1. A control system comprising: a master station that includes a first memory and a first processing unit that executes a user program, the user program accessing a plurality of positions in the first memory by using different logical addresses; and a remote station that includes a second processing unit, a subunit to or from which one or more pieces of data is input or output, a first buffer for data transfer between the first memory and the subunit, and a second memory, the remote station being connected to the master station through a transmission path, wherein the master station stores in advance first assignment information that associates each of the positions in the first memory with the first buffer for each of the logical addresses, the first processing unit transmits, to the second processing unit, first designation information designating data that is among the one or more pieces of data and to which a logical address is assigned and second designation information designating an assignment rule, and after the first designation information and the second designation information are received, the second processing unit assigns data that is designated by the first designation information and to which the logical address is assigned to the first buffer in accordance with the assignment rule designated by the second designation information, writes an assignment result in second assignment information, and stores the second assignment information in the second memory.