modbus not working on ML1400

[TimD]

Hi All,

I have modbus comms working to many devices using ML1400's and the NC01 adapter.

I have one flowmeter in particular from Toshiba that refuses to talk to my 1400, but talks to Modscan on my laptop just fine.

Of course, my port settings are set up OK on both PLC and Logix end. I'm reading an integer value from register 40001 just fine in Modscan, but when hooked up to PLC, reading nothing but time outs.

I've swapped A and B and changed all sorts of things in my MSG block and port settings to no avail.

I've never had this much trouble communicating to a device before. Toshiba tech recommends me buying a RedLion converter box of some type to help get the signal into the ML1400... I am not sure of that...

Anyone have any ideas?

Thanks!

 

[sfindley]

Check out this thread.

Pay particular attention to post #7....I fought with a 1400 for several weeks before I found the answer. Hope this is the one for you too!

 

[harryting]

Modscan is a master, right? Have you tried to run a modbus slave on your laptop and have the PLC read it?

I used this one before:

http://www.plcsimulator.org/

What's the exact modbus error code?

 

[TimD]

Error is simply "Message timed out in local processor"

I will try simulating a slave device now.

 

[TimD]

I tried the Modbus simulator, however, I only have a USB to RS485 adapter and the software seems to support DF1/232 serial so I'm not getting any results back. I can't see where to simulate a node address and the help says nothing. So, trying a "1" is no help.

My Modscan and USB adapter act as a Master and read data from the flowemeter just fine, however, the ML1400 refuses to read anything no matter what I try. It's frustrating.

 

[harryting]

Check out the link posted by sfindley above. The link I posted is to a modbus slave simulator.

post your file if you can.

 

[TimD]

Yes, I looked at the post, and my channel settings are correct (No Handshaking)

My file is a simple two line program, a timer (TON) that cycles every 4 seconds and triggers a MSG read.

The MSG block is set up like:
Channel: 0 (Internal)
Modbus Command: 03
Data Table Address: N7:1
Size in Elements: 1
Data: 16bit

Message Timeout: 2
MB Data Address: 1
Slave Node Address: 2
Modbus Address: 40001

..keep in mind I have been changing things to see what sticks like 16 or 32 bit and number of integers, etc... Yes, the slave node address is 2

And I've got VFDs on different ML1400 Processors talking modbus just fine...

 

[sfindley]

I had the exact same problem..check out the settings for your ML1400 and make sure you have "no handshake" like the description in the thread I posted