Technical Q&As
DV 12 - SCSI Printer Prevents System Boot (1-July-95)
Q Our printer uses SCSI as one of its interfaces and operates normally with all
interfaces except SCSI. When the printer is connected to a Power Mac 7100 using
the SCSI interface, the computer won't boot. If we turn the printer off, the
Happy Mac shows up on the screen, and the Power Mac boots normally. How do we
troubleshoot this problem?
A The most likely causes are termination and bus-ID conflicts. If your device is
using the same bus ID as some other SCSI device on the chain, it can prevent
the boot sequence from preceding. This problem could also occur if your device
has a permanent hard-wired terminator and there is another terminator on the
bus.
There is one other possibility that relates to the Macintosh boot sequence.
When the Mac bootstrap sees a device, it tries to read block zero. If your
printer has a long warm-up period before it can fully respond to a read
request, it may be stalling the bootstrap. You can check this by booting the
Macintosh and waiting to see if the problem clears itself when the printer is
fully initialized.
The best way to troubleshoot the problem is to use a SCSI-bus analyzer, so you
can see the actual bootstrap sequence.
Technical Q&As
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