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Train HDLC synchronous communication working mode

HDLC protocol is a common protocol for train communication. In order to reduce the number of signal lines, NRZI coding format is usually used.

The following diagram shows half-duplex HDLC communication based on RS-485 bus for train TCMS system or TMS system:

 

 

Some trains will also use RS-422 full-duplex mode, as shown in the following figure: