- RS485 is a Differential interface
- Balanced transmission is used for RS485 communication
- RS485 is a Multi-point protocol. There is Single Master and multiple slaves
- RS485 supports Full Duplex as well as Half duplex option
- Data Rates up to 10Mb/s can be achieved
- Speed of RS485 is superior to RS422
- RS485 can be used up to distances of 1200m
- The maximum distance is generally decided by the capacitance over the line
- The maximum of devices supported are 32, can be more and it depends on transceiver characteristics. Study RS485 datasheets for more information
- Termination is used on both ends of the line
- There are biasing resistors as well as termination resistors required on the line
- By default, the RS485 transceiver will be set in Receiver mode. When the system wants to transmit data, Data enable (DE) will be pulled high
- Data Enable is Active HIGH and Receiver Enable is Active LOW
- Star and Ring topology cannot be used as the coenctivity becomes complex and due to impedance mismatch this may cause reflections
- RS485 transceivers are used between micro controller and physical side for the RS485 transmission, UART is used on the micro controller side for connecting to RS485 transceiver
- RS485 Transceivers in the market:
- SN65HVD485E from Texas Instruments,
- LTC2856-2 from Linear Technology,
- ISL32704E from Intersil
- There are several other vendors as well
- While selecting the RS485 transceivers, designer consider the following options,
- Operated supply
- Over voltage protection
- ESD protection
- Galvanic isolation
- Fault tolerance options like fault voltage
- Data Rate consideration
- Hot plugging feature
- Number of transceiver options within a chip
- Cost criteria