So I have a standard RS232 serial port that is looped back to itself by simply running a wire from Tx to Rx. I'm testing loopback by running echo and cat in two separate terminals: cat /dev/ttyS1 echo 'hi' /dev/ttyS1 My issue is with the output. I would expect to see one 'hi' come back on the terminal running cat but instead I get this: hi 2 newlines hi 4 newlines hi 8 newlines hi 16 newlines hi 32 newlines hi.and so on until I ctrl+ c cat. After interrupting cat, if I run it again it will not output 'hi's until I run echo a second time. Is this normal? Any idea why I'm seeing this behavior?
D3 Informatika’); writeln(’3. Contoh program pascal. Contoh Program Kelipatan 5 Repeat Until Pada Pascal uses crt; var a: integer; begin clrscr; a:=5; repeat write(a,’ ‘); a:=a+5; until a>25; readln; end. PKK’); writeln(’2. D3 Elektro’); writeln(’4. Administrasi mahasiswa Program Administrasi_Mahasiswa; uses crt; const pkkspp = 400000; infospp = 600000; elekspp = 500000; bogaspp = 450000; ptikspp = 500000; pkkprak = 100000; infoprak = 500000; elekprak = 450000; bogaprak = 600000; ptikprak = 350000; sehat: real = 10000; var nm,jur: string; nojur: byte; tahun:integer; spp,prak: real; tot: real; begin clrscr; writeln(‘Administrasi Mahasiswa Fakultas Teknik dan Kejuruan’); writeln(‘===================================================’); write(‘Nama: ‘); readln(nm); writeln(‘Keterangan Jurusan: ‘); writeln(’1.
Edit: By newline, I mean ASCII 0x0A. There are no carriage returns in this output. Thanks to the second comment by Bruce, I was able to figure out the problem on my own. After running stty -a -F /dev/ttyS1, there were 3 options I found to contribute to the problem: 'echo', 'onlcr', and 'icrnl'.
Since this serial port is looped back to itself, here is what happened after running echo 'hi' /dev/ttyS1:. The echo command appends a newline to the end of the message by default, so 'hi' + LF is sent out to /dev/ttyS1. Because 'onlcr' was set, the serial device converted the LF to CRLF so the physical message sent out the Tx line was 'hi' + CRLF. Because 'icrnl' was set, the physical messaged received on the Rx line converted the CR to LF. So the message outputted by 'cat' was 'hi' + LFLF.
Because 'echo' was set, the message received on the Rx ('hi' + LFLF), was then sent back out on the Tx line. Because of onlcr, 'hi' + LFLF became 'hi' + CRLFCRLF.
Because of icrnl, 'hi' + CRLFCRLF became 'hi' + LFLFLFLF. Because of echo, 'hi' + LFLFLFLF was then sent out the Tx And so on. In order to fix this problem, I ran the following command: stty -F /dev/ttyS1 -echo -onlcr Disabling 'echo' prevents an infinite loop of messages and disabling 'onlcr' prevents the serial device from converting LF to CRLF on output. Now cat receives one 'hi' (with a single newline!) for each time I run echo. CR = carriage return (ASCII 0x0D); LF = line feed or newline (ASCII 0x0A).
I had a similar issue as well with concatenating files into a serial tty for testing. In addition to the accepted answer: If you're testing serial output by doing something like: cat somefile.txt /dev/ttyS0, it will have a good amount of unexpected byte data if you're testing for exact byte values.
With stty doing a simple stty raw -F /dev/ttyS0 will stop the terminal from inserting/replacing characters (e.g. Body combat. 0x0A. 0x0D 0x0A.). The raw flag changes the modes of the terminal so no input and output processing is performed.
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I suppose I should have mentioned it, but I tried minicom and it would not work properly. Not sure, but I get a blinking cursor at the bottom of the window similar to the tty1 output. I tried to exit and it hung. Had to kill its process from another tty.
From that clue I would say that the data is not being received at tty1. Take a look at the possibility that the data is not actually being transmitted or that it is being transmitted and the null modem cable is not sending it back. Could you run a test with a different cable where you connect the serial ports of two different computers? - Steve Stites.
Quote: Another test is to jumper the transmit and receive pins (pins 2 and 3 of either the 25-pin or 9-pin connector) of a test serial port. Then send something to each port (from the PCs keyboard) and see if it gets sent back.
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If it does it's likely the port with the jumper on it. Then remove the jumper and verify that nothing gets sent back.
Note that if 'echo' is set (per stty) then a jumper creates an infinite loop. Bytes that pass thru the jumper go into the port and come right back out of the other pin back to the jumper. Then they go back in and out again and again. Whatever you send to the port repeats itself forever (until you interrupt it by removing the jumper, etc.). This may be a good way to test it as the repeating test messages halt when the jumper is removed.
I think this answers my question! I just love you guys! Thanks for sharing information also after you find the soulution to your problems! I had a simmilar problem when trying to loop back on the /dev/tts/1 on a Linksys WRT54g, running DD-WRT.
I just couldnt get things to work, but after reading this thread I sent the router a: 'root@DD-WRT:# stty -F /dev/tts/1 -echo' and now things seems to work. I might need to remove some new line echo also, but that shouls be docunented in the stty documentation, I think. Tanks for sending me down the right trail!
