Serial Port Programming Part 8 - DTR and DSR

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DTR and DSR are two control signals used by DTE(PC) and DCE(modem) to indicate they are alive.

DTR (Data Terminal Ready):

 Connected from DTE to DCE. This pin is output on DTE and input on DCE. High on this pin indicates that the DTE is alive and Low on this pin indicates that there is some problem with the DTE. When the terminal (PC) is turned ON, after going through self-test, it asserts the DTR signal.

DTR is present on pin20 of DB25 Connector and Pin4 of DE9 Connector.

DSR(Data Set Ready):

 Connected from DCE to DTE. This pin is output on DCE and input on DTE. High on this pin indicates that the DCE is alive and working and low on this pin indicates the problem with DCE. When the DCE(Modem) is turned ON, after going through self-test, it asserts DSR to indicate that it is ready to communicate.

DSR is present on pin6 of DB25 Connector and Pin6 of DE9 Connector.




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