Date: Thu, 8 Oct 1998 08:05:30 +0200 From: J Wunsch <j@uriah.heep.sax.de> To: FreeBSD SCSI list <freebsd-scsi@FreeBSD.ORG> Subject: Re: SCSI Differential controllers Message-ID: <19981008080530.60854@uriah.heep.sax.de>
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Simon asked me to post this clarification to the mailinglist as well: -----Forwarded message from Simon Shapiro <shimon@simon-shapiro.org>----- Message-ID: <XFMail.981007204530.shimon@simon-shapiro.org> Date: Wed, 07 Oct 1998 20:45:30 -0400 (EDT) Reply-To: shimon@simon-shapiro.org Organization: The Simon Shapiro Foundation From: Simon Shapiro <shimon@simon-shapiro.org> To: Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de> Subject: Re: SCSI Differential controllers J Wunsch, On 07-Oct-98 you wrote: > As Simon Shapiro wrote: > > > Some new controllers use what is known as > > ``low voltage differential'' with means the controller (correct name is > > HBA) will ``talk'' differential to differential devices, single-ended > > to SE > > devices. > > I thought a single SE device will degrade the entire bus to SE? I > can't imagine otherwise, since this SE device grounds one half of all > the `return' signal lines on the bus. I think you are right. I only deal with these things on the HBA-Bay leg. All the bays I use are SE inside and diff outside. There is nothing on the Diff side except for boxes and DPTs. The box has this dual capacity. The DPTs are simply differential. I think the i2o (5th generation) DPTs are dual mode. > So far, i've only browsed a little through the SCSI-3 working group > documents, they speak that only devices with active (?) negation are > guaranteed to co-operate correctly with LVD, while older SE devices > might cause damage to the LVD output stages. If i understood it > correctly, all differential output stages are required to use the > DIFFSENSE line on the bus in order to detect whether an SE device has > accidentally been connected to the bus (so they can turn off their > output drivers), i assume that's also the way LVD decides in which > mode to operate. Again, you are correct. I suggest you post this to the SCSI list, so others can benefit. My rule is: Check each device, never mix modes, check each device again, then buy the disk bays from reputable source, with the disks. Solvs lots of problems :-) Simon -----End of forwarded message----- -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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