There are various type of data bus in aviation, the two most common in the '90 were ARINC 429 for civil aviation and Mil 1553 for military applications. They are not very different one for the other, the Mil is a little more complex.

My question is: why use two different data bus? The physical cable is the same (as far as I know, you can correct me if I am wrong) but the protocol is different. I think that what a data bus must do is the same in civil and military avionics, am I wrong?