text: <s>[INST] CIP Motion and PF755 Summary: How many here have encountered problems with CIP Motion and PF755I've a persistant, sporadic, irritating problem with two PF755 drives running under CIP motion. Tech Support is working the problem but have not yet found a conclusive problem. I've already contacted Vong and dwalserams about their problem posted here: http://forums.rockwellautomation.com/posts/8242c929e2 I am VERY interested in talking with anyone else who encounters problems with PF755 drives running under CIP Motion. Please feel free to respond here, or call if you wish. Sincerely, TJ McDermott Systems Interface 425-750-1629 (Pacific Time Zone) [/INST] Update: Rockwell sent a specialist to collect data on this problem. Luckily, the anomaly manifested while he was on site. Testing required a special, temporary firmware be installed in the two drives. This firmware provided access to additional parameters, one of which was the number of communication buffers in use in the drive. This buffer count is supposed to be zero, occasionally rising as low priority communication is deferred until the drive can handle them. We discovered that the buffer count will sometimes not go back to zero. Hitting the drive with web page accesses can really spike the count, but it eventually drops back down. Some sort of message from the network gets stuck in the buffer and doesn't get out. The count increases, until it gets close to 50. Upon reaching 50, the drive stops communicating via Linx. Cycling power to the drive resets the buffer count. So, we now know WHAT is happening, but not WHY. Regardless, the PF755 in CIP motion has a firmware problem that must be fixed; some message is getting stuck in the buffer and prevents anything that went in previous to it from getting back out of the buffer. Or, the buffer index is being messed up. Whatever, the drive doesn't handle all messages properly. The brute-force fix we're going to implement in the mean time is to add an additional 1756-EN2TR module to communicate directly to the two drives in this system. I know there are other PF755 CIP motion problems; it does feel like the 755 is a bit fragile compared to the Kinetix 6500 in CIP motion. Has anyone else had problems with PF755 in CIP motion? Any problem at all? \\n </s>