i have a plc Modicon M340 , HMI hmigxu3512x and VSD Altivar 71, and i only allowed to use serial MODBUS port in plc, now the VSD is a slave and is controlled with plc as a master how can i add the HMI to this configuration?? i know that this model of HMI can be slave but then how it will give orders to PLC to start stop etc.. and if PLC is slave how it will control the VSD??
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