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Loopback Test A loopback test can be used to troubleshoot serial communications. It can show problems in the serial port, the cable, or the software generating the messages without having to connect to third party hardware. By connecting the proper wires, a loopback test can verify the operation of serial communication. Loopback tests can be used for RS-232, RS-422, and RS-485 serial communication.
Serial Loop Back Test Software
For more information on RS-232, RS-422, and RS-485 see the. Note that not all serial devices, especially those with many connections on one card, allow hardware flow control on every serial output of the device. To perform a loopback test for RS-232, the TXD pin must be connected to the RXD pin. This allows the data to flow from the transmit to the receive pins.
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Since the communication is differential for RS-422 and RS-485, the TXD+ connects to the RXD+ and the TXD- connects to the RXD- pins. A more advanced loopback test that allows hardware flow control will need more pins connected to allow the flow control signals to be properly passed. For RS-232, the CTS and RTS pins must be connected along with the DTR and DSR pins. For RS-422 and RS-485, CTS+ should be connected to RTS+ and CTS- should be connected to RTS. For more information about National Instrument’s serial interfaces, visit. Connectors DE-9 (DB9) Connector The DE-9 connector is the most common serial connector.
This connector is found on National Instrument’s one and two port serial interfaces. Figure 1: Pinout diagram for DE-9 Connector To perform a loopback test with no hardware flow control, you will need to connect pins 2 and 3 for RS-232 and pins 4 to 8 and 5 to 9 for RS-422/485. These connections can be seen in red below (figure 2 for RS-232 and figure 3 for RS-422/485). When using hardware flow control, you will need to connect pins 4 to 6 and 7 to 8 for RS-232. Pins 7 and 8 are used for RTS/CTS hardware flow control where pins 4 and 6 are used for DTR/DSR hardware flow control.
For RS-422/485, you will need to connect pins 2 to 3 and 6 to 7. Both of these connections are required for RTS/CTS hardware flow control since RS-422/485 have differential connections. These connections can be seen in blue below (figure 2 for RS-232 and figure 3 for RS-422/485).
Figure 2: RS-232 female DE-9 plug with connections required for loopback test Figure 3: RS-422/485 female DE-9 plug with connections required for loopback test DB-25 Connector This connector is not as common as the DE-9 connector. This connector can still be used to perform a loopback test with a method similar to the one used for the DE-9 connector. Figure 4: Pinout diagram for DB-25 Connector Most of the pins on DB-25 connectors are not connected since only nine pins are used for RS-232, RS-422, and RS-485 communication. To perform a loopback test with no hardware flow control with a DB-25 connector, connect pins 2 to 3 for RS-232. For RS-422/485 connect pins 5 to 20 and 7 to 22. The required connections can be seen in red on figures 5 and 6.
For hardware flow control using RS-232, pins 4 and 5 must be connected along with pins 6 and 20. When using RS-422/485, pin 5 must connect to pin 20 and pin 7 must connect to pin 22. This will allow the loopback test to use the proper flow control lines. These connections can be seen in blue on figures 5 and 6.
Figure 5: RS-232 female DB-25 plug with connections required for loopback test Figure 6: RS-422/485 female DB-25 plug with connections required for loopback test 10P10C (RJ50) Connector This connector is most commonly found on National Instrument’s 4 port serial interfaces. The National Instrument 4 port serial interfaces come with 4 10P10C to DE-9 male converter cables.
Figure 7: Pinout diagram for RJ50 Connector It is not recommended to use the 10P10C connector by itself to perform a loopback test due to the small separation between pins. Using a 10P10C to DE-9 connector (Part Number 192190-01), a looback test can be performed using the methods described above. Performing a Loopback Test in Hyperterminal 1.
Create a new connection with any name and icon. Select the communications port you would like to test 3. Select the type of flow control you would like to use. Note that Xon / Xoff is software flow control and will only require that the TXD and RXD pins to be connected. Type a message using the computer's keyboard.
Any data that shows in Hyperterminal is received from the device. Performing a Loopback test in Measurement & Automation Explorer 1. Open Measurement & Automation Explorer and select the communications port you would like to use. Ensure the proper settings are selected for flow control. Save the settings with the Save button and then click the Open VISA Test Panel button.
Once the Test Panel window has opened, please select Input/Output. In the Basic I/O tab, click the Query command to send the default.IDN? The display window will then outline the write and read operations. The Test Panel should have successfully read the sent.IDN? Performing a Loopback test in LabVIEW Note: For a free evaluation copy of LabVIEW, visit 1. Start LabVIEW 2. Select Help»Find Examples.
Browse to Hardware Input and Output»Serial»Simple Serial.vi 4. Ensure the proper settings are selected and run the VI with the white run arrow on the toolbar. The “Response” indicator should display the.IDN? Related Resources. Kommentare. Hi, I'm trying a different type of environment of loopback. The loopback suggested by you is done locally.
Wondering how the below can be done:- Step 1: Tx characters from modem A to Modem B using hyper term. Step 2: modem B upon receiving the characters auto tx the characters received back to modem A. A summary of the enviorment is that whatever Modem A transmits, Modem B will do a auto loopback to modem A. Are there any AT commands that support this operation? Any advice is most appreciated. Regards, Zhiwei.
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