MSG reading from ML1400 - Whats the Max number of elements?

[TheWaterboy]

I'm trying to read a table of 100 floats over ethernet from a ML1400 to an L61 CLX.

I find I can only read 58 elements at a time before the MSG throws a [16#003 Configuration data size too short] error message.

These Floats = 58 x 2 or 116 words of data.

The receiving array in the L61 controller is 250 elements long.

Where are the limitations of MSG'ing between an ML1400 and an L61 spelled out?
Is this a real limitation or am I perhaps doing something else wrong?

 

[Ken Roach]

It's an SLC/MicroLogix operating system (or maybe protocol) limit: you can exchange 117 Integers or 58 Floats or Longs with a MicroLogix 1100/1400 or SLC-5/05 with a single message request.

The only workaround is to break the messages up into smaller blocks.

 

[TheWaterboy]

OK considering the source I can accept that answer without question. But where is this written?
How about strings?

Does serial do better/different?

Does the 5380 have any such limitations? where are those spelled out?

I'm testing telemetry this week and these are my test files. The discussion of Ethernet vs Serial over VHF will follow.

 

[Ken Roach]

I can't be exhaustive or authoritative, but I know you're serious about your telemetry so I'll toss in what I know.

The 58 Float limit came from the Knowledgebase, article 525413 (TechConnect Required).

I suspect the limit is the same for serial and for Ethernet, because Ethernet can generally carry much longer data payloads. I think it's an operating system limit. Or, there might be a small difference because of the addressing overhead; I found an old post from myself claiming you could read 122 words from an SLC over DF1.

Strings, I'm not sure.

If I was searching for source material I'd probably break out the DF1 protocol manual, but it hasn't been updated since long before the MicroLogix 1100/1400 operating systems were developed.

ControlLogix message block lengths are different. My recollection is that the maximum length block is 500 bytes, minus some header data, so the usual data size length limit is 480 bytes.

Some ControlLogix devices (v20 and later) support a "large data" mode that allows more data between Logix devices as part of a single transaction. 3980 bytes for a Large Data transaction shows up in a quick glance at the 1756-RM003 reference manual.