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Home » Q&A » Advantages and disadvantages of RS485
Advantages and disadvantages of RS485
Published: 2012.02.19

RS485 adopts differential signal negative logic. +0.2 V - +6 V is indicated as ‘0’ and -6 V - -0.2 V is indicated as ‘1’. There are two-wire and four-wire connection modes. In CAMABIO system, two-wire is used. This connection is of bus topology structure, in which a maximum 256 nodes can be connected to the same bus. CAMABIO product's RS485 support maximum 128 nodes. In most circumstances, when connecting RS485 communication links, only a twisted pair is used to connect the ‘A’ and ‘B’ terminals of each interface. In theory, the maximum communication distance of RS485 can extend up to 1,200 meters.

The main advantages of RS485 are:

Logic ‘0’ and ‘1’ are indicated by the voltage differences between the two wires +0.2-6 V and -0.2-6 V respectively. The interface signal level is lower than that of RS-232-C, so the interface circuit chip is not easily damaged. Also the level is compatible with TTL level, which facilitates the connection with a TTL circuit
Maximum data transmission speed is 10 Mbps
The RS485 interface adopts the role of balancing driver and differential receiver so that the common mode disturbance immunity is improved, i.e. it has good noise immunity
Maximum 256 transceivers are allowed to connect to the bus. With this multi-station capability, a device network can be conveniently established via a single RS485 interface
Normally only two wires, a shielded twisted pair (STP), are needed in the half duplex network formed by the RS485 interface.

The main disadvantages are:

In the whole network only one node can transmit data to the bus at any one moment and all other nodes must be in receiving status. If there are two or more nodes transmitting data to the bus at the same time, all transmission fails
A special communication cable is needed. The maximum communication distance depends on communication cable type.

 

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