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Old 04-14-2009, 12:32 AM   #1
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Location: Balikpapan, Indonesia
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Unhappy Serial port on openSUSE 11.1

Hi All,

I'm actually not a 'really' newbie in Linux, but it's already been a while since I used openSUSE 10.2, I don't really touch Linux until now.

I just installed openSUSE 11.1 in my PC. And I found no problem in installing it. But later i realized that the on-board serial port is not working. I've tried to see the configuration using setserial, and the result is like this:

# setserial -G /dev/ttyS0
/dev/ttyS0 uart 16550A port 0x03f8 irq 4 baud_base 115200 spd_normal skip_test
I assumed that it should be working fine, but actually I can't connect to other equipment using it. For example, I tried to connect to a cisco device using minicom, but it failed to connect. It seems like Linux (or the program) doesn't recognize the port.

Does anyone here have any idea on how to make it work? Thanks in advance.
Old 04-15-2009, 11:25 AM   #2
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A number of possibilities exist. Since setserial recognizes the port, and since the numbers that is report look completely normal, I am going to work on the premise that the device and attendant driver are present and working. The connection to your external device require that a proper cable (and not all RS-232 cables are created equal) is installed. Usually, this means a cable with at least a ground, Tx, and Rx conductors wired correctly. Depending on the device and style of connectors, you may have to cross over the Tx & Rx pins. You haven't stated what you do know about the required cabling, so I leave it to you to confirm that you know it is cabled correctly, or find out from documentation for the device.
You can verify that the serial port transmits and receives by looping the Tx pin back onto the Rx pin. In almost all cases this means jumpering pin 2 to pin 3 of the serial port. Having done this, start up a terminal emulator such as minicom (or C-Kermit, which I prefer), and when in 'connected' mode, type some keystrokes. The sent data should be echoed back through the connector & cable, and appear as incoming data. Seeing this happen confirms that the serial port and driver are working. You can use a short piece of wire, paper clip, screwdriver tip, or whatever to short the two pins for this test. It should go without saying that you need to use the correct connector on each device, but more than one person has used the wrong one. Don't ask me how I know this.
Having verified that the serial port, driver, and cable are correct, you will then need to configure the serial port to use the correct communications parameters, according to the requirements or the external device with which you want to communicate. These parameters should be documented, but if not, 9600 baud, No parity, 8 data bits, and one stop bit is a very common configuration. There are a smallish number of other bit rates, and trying the faster rates first is more likely to bring success. When the bit rate is correct, you will likely start to see some recognizable communications, but possibly interlaced with garbage characters. This indicates that you need to adjust the word size and or parity settings. Again, given tha small number of possibilities, trial and error adjustment can usually home in on the correct settings.

--- rod.


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