Re: SCSI Questions

[Wayne Stewart <waynes@telus.dotnet>]

Aaron wrote:
> I'm planning on setting up a SCSI hard drive.  I have several external
> drives, but all are in unknown operating condition, so I'm not positive
> that I'll know when I have everything set up correctly.  As such, I'm more
> than a little concerned that I get the hardware settings right!
>
> My SCSI card is one of the earlier Apple parts.  It's labelled "APPLE II
> SCSI CARD" and has a copyright date of 1986; the ROM chip is labelled
> "341-0437-A", and is copyrighted 1987.  It also has a block of eight
> jumpers, the rightmost of which (which connects pins 8 and 9) was set when
> I got it.  Otherwise, all are open.  I'd like to know what these jumpers
> do, and which need to be set, before plugging this thing in!

The jumpers are for settimg the cards SCSI ID. You would normally have
it on the far right jumpers(8&9)

> Also, I understand that only certain SCSI cards can handle CD-ROM drives.
> I've heard that, of Apple's SCSI cards, only the High-Speed and the
> original version Rev C were capable of CD-ROM interface.  I've also read
> that the ROM chip on this card is Rev C.  Does that designation then carry
> over to the card as well, or is a Rev C card different from an earlier one
> with a Rev C ROM?

Apple made two Apple II SCSI cards. The original one and the Hi-Speed.
The original one had 3 different ROMs depending on when it came out and
if it was updated. If you have a Rev C ROM then it doesn't much matter
when it came out. There is one variation though, some cards provide term
power. Some later cards came with this from the factory, some were
modified to provide this.
Something on the SCSI chain must supply term power. A lot of Rev C cards
do and a lot of drives do. If not then a terminator that does is easy to
find. Thet're called Acteve terminators, the diagnostic terminators also
do

> Finally, I'd like to know how many and which type of terminators I'll need
> to use, for each setup.  If I'm not mistaken, I should just need a simple
> terminator on the unused port of the hard drive, if that's all that I have
> connected to the computer, but I've read conflicting things about how to
> set terminators if I add a CD-ROM drive to that (assuming, of course, that
> my SCSI card can handle it!).  Do I use an additional pass-through
> terminator between the hard drive and the CD-ROM drive, or between the
> computer and the device closest to it on the daisy chain, or none at all?

I've generally gotten by with just a terminator on the end of the SCSI
chain. A couple times when I've had 7 SCSI devices and encountered a
glitch I've added a pass-through. You should check any SCSI devices
you're going to add to see if they're internally terminated.

SCSI is pretty robust. As long as you don't connect or disconnect
anything while the powers on you're very unlikely to do it any harm.

Wayne