the Indigo2 IMPACT workstation's DIN-8 pinout.

The cable connector pinout assignments for the PC adapter cable are
shown in Table 6-4.

Table 6-4. Cable Connector Pinout Assignments for the PC Adapter Cable

Signal description      Pin Number       Pin Number
                     DIN-8 Connector  DB-9 Connector
                         (Male)           (Male)

DTR                        1                 4
CTS                        2                 8
TXD                        3                 3
GND                        4                 5
RXD                        5                 2
RTS                        6                 7
DCD                        7                 1
DSR                        8                 6
N/C                                          9

</snip>

The Pins arranged like this on the DIN-8 Connector:

  3
6   1
7 4
8   2
  5

On the DB-9 Connector:

5
   9
4
   8
3
   7
2
   6
1

The cable described by the SGI Guide is a plain "1:1" cable. A few
changes need to be applied to get this turned into a nullmodem-cable,
which is required for a serial console connection. The Assignment I
provide below is as strictly following the RS-232C specification as
possible, i.e. that probably a few changes are still required to make
work on the SGI-side, but at least on PC-side no special drivers or
stuff is required for this to work, every simple terminal-program that
is capable of connecting to the serial port will work out of the box.

The above stated SGI-Guide said something about RS-232 and MAC SE serial
port compliance, but not exactly which one is used. It seems, the indigo
detects this and uses the right "implementation" automatically, though I
am not quite sure about this. I based the following pin assignment on
the assumption that the Indigo is capable of RS-232 serial connections:

   Pin Number       Pin Number
DIN-8 Connector  DB-9 Connector
    (Male)           (Male)

      1                 6,9
      2,6               1
      3                 2
      4                 5
      5                 3
      7                 7,8
      8                 4

A small problem might be that on Indigo-2-Side no such pins as RI or DSR
exist. According to the pin-assignment on the plain cable provided by
the SGI-Guide and the sources I found for PC-to-PC Nullmodem cables, I
simply grounded the DSR pin of the PC using pin 8 on the Indigo (NOT pin
4, according to the SGI-Guide quoted above).

>From Indigo to PC, the DTR connects to DSR and RI just as it should.

NOTICE ONCE AGAIN: This setup is yet untested. As soon as I have all the
parts I need to assemble such a cable, and as soon as I have the time to
really assemble it, I will test and verify this. I will then write a
confirmation report - or correct the errors. ;-)
Since my time is fairly limited due to work, I cannot give an estimated
time of a confirmation or correction report, but it will come.

--

MfG / Sincerely

Volkmar Seifert
Senior Consultant

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