Re: 2.5 SCSI Drive?

[dempson@actrix.gen.nz (David Empson)]

In article <3210AF93.D73@monmouth.com>, Daniel Webster
<dwebster@monmouth.com> wrote:

>Greetings!
>I am trying to use a 2.5 SCSI drive with My GS.  I used to use the drive 
>with a powerbook, as an external 40.  Its in an external case which is 
>powered via the ADB port, and has a DB 25 through connector for the SCSI 
>port.  The ID is externally selectable.  I have manged to get the GS to 
>see it when I use it as part of a SCSI chain (ie with another drive)  I 
>loaded the Sys on it, but by itself the GS will not see it (even with a 
>terminator attached to the port) 

The problem is most likely to be lack of termination power.  The drive
probably doesn't supply power for terminators, assuming the computer will
do so (as most Macs do, and many external hard drives for the IIgs).

If you have an Apple SCSI card, it does not provide termination power
unless it has been modified (this modification was pre-installed on recent
Apple High-Speed SCSI cards).  The RamFast can optionally supply
termination power.

The problem with supplying termination power from the Apple IIgs is that
it imposes quite a lot of extra load on the computers power supply.  In
theory, termination power supply requires up to 480 mA to be supplied by
the computer.

The documented limit for power supply on the 5V rail for ALL slots is 500
mA, so if the computer is supplying termination power, there is no spare
capacity for any cards that are installed (including the SCSI card which
is supplying termination power!)

Similarly, the Apple Desktop Bus has a documented limit of 500 mA for all
devices.  The keyboard and mouse probably use something in the region of
100 to 200 mA.  If another area of the computer is drawing too much power,
less capacity will be available on the ADB.

It sounds like your other hard drive IS supplying termination power, so
they work when both are plugged in.


The crash-on-boot problem is harder to explain.  One thought that comes to
mind is that the IIgs may not be able to provide sufficient power for the
drive.  Can you try powering it from a different computer while running it
on the IIgs?

Another possible problem (if you have an Apple SCSI card) is a poor SCSI
implementation in the drive.  The initial phase of the GS/OS boot is
performed using the SCSI card's firmware.  A short time after the GS/OS
splash screen is displayed, the GS/OS SCSI manager is loaded, and controls
all subsequent SCSI bus operation.  If the drive is misbehaving, the SCSI
firmware might be coping, but the SCSI Manager might be fussier.

To verify this, disable or remove the SCSI.Manager and SCSIHD.Driver files
from the hard drive (in System:Drivers) and try booting again.  GS/OS will
display a warning message during boot, but will let you continue booting,
using the firmware.  (It doesn't allow access to any partitions except the
first.)  If this works, then the SCSI Manager doesn't like the drive for
some reason.

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand