I don’t believe that HT Basic has native support for Modbus. You can download Modscan if you wish to communicate with a Modbus device (serial/TCPIP). You can also download Modsim if you want to simulate a Modbus device. Both s/w packages are usable on a free trial basis and are very inexpensive to purchase outright. You can also use Python and the pymodbus protocol stack vs. HT Basic.