I have a similar problem as Monty K below whereby I also have a master & 9 slave T100MD's all connected together via their RS485 ports, though in my case each of them are connected to an ethernet network via individual nPort express RS485 to ethernet converter server units.
The problem I have is that the system will function happily for over a day without incident and then for no apparent reason all the slaves will lock up!
I've incorporated a MaRST facility into each slave where if I press two buttons simultaneously the PLC will reset (which normally works OK), but when I get these lockup conditions occuring the MaRST doesn't work. Only a complete power down/power up cycle works, which is far from ???ideal!
Do you have any idea as to what maybe causing these simultaneous lockups occuring, and why the MaRST facility doesn't work when it happens? ?