Emax

Termination should be at the end of the cable.
It prevents "reflection" of signals through the cable. Even cable length
that is "unconnected" can reflect signal.
Turning on termination when the drive / connection is not at the end of the
cable is not the "best practice" way of terminating it and may result in
intermittent issues.

Depending on how you have SCSI in Emax hooked up, there is the possibility
of two termination setups.

On rev 3 boards / factory modified boards where there are two headers (one
50 pin for internal and one for external DB25 right off the logic board),
then the 5380 could be considered to be basically in the middle of the SCSI
bus chain.

In that scenario.... as a single chain
INTERNAL DRIVE with TERMPWR on 50pin connector ------ 5380 SCSI controller
------- external port from logic---- external drive---- external drive ---
terminator

However, if you only have the 50 pin connector, then I believe it should be
like this if using internal and external drives:
5380 ----- internal drive (no term) ------ external connector ------
external drive ----- terminator

when there is no external drive I would put the terminator right on the
external connector.

Keep in mind that (IIRC):
* each connection on the scsi bus = loss of length of 6 inches of cable from
"max length" the chain is allowed to be.
* cables should always be kept to the minimum length possible to prevent
issue, but connectors should be at even spacing. The spacing is typically
determined by the length of the cable and different mfrs do not always
adhere to the spec to minimize reflection down the cable length.
*you may need an active terminator or passive depending on the bus.

YMMV, but that is what I know from my experience with SCSI (generally
speaking- from "on the job" using SAN storage and JBOD storage, and internal
HD, Tape, and CDROM - all SCSI).


Regards,
Ted


On Tue, Jan 12, 2010 at 9:23 AM, thenewyorkcowboy <
thenewyorkcowboy@...> wrote:

>
>
> I am still having intermittent failures with my SCSI setup and have a
> general question about termination. At this point I am convinced that the
> ZILOG chip just was not advanced enough in it's day to be compatible with
> devices that SAY they are backwards compatible. The data sheet says the chip
> does 3mb where we all know SCSI-1 should have been 5mb. If a major standard
> like that was compromised, I can't imagine what other shortcuts they took.
>
> If the EMAX II models that originally were HD models had an internal drive
> mounted by the factory AND still had the external SCSI port, how exactly did
> they get around proper termination? Did they come with a 25 pin terminator
> that acted like a cap to the port that you had to keep track of as an
> accessory?
>
> I am considering installing a mini toggle SPST switch that sticks through
> one of the slots in the back to turn on TRMPWR on the ACARD adapter to
> terminate the ZIP drive I am trying to install for when I want to connect an
> external device as well.
>
> Any help or suggestions?
>
> 
>


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