Re: More VAX help needed
From: Verell Boaen VMScluster Comm. Architect (Verell.Boaen_at_hp.com)
Date: 05/05/05
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Date: Thu, 05 May 2005 17:36:24 GMT
Hello Bill,
"Bill Gunshannon" <bill@cs.uofs.edu> wrote in message
news:3dpbekF6rifjsU1@individual.net...
> got the idea that I could
> connect my storageworks cabinet to a sikngle 6640 without a star
> coupler.
>... the local VMS guru and he said it won't
> work without a star coupler.
That's correct,
You must have a star coupler for a several reasons:
- A star coupler provides attenuation (18db min/27db max 10-100Mhz ) of the
transmit signal needed to bring it's amplitude down within the range of the
receiver.
- It permits all nodes sending on a path see each others signals on that CI
path. This is necessary to ensure:
. that a node's receive circuitry is available to receive an ACK
(acknowledgment frame) immediately after a packet is transmitted.
. That a node is not transmitting when another node is sending packets, thus
ensuring that the node's transmitter is available to send an ACK immediately
upon receiving the packet.
. Loop-back works ie: a node can test the path by sending packets to
itself. VMS driver & CI adapter firmware self-test must verify that an
adapter can at least successfully send packets to itself on at least one CI
path before the adapter is brought online. BTW, The CIPCA requires that
loopback work on both paths to pass self-test.
ROLLING YOUR OWN:
If you can't come up with a star coupler, you can make one out of a resistor
network. A simple T network with each transmit cable attached to the center
of the T thru a resistor, a resistor to ground for the bottom leg of the T,
and a resistor from the center of the T to each input cable. All cable
grounds are tied together at the bottom of the T. The input and output
impedence must be 50 ohms.
The resistor values must provide the attenuation previously mentioned.
Helpfully,
Verell Boaen
VMScluster Communications Architect
- Next message: Hoff Hoffman: "Re: A C programming question"
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- In reply to: Bill Gunshannon: "More VAX help needed"
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