Sercos 3 was one example of the use of ethernet for real time control.

Another example is ethernet i/p. Again it uses standard ethernet technology and 
allows the use of switches between the host and slave. It all comes down to 
timing. AB claims they do +/- 100 uS without modified hardware. With IEEE 1588 
compliant hardware they can get it down much lower.  It all comes down to the 
application and what is required.

Refer to ODVA's CIP Motion and CIP Sync for more information. 

I use AB PLC's and Bosch Rexroth drives   using ethernet I/P communication on a 
daily basis without 1588 hardware and have found it to offer exceptional 
performance. 

My comments were relating to someone indicating that ethernet could not be used 
in a real-time application.

Thanks
Jp

Sent on the TELUS Mobility network with BlackBerry

-----Original Message-----
From: Mark Wendt <mark.we...@nrl.navy.mil>
Date: Mon, 28 Feb 2011 08:37:19 
To: Enhanced Machine Controller (EMC)<emc-users@lists.sourceforge.net>
Reply-To: mark.we...@nrl.navy.mil, "Enhanced Machine Controller \(EMC\)"
        <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Guidance on usb comp

On 02/28/2011 08:19 AM, Dave wrote:
> Siemens DriveCliq works the same way.   Everything is point to point.
> No external hubs or switches.
> I think the controller I was using recently had 6 or 8 Ethernet jacks.
> The drive module had 3, one for the connection to the controller and two
> for encoder connections.
> I think the line module (Ac to DC smart power supply) had 3 Ethernet
> jacks.     Hooking everything up was very quick.
>
> Dave

Looking again at the Sercos3 implementation, each "host" requires at 
least a two-port network interace.  That's how they implement either the 
"Line", "Ring" or other network topology.  Each "host" has to process 
the data and then pass it on to the next host in a host 2+n topology.

The "Ring" topology looks to be the most efficient, since two channels 
are being used to move the data around the circuit, and the second 
channel offers a bit of redundancy of the primary channel goes down.

For environments that have multiple machines, this could be an issue 
with multiple, long network cables going from the master controller to 
the slave boxes.  With that in mind though, it's kind of hard to imagine 
multiple instances of EMC2 running on one controller PC controlling 
different machines.  For a single control PC sending data to a single 
control box, this shouldn't really be an issue.

Interesting also how the protocol utilizes multiple length packets (or 
as they call them, Telegrams), anywhere from 84 bytes to 1538 bytes in 
length.

Mark

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