1756-ENBT between two ControlLogix PLCs

[gromit 4]

I need to setup two 1756-ENBT modules between two ControlLogix PLCs. The chassis are several hundred feet away from each other, and are connected via one or two ethernet switches. How does the transfer of data between the two chassis take place. One of the chassis also have a MVI56-MNET module installed, to talk to a separate foreign device, and it is going through one of the same switches located in the field.

[Ken Roach 194]

You can use the MSG instruction to send unscheduled messages containing tag data from one ControlLogix to the other, or you can use Produced/Consumed Tags, which automatically exchange data using the same mechanism as I/O racks on Ethernet. The best summary book for you to read is EtherNet/IP Modules in Logix 5000 Control Systems, which is available in PDF and hardcopy from Rockwell Automation. http://literature.rockwellautomation.com/i...um001_-en-p.pdf

[BobLfoot 302]

One thing not in Ken's great manual but worth considering is if you go the MSG route, use only reads and not writes. This is because reads are more efficient and IMHO leave less to wonder when trying to debug and chase thru code.

[gromit 4]

Thanks guys, I have downloaded the proposed manual and will review.

[Bill Linne 0]

And one thing that MSG reads will not allow you to do is "report by exception", or in other words, send the data only when it changes. I've found MSG Writes to be useful (in spite of their increased 'housekeeping' requirements) when you need to update the distant processor infrequently as the situation changes in the source processor. Edited 23 Oct 2007 by Bill Linne