On Thu, Apr 22, 2004 at 11:44:11AM +0800, John Niven wrote: > Yes, I understand but doesn't that mean that the motherboard already > has a terminator built in? So if I used an internal (terminated) drive, > and an external (terminated) chain, I would have: > > Term <-> drive <-> Term (MB) <-> drive <-> Term
If you pull out the power supply, you will notice a second internal SCSI connector. I believe that is for the "external" SCSI bus. If that is the case the typical setup (which would use the SCSI socket parallel to the NuBus slots) would be: term <-> drive <-> mainboard 1, mainboard 2 <-> drive <-> term In otherwords, you don't have to worry about impedence in the middle of the SCSI chain. As for termination on the mainboard, I'm not sure it is an issue. If there is a cable hanging off of it, there is probably a device attached to it, in which case it would be terminated as normal. If there isn't a device attached to the bus, there probably isn't a long transmission line attached to it either. In this case the propegation delays are probably so short that they don't create interference (any reflections would be damped at the other end of the bus) and the lines are so short that they probably wouldn't pick up much external noise. (These are idle guesses.) > I've always assumed that the MB provided the termination power. I believe the SCSI controller usually provides the termination power, but that isn't alway the case (eg. the Apple High Speed SCSI card for the Apple II). I don't know how many boards don't provide termination power. > So I still need to know if the Apple CDROM acts as a terminator, > or if I have to add a terminator to the cable. My guess would be no. I took mine apart, and didn't find any evidence of the supporting electronics (I found pads which would probably hold the electronics, but they were quite unoccupied). It does make sense: in most cases Apple would have sold these as external units, in which case external terminators or the norm; or they would have sold them as part of a system, in which case the hard drive would have provided termination. Byron. -- Vintage Macs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/vintage.macs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
