Variable Frequency Drives (VFDs) are electronic power controllers that allow for accurate control of the speed of alternating current (AC) induction motors that used in many kinds of machines including fans, pumps and compressors. These motors are used in most heating, ventilation and air-conditioning (HVAC) systems and account for a significant percentage of the total HVAC energy consumption. More efficient operation of these motors using VFDs can result in significant energy savings. Besides, the communication between VFDs and PLC for Supervisory Control And Data Acquisition (SCADA) is also important. Modbus protocol has many kinds as RS485, RTU, Profinet,...In this paper we will present the communication between a PLC Siemens S7-1200 and an ATV310 Drive (Schneider) via Modbus RTU protocol which is supported.