::This is a question about the 1540/1542 setup control for enabling termination.
::I've been trying to run Solaris 2.4 EA2 on a 486DX2/66.
::I have three internal SCSI devices and one external one (the external
::device is an 8mm tape drive).
::If I use the built-in setup interface to
::disable termination, which I should do since I have devices on both ends
::of the board, bootup hangs. If I enable termination, it boots up. Is this
::a hardware problem with my particular board?
::In either case, the "verify disk" operation works all the way through on a disk.
::Once the system boots up, with termination enabled, I can basically access all
:::the devices, including the 8mm tape, but I frequently get disk errors and
::tape errors, suggesting a termination problem.
::Thank you very much for your time and knowledge.
::--Leonard E. Sitongia HAO Sun Unix System Manager
::High Altitude Observatory P.O. Box 3000 Boulder CO 80307 USA
If you have internal SCSI devices *AND* an external SCSI device, the
termination on the controller should be disabled.
The last internal SCSI device in the chain should be terminated... usually
through termination resistors on the device itself. Other internal
SCSI devices should NOT be terminated.
The external SCSI device will generally have two SCSI ports to allow the
chaining of additional devices. You either open up your external device
and install termination resistors as appropriate, or you plug in a
termination block to the second SCSI port.
One common mistake is for people to plug in termination blocks without
providing termination power to the SCSI bus. The result is that the
termination block hurts more then it helps. You need to set ONE of
the SCSI devices up to provide termination power (usually a jumper).
It is generally a good idea to have whoever supplies termination power
be as close to the termination block as possible. (Frankly, the
termination blocks ought to have capacitors on the termination power,
but most of them are made as cheaply as possible).
Many people recommend having the external device supply the termination
power. Even more people recommend that you NOT use a termination block
and instead install termination resistors in the last external device
in the chain. The reason for this is that many SCSI devices leave out
a critical diode that prevents a powered down device from shorting out
* The last internal device and last external device is terminated.
i.e. the two ends of the bus must be terminated. Devices in the
middle of the bus are generally not terminated.
* If there are no external devices you can avoid the use of a
termination block by enabling termination on your controller,
which is usually a feature of the controller.
* If there are no internal devices but there are external devices,
you normally enable termination on the controller for the
* watch out if you use termination blocks: some device (or the
controller) must provide termination *power* to power the
termination block. If nobody is providing termination power,
the termination block may make matters even worse.
1005 Apollo Way ham: KC6LVW (no mail drop)
Incline Village, NV. 89451 Obvious Implementations Corporation
USA Sandel-Avery Engineering
[always include a portion of the original email in any response!]