hi,everyone..... I want to do the communication between eight controller(89v51rd2) using the modbus. in this one is master and others are slave. master should send the query, in response to this query slave should answer with its register status. in this logic master will send query to each slave at a fixed interval of time and will wait for slaves response. Means my communication is half duplex. so can anyone help me to write this programme/logic. Thanks