>I've assumed that the 190 etc. has an internal terminator but lack proof. >Does it?
It has a "weak" termination, which is a termination caused by the 2,000 (or so) ohm equivalent internal resistance of the logic devices used to send and receive the SCSI signals.
I've never seen mention of such before; interesting..
This approach is particularly significant in a battery powered device, such as a PowerBook, where saving battery power is important.
And, "weak" termination is particularly applicable where the host-to-device cable is only an inch or two, such as in PowerBooks.
Unless we are talking apples & oranges; it is not. The SCSI cable is multiple feet long. Since the internal drive is IDE, the internal end of the chain must be the SCSI controller.
The "law" is SCSI buses have to be terminated at both ends, in order to preserve the "transmission line" characteristic impedance (about 95 ohms, IIRC) which the specification defines.
However, the "practice" is SCSI buses almost always work with only one terminator (the one at the far end), and often work with no terminators at all (save the "weak" terminations provided by the devices themselves).
SCSI & "almost always work" in the same sentence???? Are you from a parallel universe? There is a dot.sig that clearly delineates the reality I know too well:
SCSI is *NOT* magic. There are sound scientific reasons why it
is necessary to sacrifice a young goat to your SCSI chain now and then.
I will say I have had chains that would not work with one terminator, but when I had two - one in the device and the other at the jack - and it THEN worked.
-- PowerBooks 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>
PowerBooks list info: <http://lowendmac.com/lists/powerbooks.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/powerbooks%40mail.maclaunch.com/>
Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
