The figure above shows the network wire RS-485 2. With this configuration, apply the half-duplex communication, two-way alternate. Master for he who initiate the communication, will be the first to connect the transmitter to its network, while the slave will connect the receivers.
Each slave will have the ID / unique address. Slave to the destination ID will then be mengaktidkan its transmitter when it will mereply permaintaan from the master. While the master will enable the receivers. Another slave who can only "listen"
In the system 4 wire, Master Transmitter connected to all slave receivers, while the receiver is connected to all the slave transmitter. In this system, the master transmitter can always be online to the network, because with four wire system, the communication can be run full-duplex, 2-way full. While the slave transmitters will only connect when there is a request from the master. The disadvantage of this system is the cable required two times more. Therefore, the network system with a distance which is much cheaper when using a 2 wire system.
As has been explained that the RS-485 specification does not address the communication protocols, therefore it can use any protocol, eg Modbus, etc.. In following posts we will make samples / simulation for RS-485 temperature sensor readings SHT11.
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