George - this is not directly related to the thread, but it is about the ROK...and from your posts I take it you've got experience. I am configuring one right now, and at the point of "System Checkout" it is telling me the "serial connection between arbiter and controller (for both 1 and 2)" have a problem. I've checked wiring pretty thoroughly (good terminations, proper terminals, continuity). CTR2 on the arbiter has Tx and Rx blinking as are the corresponding Tx/Rx on Controller 2. CTR1 on the arbiter (and corresponding on Controller 1) are not lit up at all. When I remove the terminal block from the arbiter for CTR2, Tx continues to blink. The controllers are S2's. In PAC Manager, both their Serial Port 2 (the ones used in Redundancy) show the identical settings. Those settings FYI are "Control Function = None, Logging = Disabled, Mode = 2-Wire RS485, Termination, Bias. I did not set these, they were what showed up.