info abt address n data buses in plcs?

hi
i jst wanted to know if there are address n data buses in controllers jst like the ones in microprocessors?

n secondly what bit is controllogix n plcs and slcs-jst give a few examples

also i want to knw how is a tag related to the i/o module?
i mean how does the controller know that this tag value is to come from that particular bit of that module.

thanx for any help in advance

1) Yes, Address and Data Buss.
2) ???
3) Modules are mapped to specified locations in memory.