[908] in linux-scsi channel archive
Re: Termination
daemon@ATHENA.MIT.EDU (Robert Nichols)
Sat Nov 9 21:38:14 1996
To: submit-linux-dev-scsi@ratatosk.yggdrasil.com
From: rnichols@interaccess.com (Robert Nichols)
Date: Fri, 8 Nov 1996 01:14:37 GMT
In article <199611051547.QAA02052@cip1.e-technik.uni-erlangen.de>,
Hartmut Niemann <niemann@cip.e-technik.uni-erlangen.de> wrote:
:> I hate to sound like an idiot here, because I'm not..
:>
:> no, really, I'm not! I work with this crap every day, my mind
:> just seems to be drawing a blank right now. I have:
:> NCR53C810-----1G_fast_scsi-II terminated scsi-id0
:> |------1G_fast_scsi-II not-terminated id1
:> |------.5G_fast_scsi-II terminated id2
:>
:> all three disks internal, nothing external (yet) they work,
:> and seem fast, I'm just unsure at this particular moment if
:
:AFAIK: no termination in id0, but termination on the NCR is
:recommended if the NCR is the last on the cable.
Correct, but make that "required," not "recommended," on the NCR. If
the cable between the NCE and the first drive is *really* short (maybe 5
inches or so), you might get away with having the termination on the
drive instead, but that's pushing your luck.
:Fast SCSI requests active termination. (Confirmation please?)
It's strongly recommended unless the bus is quite short. On a short,
internal-only bus, passive termination is usually fine (hypersensitive
Adaptec controllers might insist otherwise).
:If the NCR only offers passive termination, you probably could put
:it in the middle, if space and cable length permit:
:
: |---1G_fast_scsi-II terminated scsi-id0
: |-----NCR53C810- not terminated-
: |------1G_fast_scsi-II not-terminated id1
: |------.5G_fast_scsi-II terminated id2
:(Any comments?)
For common physical arrangements that would require a rather unusual
cable. Also, you could never use the external connector on the
NCR53C810 with that arrangement on the internal cable. That would be
making a "T", which is a *big* no-no.
If you want active termination and the NCR53C810 doesn't provide it,
another solution is to plug an active terminator onto the external
connector. That's the setup I use, since it allows me to add a device
on an external cable without having to disable any terminators inside
the box. (A few SCSI adapters will disable their onboard terminators
automatically when you plug on an external connector, but mine isn't one
of them.)
--
Bob Nichols rnichols@interaccess.com
Finger rnichols@cluster.interaccess.com for PGP public key.
PGP public key 1024/9A9C7955
Key fingerprint = 2F E5 82 F8 5D 06 A2 59 20 65 44 68 87 EC A7 D7
