ControlLogix Message Error 16#001b - Bridging failure, Response packet too lage

[Ken Roach]

Another thought, though I'm sure you are very familiar with Modbus by now:

Conventional Modbus "register addressing" begins with Address 1, which is located at Offset 00.

Therefore when you're looking at raw Modbus commands, the byte that holds the Offset value is always 1 less than the "Address" you intend to read.

Nearly every time I do Modbus data transfer, I have to guess, test, and change my assumption about the actual "first register".

I don't know the XPort device, and I don't know your application, but the message you are sending looks like it will read starting at the second register (offset 01) instead of the first register (offset 00). I could be off base, as well, because you mentioned this is a configuration command rather than a real Modbus Function call.

 

[Ken Roach]

ACD file and screenshot included / attached below:

 

[mihiri]

Hello Ken,

Thank you so much for the reply. I attempted to send the settings into the Xport using a Array of SINT[5] and I can observe now that the PLC is sending the correct data I want to the Xport module.

03 01 00 40 00

Which is Modbus function 03 at starting at register 1 for 64 registers. It gives a Resources unavailable error. But we were able to fix the major issue of Oversize byte issue we had previously. Fantastic, now I have to investigate why I am receiving the Resources unavailable error 0x02, which might be something to do with the Modbus Slave from the our application relay.

Once again thank you very much for your response.

Cheers,
Regards,
Mihiri

 

[mihiri]

I have attached the Application Relay settings..this specifies all the Modbus settings on the MPA (Motor Protection Relay). Screen shots shows the Modbus settings and the list of Registers used. As far as I understand I have mapped all the other relevant correctly as how it sits on the Modbus Slave End..

Out of interest I have attached is Xport Firmware V1.13 Manual Config settings and curret existing config.bin file on the Xport manual.

 

[mihiri]

Hello Ken,

I was able to fix the Resources Unavailable Error that I was receiving from the Xport. This was due to the Logic level from the Xport wasn't getting pulled up correctly to the Modbus side ( A slight circuitry design error on the application side). After this was completed I was able to successfully set the Modbus settings (0x03, start address 0x0001 and holding register number 64).

Thus for me to read the values stored the modbus registers I created a new ControlLogix5561 project with the Xport module added as a generic EtherNet/IP device and specified the connection parameters as follows;

please see the attached figure;

Interestingly if i set the Input parameter 101 to size 1 I can connect to the module, but if I set to that to be 2 there is a timeout error. I don't get what is this these connection parameter settings are on ControlLogix5561.

Since I need to read the data available on the 64 holding registers as I have specified in the config file of the Xport shouldn't I set this to size 64 ?

Would you be able to guide me through how I can construct a ladder logic code to read data from the Modbus registers into the RSLogix 5000.

A reply is much appreciated,
Regards,