Communication between AB PLC's

Chris_M

Member
Join Date
May 2022
Location
PA
Posts
40
My plant has several CompactLogix 1769-L32 PLC's programmed with RSLogix 5000 V 20.05
as we look into expansions and upgrades would there be a communications issue if we ran newer PLC's?
The company has Studio 5000 V32.01
Would adding PLC's compatible with the newer software cause issues when using the Message tag between different generations of PLCs?
Thanks
 
That's a great question, and simple answer is "no, adding PLCs compatible with the newer software will not cause issues with communications".

The syntax and protocol and firmware support for ordinary MSG based Tag reads and writes are universally compatible among ControlLogix firmware revisions, from v2 in 1998 to v34 today.

The most common stumbling block that I see when folks are using those older 2nd-generation CompactLogix controllers is the CIP Path.

The older controllers emulated a ControlLogix in Slot 0, so you had to account for the virtual backplane and Slot 0 in the CIP Path configuration for the MSG instruction. Modern CompactLogix and 1756-L8x controllers have the Ethernet port physically and logically built into the controller, so the CIP Path omits that last segment.

If you are using Produced/Consumed Tags, there are a handful of details to be aware of, such as the automatic CONNECTION_STATUS element feature in a UDT, and how to exchange data with Safety controllers, since both of those were features not present in 1998. There's a whole detailed Programming Manual on that, 1756-PM011.
 

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