Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker.mit.edu!ira.uka.de!smurf!urlichs From: urlichs@smurf.sub.org (Matthias Urlichs) Newsgroups: comp.periphs.scsi Subject: Re: SCSI max length Message-ID: Date: 5 Jan 91 15:51:43 GMT References: <37560@cup.portal.com> <1991Jan04.191812.16844@scuzzy.in-berlin.de> Organization: University of Karlsruhe, FRG Lines: 44 In comp.periphs.scsi, article <1991Jan04.191812.16844@scuzzy.in-berlin.de>, src@scuzzy.in-berlin.de (Heiko Blume) writes: < < Host <-SingleEnded-> Adapter <-Differential-> Adapter <-Single-Ended-> Device(s) I am running such a setup right now (the hard disks were too loud and got moved to the kitchen ;-) : the single-ended cables are each ~ 1.5 meters, the differential is 20 meters long. No problems. NB: The adapters should not have to be told which IDs are on what side of the bus. They can find out for themselves by watching the signals at runtime. < < tho, i'm not sure about the max length with this, if the adapters < don't have their own power supply. < If not, the adapter should have a standard power connector, just like the SCSI drives you're connecting to it. Powering anything bigger than a terminator pack off the SCSI bus probably is not a good idea. < the optimum cables are: < - 132 ohms imp. 50 cond. flat or 25 signal twisted pair cable for Single Ended < - 122 ohms imp. 50 cond. or 25 signal twisted pair cable for Differential The ohms may be important depending on how sensitive/fast your devices are. If there is a mismatch there can be echoes from the terminators, which can disrupt bus communications. < both should be shielded. < On the other hand, if radio&TV antenna and any heavy-duty applicances are sufficiently far away, you may be able to forget about the shielding. Advantages: it's cheaper if you already have flat cables lying around, and routing ribbon cables around the house may be easier than a thumb-thick 25-twister cable. Also, you can press connectors onto flat cable quick&easy (twisted cable has nontwisted sections every half meter or so for that purpose. Don't ever use nontwisted cable for the differential bus); shielded cables have to be soldered and checked, which is difficult with a long cable which has been routed through walls and whose ends you can't place next to each other any more... -- Matthias Urlichs -- urlichs@smurf.sub.org -- urlichs@smurf.ira.uka.de /(o\ Humboldtstrasse 7 - 7500 Karlsruhe 1 - FRG -- +49+721+621127(0700-2330) \o)/