Appendix 1 Definition of Terms
A-5
(11) Half Duplex Communication
Two-way communication is available, however simultaneous communication of transmission &
receiving isn’t available. This communication type is applied to RS-485 for instance. It is used a lot
for multi-drop communication type which communicates via one signal line by several stations. Half
Duplex Communication results from the transmission characteristic performed by stations one by one
not allowing simultaneous transmission by multi stations due to the data damage of data impact
caused by the simultaneous multi-transmission of the stations. The figure below shows an example
of structure based on Half Duplex Communication. Each station in communication with the terminal
as linked with each other can send or receive data via one line so to execute communication with all
stations, where multi-sever is advantageously available.
(12) Full Duplex Communication
Two way-communications of simultaneous transmission & receiving is available. This communication
type is applied to RS-232C & RS-422. Since the transmission line is separated from the receiving line,
simultaneous transmission & receiving is available without data impact, so called as Full Duplex
Communication. The figure shows an example of structure based on RS-422 of Full Duplex
Communication. Since transmission terminal of the client station and receiving terminals of the sever
stations are connected to one line, and transmission terminals of the sever stations are linked with
receiving terminal of the client station, the communication between sever stations is unavailable with
the restricted function of multi-sever.
TX RX
RX RXRXRX TX TXTX TX
TX RX
RX RXRXRX TX TXTX TX
Client
Server ServerServerServer
Client
Server Server Server
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