Computer Interfacing
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Why DTR is used for Fullduplex Communication


       Computer Interfacing Forum Index -> RS422 and RS485
Author Message

Mar 03, 2010 7:24 pm

I am designing a RS485 to RS232 Converter, I am using a half-duplex IC SN75176. To make it a full-duplex, can i use DTR pin to control the data flow? Will DTR pin of PC helps in select the device to send the data or recive the data?
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Joined: 20 Apr 2009
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Location: Los Angeles

Mar 15, 2010 9:55 pm

DTR can help you determine signal direction. However, this relies on the software in the PC actually using the DTR pin. For example, in hyperterminal, you can connect with or without hardware flow control. Some RS232 to 485 converters allow you to choose to use the DTR pin this way. In general, you may wish to make the presense of data transmitted fromt the PC (RS232 side) cause the RS485 transceiver to go to output state. Then you don't need DTR. You do need well behaved software that knows when to send or not, such as in a command/reponse protocol.

I assume above that you are doing '2 wire' as opposed to '4 wire' RS485.

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