At 11:01 AM -0500 10/28/2002, [EMAIL PROTECTED] wrote: >Your computer is probably not seeing them because one is not terminated. >Whatever drive is physically at the end of the ribbon cable (SCSI bus), must >be terminated. The reason the end device is terminated, is to pull the >voltage all the way to the end of the ribbon cable. If more than one device >has termination, it can pull too much voltage and ruin the SCSI bus. If they >are LVD drives then you will need LVD termination.
Excess termination draws too much current and while it won't ruin the bus it can corrupt the data. Aside from the less common jumper configurations like spin-on-startup the usual jumpers you need to configure are for Termination, Termination power and Parity. On the Mac you can generally leave parity off. Newer drives tend to have a jumper for Termination Enable. Older drives have termination resistor packs that have to be installed to terminate the bus. Termination power is distinct from termination. It determines where the power for the termination comes from. On some drives it can be configured as follows: 1 Termination power from the drive 2 Termination power from the bus 3 Drive supplies termination power TO the bus 1 is the most common and is common for a drive in the computer. 2 is useful for an external drive. It allows for the drive to be turned off without disrupting the bus. 3 is normally only needed when the computer doesn't supply termination power (some PowerBooks and the Mac Plus for example). Usually the selections are designed for no jumpers in the standard configuration. Thus SCSI ID0 is no jumpers. But this isn't always the case so check the drives documentation for specifically what the jumper does on and off. > >Second, each device on the ribbon cable (SCSI bus) must have a unique ID. >Normally the boot drive will be ID 0 (no jumpers on ID0, ID1, ID2 or ID3). >The CD rom drive is usually ID 3 which would be jumpers on ID0 & ID1. The >computer is usually ID7, and there are no jumpers involved. You can get >jumpers at your local computer store that deals with SCSI drives. The tab on >the jumpers is so that you can get your itty bitty fingers on them. > >The ID jumper setup goes like this: >SCSI ID# Pin ID# (on drive) >ID0 No jumpers >ID1 Jumper on ID0 >ID2 Jumper on ID1 >ID3 Jumpers on ID0 & ID1 >ID4 Jumper on ID2 >ID5 Jumpers on ID0 & ID2 >ID6 Jumpers on ID1 & ID2 >ID7 Jumpers on ID0, ID1 & ID2 This ID is reserved for the Mac (and most other hosts) so you would never want to use it. >ID8 through ID15 is repeated but with a jumper on ID3 as well (you would use >this only if you had a scsi card that recognized ID's 8 through 15) -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting [EMAIL PROTECTED] "I'm a designated driver on the Information Super Highway" -- PCI-PowerMacs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Refurbished Drives | -- Sonnet & PowerLogix Upgrades - start at $169 | & CDRWs on Sale! | Support Low End Mac <http://lowendmac.com/lists/support.html> PCI-PowerMacs list info: <http://lowendmac.com/lists/pci-powermacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:pci-powermacs@;mail.maclaunch.com> To unsubscribe, email: <mailto:pci-powermacs-off@;mail.maclaunch.com> For digest mode, email: <mailto:pci-powermacs-digest@;mail.maclaunch.com> Subscription questions: <mailto:listmom@;lowendmac.com> Archive:<http://www.mail-archive.com/pci-powermacs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
