Controllogix + 1769-SM2 + Altivar 312 Modbus Communication

[renan.musardo]

Hello everyone.

I'm trying to communicate a Controllogix L36ERM with a 1769-SM2 Modbus module to a Schneider-electric Altivar 312 Modbus motor inverter, however communications doesn't seen to work.

Here's what I already have:

Altivar 312 Configs:
Addresses: 31...36 (6 inverters, however, I'm trying to test only one until finding out the problem)
tFo: 8N1
tBr: 19K2
SR1: MdB
Inverter is signaling "nST" (Something like "waiting for input")

1769-SM2 Configs
5x / Controller (on DipSwitches)

At data parameters, I have:

CH1:
W#3 = 5 (Modbus Master)
W#4 = 31 (Node adress)
W#5 = 32 (Node adress)
W#9 = 1 (Baud rate = 19k2 bps)
W#10 = 0 (Format = 8N1)
W#11 = 50 (50 ms RX delay)
W#12 = 50 (50 ms TX delay)
W#13 = 5 (5 sec MSG timeout)

CH2/CH3: Same configs as above, except for node adresses.

I was trying to read the Communication words: W#3201/ W#3202, but I've received nothing (zero...)

The only thing I didn't checked was the cable. The SM2 module was like this:

LED Module: Fixed Green
LED CH1: Off
LED CH2: Off
LED CH3: Off


The inverters are already installed in the client, four hours away from me, so I need to check the software and parameters first, before trying to check cabling.
The PLC is with me, so I can change parameters, however, I can't test with the inverter...


I appreciate any help and thanks in advance

 

[damica1]

I know nothing about the "ControlLogix", But I have communicated with Altivar drives with modbus using the Micro820.

All of my addressing had the +1 offset - so if your wanting to read address 8501 you would request a read from address 8502. The function code should be 03 this is the read command.

You may also want to read this:

https://www.schneider-electric.us/en/faqs/FA243246/

 

[renan.musardo]

The function code should be 03 this is the read command.

Thanks for your reply! But what's this function code that you are talking about? Where do I see this code? In the inverter or in the PLC?

 

[nhatsen]

I'm trying to communicate a Controllogix L36ERM...

L36ERM is CompactLogix.

... with a 1769-SM2 Modbus module to a Schneider-electric Altivar 312 Modbus motor inverter, however communications doesn't seen to work...

... The only thing I didn't checked was the cable. The SM2 module was like this:

LED Module: Fixed Green
LED CH1: Off
LED CH2: Off
LED CH3: Off

Did you read the SM2 manual? Aside other helpful information, you'll find the in the troubleshooting section an explanation about the leds. If the channels are configured for Modbus Master and CH1-CH3 are off, check the wires.

 

[renan.musardo]

Thanks for the reply.

In the manual, pages 153-155 (Troubleshooting), I've found the LED indicator statuses.
Since they're off, it means that the problem is probably the cable.

Just for information purposes, I'll paste here for future references.

(Attached file)

Thanks again.

 

[danw]

No experience with either, just generic Modbus observations:

Your PLC is (supposed to be) the master. Masters do not have node addresses, only slaves have node addresses (31-36).

The rule for serial Modbus is one master only, so if the PLC is a Modbus master, it can't be a slave, too, because there would have to be 2nd master addressing the PLC as a slave.

Modbus is a master/slave protocol and slaves are silent unless spoken to. There is no such Modbus slave function as "signaling" a state. Slaves wait silently until they decode a message addresses to their node address and then reply. Hopefully nST is just 'waiting', not broadcasting a 'ready' signal.

> But what's this function code that you are talking about?
The master has to compile a query message to send to the slave.
That message has to include the slave's node address, the function code that the slave is to execute (FC03 is "Read Holding Register(s)), and the range of contiguous registers in the slave that the function code is dealing with.
So, somewhere in a Master is a something like a function block that one configures with those items, and probably an 'enable' function as well, where enable executes a message transaction.
Upon receipt of the data, the Master has to do something with the data, move it somewhere, because the data will be overwritten during the transaction.

The Modbus slave is relatively passive, it waits until it gets a message, then replies with the data in its registers or writes data to those registers (different function code).

Modbus is a project, there's nothing plug-n-play about it.

 

[renan.musardo]

Hello everyone.
A quick update.

I am still working on this and found out that the REAL problem is the SM2 module...

 

[antoniomrc]

Hi, did you find the problem?