我对Modbus通信有点陌生，我很难搞清楚在“自由Modbus”的主人这一边使用什么功能

I'm a bit new to Modbus communications and I've started reading about the "Free Modbus" library. Now, I understood how to use it to implement the slave side of the Modbus communications, but I just can't seem to find how to use the library on the master's side. For example, what function show I call on the master's side to read discrete input number 3 of slave 19 (for instance)?I'm a bit new to Modbus communications and I've