Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!sdd.hp.com!elroy.jpl.nasa.gov!ames!dftsrv!jagubox.gsfc.nasa.gov!jim From: jim@jagubox.gsfc.nasa.gov (Jim Jagielski) Newsgroups: comp.sys.mac.hardware Subject: Terminator power: from SCSI cable or Power cable Message-ID: <5440@dftsrv.gsfc.nasa.gov> Date: 28 May 91 11:57:07 GMT Sender: news@dftsrv.gsfc.nasa.gov Reply-To: jim@jagubox.gsfc.nasa.gov (Jim Jagielski) Organization: NASA/Goddard Space Flight Center Lines: 39 I've noticed on some SCSI drives, like the 335MB Wren Runners (ST4385NM) that one can select whether you want the terminator power for that drive to come from the SCSI cable OR from the drive's own power cable. Now I know that Apple says NOT to have more than 2 sets of terminators or else you may overtax the line drivers on the SCSI chip, but what if you had these terminators powered via the power cord? For example, say you have 4 SCSI disks... ALL terminated except that disks #2 and #3 (#1 is the 1st and #4 is the last) are configured to take their termi- nator power from the wall and NOT the SCSI cable. Now would THIS configuration do any damage to the Mac (recall that as far as the Mac is concerned, it's providing term. power to only 2 sets)? Would this config. cause any SCSI communications problems (i.e. do "overterminated" SCSi lines get less reliable)? Finally, assume that you have a disk which is terminated and set up to take term. power from the wall... THEN you add an external term. block to it... What then? Finally, has anyone noticed problems with the IIfx-type terminator block? That is, can one rest assured that, assuming all else is Okay with your SCSI bus and devices, you will have no problem when you switch from the standard ext. term. block to the IIfx-type? (My question arises from the fact that my MacII is being upgraded to a IIfx. My system works fine now with the standard issue external terminators, but what will happen when I start using the IIfx-type? I'm sure that all will STILL work after all, it's just a coupla' cap's, right?) :) -- =========================================================================== #include =:^) Jim Jagielski NASA/GSFC, Code 711.4 jim@jagubox.gsfc.nasa.gov Greenbelt, MD 20771 "If we increase the size of the penguin until it is the same height as a man and then compare the relative brain size, we know find that the penguin's brain is still smaller. But, and this is the point, it is larger than it WAS!"