RS-485 Serial communication problem with arduino
In modbus there are two pins which are as DE and RE which you need to set and reset while transmitting the data. Also you can check Modbus this library it has some examples which could be useful to you also in arduino Uno don't use software serial for transmitting the data use the hardware serial only I will suggest implement your code on arduino Mega if you have any and then port the code for Uno. Just go through the library you will find some helpful examples and it will solve your issue