Wren IV (?cabling) Problem

[anderson at sapir.psy.jhu.edu]

I'm trying without success to attach a CDC Wren IV drive to a 4/110.  Sun
tells me that the famous pin-26 problem on 4/110's is no longer a problem
as of the rev level of my machine, and nobody's power supply appears to
have fried, so that seems not to be what's wrong.  The Sun itself doesn't
seem to be the culprit, since it recognizes a Sun SCSI shoebox snarfed
from another machine with no problem.

What happens is that when the drive is cabled to the SCSI connector on the
machine, it won't even spin up, though it does spin up when not attached
to the 4/110. Letting it spin up and then attaching it to the machine, the
Sun reports that it can't find any sd device.

One theory: the drive unit itself is cabled to its DB-50 SCSI connector
with a straight fifty-line ribbon cable. This appears to yield the
following physical arrangement of its pinouts:

 -------------------------------------------------------------
 \    49    46   43    40  ...............  10  7   4   1    /
  \                                                         /
   \     48    45   42    39 ............ 12  9   6   3    /
    \                                                     /
     \50    47   44    41  ...............  11  8   5   2/
      ---------------------------------------------------

According to Sun, however (and also according the numbers on a 50-pin
male-to-male connector I'm using between the drive and the Sun), the
physical configuration of the Sun SCSI connector has the following
pinouts:

 -------------------------------------------------------------
 \    17   16   15   14  ...............   4   3   2    1    /
  \                                                         /
   \     33   32   31   30 ...........   21  20  19  18    /
    \                                                     /
     \50   49   48   47  ...............   37  36  35  34/
      ---------------------------------------------------

If the logical interpretation of "1, 2, 3," etc. on the drive is the same
as that on the Sun, it stands to reason I need a cable to map the one onto
the other, rather than the 50-pin straight through cable I have. Does this
make sense? I'm having a hard time convincing the supplier I need a new
cable to do this, but I don't know what else to try. The drive is jumpered
to identify as drive 0 (i.e., no jumpers on the SCSI id block), to tie
ground to both signal and physical ground, and to get terminator power
from the supply in its box. As far as I can tell, these are the only
settings available to tweak, and they seem right. If my cabling theory
isn't right, what is? One (not generally very helpful or knowledgeable
seeming) person at 800-USA-4SUN suggested "the 4/110 doesn't support
embedded SCSI". Is this plausible, explanatory, and (perhaps most
important) correct?

If you're technically sophisticated about such things, it's probably quite
clear to you by now that I'm not. Help and/or advice would be very welcome
(apart, perhaps, from the suggestion that I trash the Wren and buy
something from Sun, at their prices....). Please send mail to me at the
address below (which your mailer will probably be able to find, as opposed
to my return address above). If information that looks more broadly useful
arrives, I'll summarize to Sun-Spots.

Thanks,
Steve Anderson
Cognitive Science Center
The Johns Hopkins University

<anderson at cs.jhu.edu>