1. Introduction to RS485 Author: Zhu Tao Date: 2008-10-24

2. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

3. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

4. Overview Definition [1] RS485, namely EIA-485, is an electrical specification of a two-wire, half-duplex, multipoint serial communication channel. supporting transmission in two directions simultaneously The transmission of data in both directions, but only one direction at a time. Refers to a communications line (network) that provides a path from one location to many. the process of sending data one bit at one time, sequentially, over a communication channel or computer bus.

5. Overview Use a differential balanced line over twisted pair Can span a large distance (up to 1200 m) Linear topology is the preferred recommended wires arrangement Not star or ring topology, because of signal reflection or excessively low or high termination impedance. RS485 topology

6. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

7. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

8. Features Often use the master-slave arrangement Not specify or recommend any data protocol (i.e. the overlaying protocol) Can be extended to full-duplex using 4- wire Components cost very low NO integral method to detect data collision (often be implemented using software) A full-duplex (or rarely double-duplex) system allows communication in both directions, and unlike half-duplex, allows this to happen simultaneously.

9. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

10. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

11. Comparison 摘自 [3]

12. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

13. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

14. Evaluation AdvantagesDisadvantages

15. Evaluation Advantages [2] 1. Small overhead (without defining the overlaying protocol, fault detect, etc.) 2. Cheaper hardware 3. Maximum data transmission speed is 10Mbps 4. Has good noise immunity 5. Maximum 256 transceivers are allowed to connect to the bus

16. Evaluation Disadvantages [2] 1. Only one node can transmit data to the bus at any one moment and all other nodes must be in receiving status, otherwise the transmission will fail (when 2 or more nodes transmit data simultaneously). 2. A special communication cable is needed. And the maximum communication distance depends on the type of the cable. 3. Need software to ensure no over 2 nodes transmit data simultaneously.

17. Evaluation Click here to see the detail here

18. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

19. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

20. Conclusion RS485 is used as the electrical layer for many well known interface standards, including Profibus and Modbus. Therefore RS485 will be in use for many years in the future. And in the TCN area, the train control system can be abstracted to a master- slaves model. So RS485 can be used.

21. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

22. Outline OverviewFeaturesComparisonEvaluationConclusionBibliography

23. Bibliography 1. http://en.wikipedia.org/wiki/EIA-485 http://en.wikipedia.org/wiki/EIA-485 2. http://www.metering.com/node/12618 http://www.metering.com/node/12618 3. http://www.lammertbies.nl/comm/info/RS- 485.html http://www.lammertbies.nl/comm/info/RS- 485.html http://www.lammertbies.nl/comm/info/RS- 485.html 4. 基于 RS485 的 25T 客车电源串行通信系统.pdf 5. 422 and 485 Standards Overview.pdf 6. The Art and Science of RS-485.pdf 7. EIA TIA-485-A an Overview.pdf

24. More can be seen in the next week. Thanks a lot!