Doubt with Pin 4 and 7 of DB9 9PIN RS232

What is the function of Pin 4 and 7 of the 9 pin DB9 RS232 in layman term?

Which pin is responsible for ceasing all activities between the computer and the device when activated.

Thanks

zenniz said:

What is the function of Pin 4 and 7 of the 9 pin DB9 RS232 in layman term?

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PIN 4 - DTR Data Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE.

PIN 7 - RTS Request To Send. Raised by DTE when it wishes to send. Expects CTS from DCE.

PIN 9 - RI Ring Indicator. Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer.


The above DTR and RTS lines are used in Hardware Flow Control, sometimes along with the following depending on the implementation:

PIN 6 - DSR Data Set Ready. Raised by DCE to indicate ready.

PIN 8 - CTS Clear To Send. Raised by DCE in response to RTS from DTE.


The RI line is simply an indicator of when a Ring is detected, used to auto answer incoming connections.

Tech Stuff - RS-232 Cables, Wiring and Pinouts

zenniz said:

Which pin is responsible for ceasing all activities between the computer and the device when activated.

Click to expand...

It depends on the perspective of device type you are referring to, DCE or DTE.

For example a PC is typically a Data Terminal Equipment (DTE) and a modem is the Data Communications Equipment (DCE).

RS232 serial cables pinout

RS232 flow control and handshaking


BigDog