Ken Roach already answered this question for MicroLogix 1200, I'm trying to find the same answer for MicroLogix 1000. DF1 half-duplex communication gets dropped with MicroLogix 1000 slaves. I monitored the data, and found the slaves stop sending ACK, and the master stops sending ENQ. Slaves still send valid responses, but these responses are ignored by master because the ACK is not present. Power cycle solves the problem, but that's a hassle to drive out to remote sites. Power cycle to master sometimes solves the problem, but not always. Messages are initiated by the master, not by the slaves. Rockwell support said the only solution is to cycle power. Ken's approach was to monitor CS0:17, if it changes issue an ACL command. See previous topic: http://forums.mrplc.com/index.php?showtopic=22686 Thank you!