Chris Elston

Allen Bradley Ethernet/IP Mapping Size Limit?

28 posts in this topic

On 8/23/2022 at 6:14 AM, BigTomek said:

Do you have any new news about this topic.Now I am in same situation.How do you solve this problem?

I have NOT gotten Large Forward Open to work with ANY Compact Logix. I was told that a Control Logix and 1756-EN2T(R) can do it, but I haven't a project that requires a Control Logix to confirm it. At this time, I agree with @pturmel above, I have not been able to get any Rockwell products to support this feature of Ethernet/IP.

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On 12/9/2020 at 5:56 AM, Mark Short said:

FWIW my experience with the Large Forward Open service and Allen Bradley devices is that the Logix range will only support a connection size of about 4000 bytes...

I had the same results, 4003 bytes.

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Edited by Mark-

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Yes, you can use ~4000 byte buffers with modern logix hardware and Class 3 messaging.  Nowhere will Logix allow more 500 bytes payload in a Class 1 traffic.  I/O connections and producer/consumer tags are Class 1 (payloads are delivered via UDP).  I have had success with large forward open I/O connections with Omron and Keyence products (max varies by product, but is typically 600 bytes or 1440 bytes).

Rockwell simply is not keeping up with the competition for a protocol they invented. ):

(BTW, Micro800 doesn't do Class 1 I/O connections at all.)

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