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Old 08-19-2011, 12:48 PM   #1
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how to prove working of RS-232 full modem working PC to PC and LOOP BACK

Hello there I am a newbie trying to prove the working of RS-232 Full modem and also one RS-422( RX,TX,RTS,CTS)

These 2 ports are on a custom designed board and I need to prove the working.I am able to confirm the working at register level but I need to prove the working using softwares like Minicom or any other custom program.

How can I prove the working of these ports from one PC to a different PC using DB 9 connections and LOOP BACK too

Can someone help me with this ..Do I need to use any extra hardware to prove the working of this in Linux.

Thanks and regards

Last edited by getasif; 08-19-2011 at 01:00 PM. Reason: additional info
Old 08-20-2011, 07:00 AM   #2
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With a null modem serial cable you can test the RS-232 port between your board and another PC. minicom will work and you can set hardware flow control as desired.

RS-422 will require a converter on the PC side and two twisted pair wiring between the board and PC. For short runs you can use 4 individual wires and hand twist ( ~2-3 twists per inch) . You can use minicom.
Old 08-20-2011, 10:58 AM   #3
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You cannot prove full functionality of a modem without using a telephone connection (in other words, try it. If it works, it works, if not, it doesn't work). You can exercise the RS-232 serial port incrementally. Place a loopback jumper between pins 2 & 3 of the serial port D-sub connector. This will link the Tx signal back into the Rx pin. With any terminal emulator, press keys and observe that the keystrokes are read back to the terminal. If you connect a proper cable (normally a 'straight' cable) between the serial port and modem, you should be able to verify that the modem, serial port and cable are functional by observing that modem commands can be received, echoed, and interpreted by the modem. Again, this is done by typing modem commands in a terminal emulator, and observing the modem response to the commands.
--- rod.


linux, minicom, rs232, serial port

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