Micrologix Modbus RTU RS-485 to Lantronix xPress DR+

[cholguin]

I have been trying to communicate to an Allen Bradley PLC a Micrologix 1100, using the RS-485 port configured as Modbus RTU Slave and getting this read by a Lantronix xPress DR+ so i can get the data to an HMI. The thing is that there is not much information on how to get the PLC fully configured for Modbus RTU Slave, or how to connect it to a RS-485 network (physically). I got the NC01 RS-485 cable connector from Allen Bradley and i connect it to the Lantronix as a two wire RS-485 connection, but got nothing, i even tried putting termination resistors (122 ohms) on both ends, but i don't know if i am doing it right, since Allen Bradley does not use TX+ or TX- it uses A or B, so anyway i tried every combination with the A and B and nothing.

In the software i configured in channel configuration channel 0 for Modbus RTU Slave and double checked the communication settings to match the Lantronix in speed and all that stuff, i also configured the data table, but nothing. I am verifying with ModSCAN32 and i see the Lantronix lighting, polling the PLC but i get no response from it. Please help!

 

[danw]

I can't attach the file because this forum's file size limitation is only 300Kb (file is about 900Kb).

The .doc file is titled

MicroLogix 1100 Communications via Modbus to PowerFlex.

By comparing the example and making appropriate substitutions, it might help.

Try downloading it from here:
http://www.taginfo.com.br/publico/R...00 communications via ModBus to PowerFlex.doc

 

[diat150]

id try and use a modbus polling software to poll it directly before trying the lantronix. modbus poll is a good one that has a trial.

 

[bernie_carlton]

Be sure that 'Protocol Control' - 'Control Line' is set to 'No Handshaking (485 Network)'

Make sure you don't have duplicate node addresses.

Just curious on what the 1100's Ethernet port is being used for that you have to do a conversion on Port 0?

 

[danw]

I've used Modscan32 to communicate with that model Lantronix. Modscan32 is more than capable of doing so.

This is likely a configuration issue.

 

[diat150]

here is how I configure my lantronix for modbus tcp.

 

[danw]

I'm confused about channel zero and wonder if it could be confused with broadcast mode.

Modbus broadcast mode is unidirectional, master to slave, with no slave response. Quote and image from Modbus Serial Line spec:

Avoid Broadcast mode is you want a response from the slave.

 

[diat150]

I think he meant channel 0 on the micrologix.

 

[diat150]

also, since the micrologix is a 2 wire device you mst jump out the terminals on the lantronix to make it 2 wire.

see this drawing. you may need to swap A and B, but this should be correct.

 

[ASK73]

here is how I configure my lantronix for modbus tcp.

HI...COming back to this post after a long time..I am trying to use the Lantronix module as well. This time with Quantum and tank gauge on the serial modbus connected to the lantronix. My issue is the tank is read correctly however every reading is followed by a reading of 512. Cannot understand what this 512 is ? the tank reading fluctuated between the actual reading and 512.
Pls help.,