allon@SOLARVAX.UMD.EDU (08/01/89)
In Article 38747 jjs@PRC.Unisys.COM writes: >1. Must (should?) all SCSI devices on the chain be powered up when > the system is running. I had assumed this was false, now I am not so > sure. Can devices on the chain be selectively powered up in general? Well, I dunno, but some friends of mine were having a problem getting their Mac IIx to boot from the hard disk -- it didn't even recognize the disk. We even opened it up and checked that the connectors were tight. Finally, we tried turning on all the SCSI devices, the CD rom, the scanner, everything, and it worked fine. I guess the answer might be yes, at least in some cases. On the other end, I was trying to get a Mac+ to boot from one hard drive and not the other (both external). I turned one off, and it booted from the other one fine. The answer might have something to do with where the terminators are, and what the SCSI addresses are, but I don't know. Anybody know? - -= Allon =- - BLISS is ignorance ******************************************************************************** Disclaimer: I don't really think anybody here cares about my opinions, or even knows that I have any. Internet: allon@solarvax.umd.edu SPAN: UMDSW::ALLON allon@uap.umd.edu UMDUAP::ALLON ********************************************************************************
teener@apple.com (Michael Teener) (08/01/89)
Here is some useful information for SCSI configuration problems: 1) the Mac+ does not have any internal termination for SCSI. 2) the MacSE and MacII only have termination for SCSI *if* there is an internal hard disk. 3) you are required to have at least one termination for SCSI. 4) you are required to have two terminations for SCSI (one on each end of the bus) if there is more than one SCSI peripheral device (we get to cheat ... a Mac without an internal drive does not count as a SCSI device). 5) all of our (Apple) external peripherals do not include terminations. 6) you are allowed to leave all devices powered down *EXCEPT* the devices with attached terminations. What all this means is: (1) put a device you will always want powered on at the far end of the SCSI chain *and attach a terminator* and (2) if you do not have an internal drive do the same for the first peripheral device (terminator + always powered on). Apple has a handy little book that comes with the SCSI cables: "Apple SCSI Cable System". It contains all this info plus a lot more. (Note: if you have non-Apple peripherals then there is no guarantee that terminators follow our philosophy ... read the manual and note any comments about termination and power-on requirements.) Good luck. ---- Michael Teener -- 408-974-3521 ---------------------------------+ ---- Internet teener@apple.com, AppleLink TEENER1 | ---- Apple may know my opinions, but *I* am responsible for them | ---------------------------------------------------------------------+ Transportation by Cheetah N9900U, a loyal beast for the past 5 years.
levin@bbn.com (Joel B Levin) (08/01/89)
In article <3262@internal.Apple.COM> teener@apple.com (Michael Teener) writes: |Here is some useful information for SCSI configuration problems: . . . |What all this means is: (1) put a device you will always want powered on |at the far end of the SCSI chain *and attach a terminator* and (2) if you |do not have an internal drive do the same for the first peripheral device |(terminator + always powered on). . . . |(Note: if you have non-Apple peripherals then there is no guarantee that |terminators follow our philosophy ... read the manual and note any |comments about termination and power-on requirements.) I have just been through some of this, and can concur. I have an SE with internal HD and have just attached an external foreign drive. The new drive comes with terminators, and there is a jumper to select whether the terminators receive power from the drive or from the SCSI cable. Currently they are powered from the drive; when that is turned off the SCSI bus is dead and the Mac will only boot from and recognize floppies. Unfortunately, I am told, neither the SE nor the Plus puts terminator power out on the cable (possibly because there are fewer pins at the Mac end), so changing the jumper would be worse; then the terminators would never get power. So I have to live with disconnecting the drive from the bus if I wish to run with it powered down. /JBL = UUCP: levin@bbn.com (new) or {backbone}!bbn!levin (old) INTERNET: levin@bbn.com POTS: (617) 873-3463 "The night was"