Tony Cianfaglione <(E-Mail Removed)> wrote:
> I have a new problem on my 6100 now relating to the scsi chain.
>
> I have a Mustek 600 II CD flatbed scanner (scsi 1), an external 1gb hard
> drive (scsi 2), an NEC external cd burner (scsi 4), a SyQuest 88mb drive
> (scsi 5) and an Iomega 100mb zip drive (scsi 6 - terminated) on the scsi
> bus (I left scsi 3 free for the internal cd rom to take - internal HD is
> scsi 0 and cpu is scsi 7) and booting up from a cold start, the computer
> will lock up partway through the boot with a 'bus error' message and
> forcing me to restart.
>
> One time I had a error #10 and restart. However, once I click on restart,
> the 6100 will boot fine with no further errors or problems.
>
> What's happening that's causing these errors? They only occur on a cold
> boot; even if I've run the computer for several hours and then shut down.
> Pressing the power button will bring mostly the bus error and one time,
> the error #-10. I know that error #-1 is when a PowerPC detects an
> non-PowerPC program and chokes on it but I don't know what an error #-10
> means.
>
> I have the scsi bus connected to a switchbox so that I can use the same
> setup with my old IIci with a simple throw of the switch.
>
This may be helpful:
Component Order in
a SCSI Chain
SCSI: science, art, or voodoo?
Sometimes getting a SCSI chain working properly seems to be more hit and
miss than science. We know the last device should be terminated, the
chain should not exceed a certain length, and every device must have a
unique ID.
But even that isn't enough to consistently build a busy SCSI chain and
have it work reliably. The actual order of devices matters, as trial and
error prove.
Keith Bumgarner of MacInformed <http://www.macinformed.com/> sent some
very helpful, but not widely known, information.
As a physicist/systems engineer who now, oddly enough, devotes full-time
to Macintosh computing, I know it is well-documented that device buffer
size is integral to determining both relative ID and positioning on a
Macintosh SCSI chain. Briefly, the Mac's hardware reset signal (pin 40)
affirms SCSI devices on any bus in the protocol as 0, 6, 5, 4, 3, 2, 1.
Given the physics of RF, the signal travels unimpeded until it hits a
capacitance change (this is termination) and then routes back on itself.
It must do so, initially, through the most stable SCSI device, this
being the one with the largest throughput buffer. Buffer sizes, in
almost 98% of the cases, can be categorized by the type of device. Fixed
media hard drives typically have the largest buffers, followed by
Winchester-type removables (SyQuest, Jaz), optical removables, streaming
tape, CD-ROM and derivatives (with the exception of the CD-R unit with a
larger stated hardware buffer), and then scanners and printers, which in
addition to very small throughput buffers, generate high levels of the
kiss-of-death to all RF devices: random electrical noise.
All this means, as Apple engineers acknowledged about 3 years ago, is
that hard drives should have higher ID numbers and live physically
farthest from the Mac on the SCSI chain, and scanners should have lower
ID numbers and live physically next to the Mac, if possible. Also, given
the Mac's aggressive SCSI standpoint (hardware reset vs. Unit
Attention), you cannot turn SCSI devices on and off without creating
directory code errors on your media. These are low-level directory
errors which affect the device partition, and, ultimately, the SCSI
driver. They are, unfortunately, not the type of directory problems
detectable by tools like Norton Utilities, but they can be determined by
using some more obscure SCSI tools and measuring instruments.
Further correspondence results in the following suggested order for
devices in a SCSI chain based on typical buffer size. This should vary
based on actual buffer sizes.
1.computer or SCSI card, ID = 0
2.scanner
3.printer
4.CD-ROM or DVD player (Apple sets ID = 3)
5.tape drives
6.CD-R, DVD-RAM (check actual buffer size, lots of variety here)
7.optical drives 8.removable media hard drives (SyQuest, Jaz, Orb,
etc.)
9.fixed media hard drives, higher capacity usually = larger buffer
The Iomega Zip drive presents a special case, mostly because it comes
with an unusual SCSI cable with DB-25 connectors on each end, making it
easiest to place as the first device in a SCSI chain. Since onboard
termination of the external 100MB Zip drive is inadequate for a long
SCSI chain, this is another reason to avoid placing a Zip drive at the
end of a multi-item SCSI chain.
This is also a very good argument against using a scanner or printer
that insists on being the last device in the SCSI chain.
Of course, you can never have all the above items in a typical Mac SCSI
chain, since the SCSI-1 protocol Apple uses for most ports only supports
seven devices.
Here's what a loaded SCSI chain might look like, based on this advice.
This assumes the computer already has an internal hard drive and CD-ROM
or DVD player.
1.scanner
2.Zip drive (unfortunately, it must be set to SCSI ID 5 or 6)
3.tape drive
4.CD-R burner, DVD-RAM, or 640MB 3.5" optical drive
5.Jaz drive
6.partitioned 9GB hard drive for mastering CDs/DVDs
If you're having SCSI problems, this advice and a little research on
actual buffer sizes may help you build a stable SCSI chain.
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