I have one master and 20 slave uC (8052). A master will always send and receive the information from the slave. The distance between the boards may be around 200 meters. I want to use 8052's serial interface. I have an idea to connect all slave's Rx to the master Tx and connect all slave's Tx to master's Rx. Master will send commands via rs232 and all slave will listen to that. Only one (addressed) slave will do the job what master has asked for.

To avoid colosion, i may use a 3rd wire (enable) which will be open drain so who ever wants to snd any info it will pull this wire down and will keep it down until it finishes the communication. Meanwhile other uC those wants to send the info will detect that enable signal is high or not. If it is high then one will pull the signal down and will transmit the data. And if not then it will wait until that signal goes high.

Any suggestion???

Rauf