One FB can adress more than one DB (when you create a FB check for "Multiple Instance Capabilities"). For example,each motor has assigned a DB according with its characteristics but an FB can process many motors, differences are given by the associated DBs. One specific adress in the same DBs (base=point of start DB + deplacement= offset to base)point to the same parameter, with value determined by motor. Ex: DB2 and DB3 are 2 DBs assigned to motor 2 and motor 3, at adressses DB2.DW36 and DB3.DW36 you can find the actual speed of motor as parameter, but the values can be different (DB2.DW36=1200rpm, DB3.DW36=1500rpm).In the S7 program, in FB, you can select the DB you need witn instruction OPN DIx, in the lines below you use the instance DBx as supplying block for FB variables.