PF4 and Micro 1100 comms problem

[slcman 9]

Hi all, I got a strange problem. I have a project with 1 M1100 who communicate with 1 PV+ thru ethernet and 7 PF4 drive thru modbus DSI by using 1763-NC01 adapter. Don't worry, I do cascading comms, so DN or ER bit of previous msg is used as trigger for next msg (see picture). Everything work perfect unitl I start the drive, then I got timout error #37 on almost all drive. There is no difference in amount of data and logic in comm while the drive is stopped or running. I'm looking ER bit of MSG instruction, while all drive are stopped no ER bit are set and while drive running all ER are set. I found nothing in AB knowlegdebase on this kind of issue. Last point, I did similar project at least 7 times and I never got this trouble with the same comm logic in M1100. All previous project use the same drive but with an older firmware (5.10) and this project use firmware 6.01. New feature of firmware 6.01 have parameter 118, regarding comms Save / Ram (parameter is set to Save but I didn't write any paramter in logic). thanks for your help

[Ken Roach 194]

I'm going to guess that the problem isn't in your logic but rather in the serial wiring. RS-485 can be fairly noise-immune, but AC drives are notorious noise generators. Check to see if there's something different in the grounding of these drives or the MicroLogix as compared to your previous installations.