How to terminate your devices
If you are familiar with 10Base2 BNC cables
in networking, you will remember that you need to put terminators on both ends
to dampen out the reflected signals. Well, terminators in SCSI do the same
thing.
Note that the SCSI cards I mentioned automatically
terminates one side of the bus. The bus is basically the SCSI cable. The other
side is terminated by the last device on the bus (usually by a jumper if
supported) or by an external terminator. All cables need to be terminated. This
means you need termination at the end of the 68 pin cable and at the end of the
50 pin cable.
Now if your using an external scanner on an external
connector, then terminate the scanner and terminate the internal devices on the
same bus. The SCSI Adapter must not be terminated when using external devices.
Here's how it works.
SCSI CARD (auto termination) -------------- drive -------
drive ------ drive ------ drive------ (last drive terminated or external
terminator)
or with an external device
---- last external device--- (terminated)
----------SCSI CARD (NOT terminated) -------- drive (internals) --------last
Device (terminated)
In this case, you may have to disable termination on your SCSI Card (by entering
SCSI BIOS, see below). Note that the Adaptec series automatically detects if the
card should terminate or not by default.
The SCSI cards have a BIOS which controls your cards settings.
On bootup, you will see a message that looks similar to this (Press CTRL-A to
enter setup utility). Just press CTRL-A at this time. Note: that CTRL-A is for
Adaptec controllers. Entering the BIOS on the Tekram controllers may be
different.
Next page: The BIOS & External Terminators
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