When using Interbus, if the Interbus tophats do not show a solid green BA and RC light, you have a network problem. To view the status of the Interbus network, you will want to go to the Controller Status and look at word 4. The value in word 4 points to the last module it can communicate with (ie.. a value of 6 is pointing at the 6th module). The possibilities are one of the following:
1) the output driver on module 6 is bad
2) the cable is bad from module 6 to module 7
3) the 7th module or top hat is bad.