RouterGod Guest Lecture Series

Mister Rogers Explains The RS 232 Pinout.

What a pleasure it is to have Mister Rogers back in our neighborhood.  His mere presence seems to have a calming effect on the crew here at RouterGod.  He seems so serene and gentle.  He is the epitome of grace.  When he walks his loafers appear so light.  He always smiles so sweetly.  Wearing his trademark sweater he has a far away twinkle in his eyes as he walks into our office.  He looks like an advertisement for ProZac.  Everybody loves Mister Rogers.  Let's join Mister Rogers as he explains the RS 232 Pinout:

Wasn't it nice of Mr. Rogers
to come here and teach
us about RS 232?


Well hello boys and girls!  Thank you for stopping by today.  Today we are going to talk about the RS 232 Interface.  Actually it's really not called the RS 232 anymore, now it's the EIA/TIA 232 interface.  It is used for serial connections from DTE devices like a personal computer to DCE devices like a modem.  Can you say modem?  I thought you could!  It uses a 25 pin DB 25 connector but only 8 of the wires are used.  The other 17 wires were bad and are being punished.

But I know that all of you are good boys and girls.  When we talk about what the RS 232 does, we do it from the perspective of the DTE.  Pin 2 is the TD or transmit data pin.  It carries the data to the DCE.  Pin 3 is the RD or receive data pin, it accepts incoming data from the DCE.  Pin 4 is the RTS or request to send,  when voltage is present that means that the receive buffer on the DTE is empty and it is asking the DCE to send more data.  Pin 5 is the CTS or clear to send, when voltage appears on that wire the DCE is saying "Hello Mr. DTE, my buffers are empty and I can accept more data".  Pins 4 and 5 are handling flow control.  Pin 6 is the DSR or data set ready.  When there is a signal on the DSR line, it means that the DCE or modem is ready.

Pin 7 is ground.  It is a reference point for the other signals.  Pin 8 is the CD or carrier detect.  And last but not least is pin 20, it is the DTR or data terminal ready.  Here is a table I made for you boys and girls, remember, this is from the perspective of the DTE:

Pin 2  TD DTE -----data-----> DCE
Pin 3 RD DTE <----- data---- DCE
Pin 4 RTS Oh Mister Modem!  My Buffers are Empty!
Pin 5 CTS Hey! The Modems Buffers Are Now Empty!
Pin 6 DSR The Modem is "Ready".
Pin 7 GRD  Just a Plain old ground, not very interesting...
Pin 8 CD The Modem has detected a carrier.
Pin 20  DTR I am Definitely Ready!

The call can be terminated by dropping the DTR or CD.  My goodness, you boys and girls were well behaved!  You are all so polite and I enjoyed our little visit.  Well, I'd love to stay, but I have to get back to my neighborhood.  Tomorrow I am going to bake a cake!

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