Programmable Logic Controller (PLC) is the most famous controller in industry. Because the process in industry is getting more and more complex than before, the USAge of more than one PLC is needed and the communication between them have to be existed. This paper describes about the study of communicating two Schneider TSX Micro 37-21 PLCs in order to control the miniature of beverage production. The usual (and expensive) way to communicate them is using converter module TSX P ACC 01. Less expensive way uses original converter cable TSX PCX 1031 that connect to the ports of PLCs (TER and AUX port) which will be explained here. PL7 Pro V 4.0 software is used to program the PLCs. The communication cannot be established due to some improper addressing. The exploration is continued to the serial communication. It is found that the system uses RS 485
