🚀 go-pugleaf

Rebecca and Rowland <real-address-in-sig@flurbletigibbet.rhubarb.foobar>
wrote:

> > To cut a very long story short the SCSI spec states that the
> > host device (Computer) must provide a +5v line on the SCSI
> > connections to supply the terminator resistors. 
> 
> Hang on - that can't be right.  Termination resistors don't need any
> power at all.  They connect from the signal lines to a 0V line.

I'm afraid they do, I would think that you might find that the
terminator resistors are used to pull those logic lines low
and so allowing the SCSI interface to detect if the chain is proplerly
terminatored or not.

Pulling the logic line low without the resistors can be done but in 
the event you ever get a short to ground anywhere on your system
your SCSI interface is going to start drawing large emounts of
current, subbenly your Mac and external gear starts getting very
smelly, very burnt and very dead, time for a new Mac.


> > Guess what, the Mac plus doesn't supply this voltage
> > so even if you use plug terminators your SCSI chain
> > still can't figure out that anything is connected to it.
> 
> I'm using a plug terminator on the end of my Mac Plus's SCSI chain and
> it works perfectly happily.

I'll take a bet that one of your external SCSI devices has been
modifyied internally to supply the +5v line.