On 02/28/2011 08:56 AM, Moses McKnight wrote:
>> 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
>
> Sounds like standard ethernet frames.  I would imagine they would use
> standard frames because ethernet hardware is expecting that.
>
> http://en.wikipedia.org/wiki/Ethernet_frame
>
> Moses

Almost, except that standard Ethernet frames are typically of 
non-variable length, adjustable only by changing the MTU, and are 
"padded" to maintain the frame length being used.  The Sercos3 seemingly 
allows variable length frames.

Mark

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