ControlLogix Max REAL Data Size for MSG

I'm trying to setup data exchange between two CLX's. Does anyone have any information on how big a single MSG instruction can send or receive? I mean, can a single MSG read 50 REAL data from the other CLX? Thanks in advance for any help.

I'm not aware of a limit but I suppose there must be one. From past experience I'm sure you'll have no problems at all exchanging 50 REAL's.

There really isn't a practical limit. If you request more data than can be handled in a single message packet, the MSG instruction will transparently read everything you want via multiple packets.

You haven't stated which network you are using.

For EtherNet, a single "packet" can deliver approximately 500 bytes of data.

A REAL is 32 bits = 4 bytes, so a MSG of 125 REALs will be handled in one "packet".

As already stated, multiple packets will be utilised to transfer larger data-sets.

I'll post back when and if I discover any differences if you are using ControlNet

rdrast said:

There really isn't a practical limit. If you request more data than can be handled in a single message packet, the MSG instruction will transparently read everything you want via multiple packets.

Click to expand...

There is a limit... A single tag in Logix5000 controllers cannot be more than 2 MB in size... so for REALs, that's an array over 524,000 elements !!

Thanks for all the responses. Sorry, I didn't specify the network, we're using Ethernet. Our project involves around 10 PLC's and the customer specifically requested that no Produced/Consumed tags be used. So we're forced to MSG all required data between PLC's. My concern was to limit as much as possible the number of active MSG's for bandwidth optimization (MSG qeueing already implemented). So if 1 MSG can handle around 125 REAL's and only use one packet then that's great. Thanks again to everyone who responded. Will post back any observation after implementing this.