Rick Fogel <[log in to unmask]> wrote:
> What is the differance between active and passive terminators. Also, what
> does passthrough mean? Some come with led lites. What are these for? I need
> to terminate my scanner which has both a 25 pin plug and a 50 pin cetronics
> plug. I have the scanner plugged into the scsi card with the 50 pin which
> leaves me with the 25 pin plug to terminate or should i get an adapter to
> change the 25 to 50 pins. This is the only device i will use extrenally but
> have a cd-r hooked internally.The card is a Advansys 940 Ultra.

Passive terminators just have a simple resistor network between power (TERMPWR)
and ground. Active terminators use a constant current source to try and make a
more consistent termination current on the signals. There are also Force Perfect
terminators which use even more sophisticated method to sense the line
characteristics and match them exactly.

The LED lits simple indicate that there is volatge on the TERMPWR signal,
nothing more.

Passthrough simple means that there are two connectors on the termninator,
designed for SCSI devices that have only one connector. The path from the
terminator to the device must be as short as possible (or the effect of the
terminator is useless).

To determine how to terminate your scanner, you need to see what the manual
says. If it has built-in termination, you should enable it. If not, you need to
determine if the second connector is pass through, if so, you can put a
terminator on it (I recommend an active terminator).

If you have both internal and external devices, then the ends of both busses
needs to be terminated (scanner and CDR), and the controller should NOT be
terminated.


--
Russ Poffenberger               Engineering Specialist
Schlumberger Technologies ATE   DOMAIN: [log in to unmask]
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