Modbus Communication Problem using AllenBradley Powerflex 4M and Micrologix 1100

HDB

Member
Join Date
Jun 2011
Location
Perth
Posts
3
Hi all,

I am looking to find out where my problem is regarding this situation. To my knowledge I have all the correct settings, but when I remove the Modbus Connection from my VSD, the VSD does not show a Comms Fault, even though i set it to 'fault if comms loss'
any ideas?

My PowerFlex Settings are:

Start Source =5 Comms Port
Speed Ref = 5 Comms Port
Comms Data Rate = 4 (19.2 K, and is matched with my program configuration)
Node Address = 1 (Unique address)
Comms Format = 0 RTU 8 N -1

I also checked Parameter D012 which correctly shows the value of 55 confirming that the Control Source is Via Modbus Comms.

With my really basic program running,
I have also interogated d015, but I get a value of : 0000 without any activity, so its very hard to diagnose at the moment.

A little stuck, and some advice would be appreciated.

Ps: Wiring to VSD is done exactly as RS485 Protocol in Appendix C of the 4M manual.
 
Yes I did. I understand that the new parameters dont take effect until a power cycle on the VSD is done. I confirmed did confirm that it does retain the new parameters.
 
What is the setting for U305, the Comm Loss Time ? The default is 5 seconds but it can be as large as 60.

I don't think the Comm Loss Timer starts running until the controller receives its first Command message, even if that message doesn't contain a Start command. Is your message logic running successfully ?

There's a very complete example of programming this Messaging in RA Knowledgebase 33774.
 
Thank you Ken for your assistance. I used the code to make sure that code-wise things were fine.

The problem was actually a weird one.
I had a Rockwell document (not sure how old - called: PowerFlex Class Modbus Errors) showing that wiring should be from pin 4 & 5 of my AIC (was using AIC) to pin 1 & 8 of my Modbus connector. But the Rockwell link that you sent me showed, from 4 & 5 to 4 & 5. Which made all the difference.

thanks for your help.
 
Hi HDB,

Are you not using the 1763-NC01 to connect from the Micrologix (via 8-pin mini Din)? I do find it makes life (a little) easier!

Regards,

Rob
 
HDB, the document you mention is showing pins 1 and 8 for orientation purposes only. It also shows the two pin adapter. It is breaking out pins 4 and 5 (though it is very difficult to see those numbers.) I don't know why it bothers to show the PLC connection numbers on the left since they would vary widely by PLC.

You referred to the full manual for that drive. You should have stayed following its drawings.
 
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