Pyserial - send and receive characters through linux serial port

Discussion in 'Python' started by terry, Apr 26, 2008.

  1. terry

    terry Guest

    Hi,

    I am trying to send a character to '/dev/ttyS0' and expect the same
    character and upon receipt I want to send another character. I tired
    with Pyserial but in vain.

    Test Set up:

    1. Send '%' to serial port and make sure it reached the serial port.
    2. Once confirmed, send another character.

    I tried with write and read methods in Pyserial but no luck.

    Can you help?

    Thanking you all.
    T
     
    terry, Apr 26, 2008
    #1
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  2. En Fri, 25 Apr 2008 20:22:37 -0300, terry <> escribió:

    > I am trying to send a character to '/dev/ttyS0' and expect the same
    > character and upon receipt I want to send another character. I tired
    > with Pyserial but in vain.


    I assume you have a device attached to /dev/ttyS0 that echoes back the
    received characters?

    > Test Set up:
    >
    > 1. Send '%' to serial port and make sure it reached the serial port.
    > 2. Once confirmed, send another character.
    >
    > I tried with write and read methods in Pyserial but no luck.


    Check the communication parameters (baud rate, parity, etc.), cable,
    connectors, your device... AFAIK a lot of people is using pyserial so I'd
    look the problem elsewhere. Try posting a short code example showing your
    problem.

    --
    Gabriel Genellina
     
    Gabriel Genellina, Apr 26, 2008
    #2
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  3. terry wrote:

    > I am trying to send a character to '/dev/ttyS0' and expect the
    > same character and upon receipt I want to send another character.
    > I tired with Pyserial but in vain.


    Pyserial works very well for me (despite the device I connect to has
    quite a screwed protocol and implementation).

    > Test Set up:
    >
    > 1. Send '%' to serial port and make sure it reached the serial
    > port. 2. Once confirmed, send another character.
    >
    > I tried with write and read methods in Pyserial but no luck.


    Are you actaully trying to get lucky by doing this, or are you
    observing a specific problem, e.g. nothing is received or wrong
    characters are received? Also, by what are they received?

    Regards,


    Björn

    --
    BOFH excuse #139:

    UBNC (user brain not connected)
     
    Bjoern Schliessmann, Apr 26, 2008
    #3
  4. terry

    terry Guest

    On Apr 26, 8:21 am, Grant Edwards <> wrote:
    > On 2008-04-25, terry <> wrote:
    >
    > > I am trying to send a character to '/dev/ttyS0' and expect the
    > > same character and upon receipt I want to send another
    > > character. I tired withPyserialbut in vain.

    >
    > Pyserialworks.  I've been using it almost daily for many
    > years.  Either your program is broken, your serial port is
    > broken, or the device connected to the serial port is broken.
    >
    > > Test Set up:

    >
    > > 1. Send '%' to serial port and make sure it reached the serial port.
    > > 2. Once confirmed, send another character.

    >
    > > I tried with write and read methods inPyserialbut no luck.

    >
    > > Can you help?

    >
    > Ah yes, the problem is in line 89 of your program.
    >
    > We've no way to help if you don't provide details. If you
    > really want help, write as small a program as possible that
    > exhibits the problem.  I'd like to emphasize _small_. The
    > larger the program the less likely people are to look at it,
    > and the less likely they are to find the problem if they do
    > look at it.
    >
    > Much of the time the exercise of writing a small demo program
    > will lead you to the answer.  If not, then post it, along with
    > the output from the program that shows the problem.
    >
    > Then we can tell you what you did wrong.
    >
    > --
    > Grant Edwards                   grante             Yow! I'm also against
    >                                   at               BODY-SURFING!!
    >                                visi.com            


    Here is the code.

    """Open serial connection"""
    def openSerialConnection(self,serpt):
    try:
    s1 = serial.Serial(serpt,timeout=10)

    except:
    self.print_u("Failed to open serial port %s. " %serpt)

    def enterThroughSerialPort(self,serpt):
    s1 = serial.Serial(serpt,timeout=10)
    self.print_u('Sending !!!!..')
    while True:
    s1.write('*')
    c = s1.read(1)
    if c:
    self.print_u('Found "*" ')
    break
    print c
    s1.write('enter\r')
    s1.read('login')

    if __name__ == '__main__':
    serpt = '/dev/ttyS0'
    x.openSerialConnection(serpt)
    # funtion to reboot the device goes here ---#
    x.enterThroughSerialPort(serpt)

    After opening the serial connection, the device is rebooted followed
    by sending '*' to serial port and reading back the same. I seem to
    have problem while trying to read '*' back from serial port. First of
    all I am not sure if serial port received the '*'.

    Thanks!
     
    terry, May 2, 2008
    #4
  5. terry

    terry Guest

    On May 2, 10:26 am, terry <> wrote:
    > On Apr 26, 8:21 am, Grant Edwards <> wrote:
    >
    >
    >
    >
    >
    > > On 2008-04-25, terry <> wrote:

    >
    > > > I am trying to send a character to '/dev/ttyS0' and expect the
    > > > same character and upon receipt I want to send another
    > > > character. I tired withPyserialbut in vain.

    >
    > > Pyserialworks.  I've been using it almost daily for many
    > > years.  Either your program is broken, your serial port is
    > > broken, or the device connected to the serial port is broken.

    >
    > > > Test Set up:

    >
    > > > 1. Send '%' to serial port and make sure it reached the serial port.
    > > > 2. Once confirmed, send another character.

    >
    > > > I tried with write and read methods inPyserialbut no luck.

    >
    > > > Can you help?

    >
    > > Ah yes, the problem is in line 89 of your program.

    >
    > > We've no way to help if you don't provide details. If you
    > > really want help, write as small a program as possible that
    > > exhibits the problem.  I'd like to emphasize _small_. The
    > > larger the program the less likely people are to look at it,
    > > and the less likely they are to find the problem if they do
    > > look at it.

    >
    > > Much of the time the exercise of writing a small demo program
    > > will lead you to the answer.  If not, then post it, along with
    > > the output from the program that shows the problem.

    >
    > > Then we can tell you what you did wrong.

    >
    > > --
    > > Grant Edwards                   grante             Yow! I'm also against
    > >                                   at               BODY-SURFING!!
    > >                                visi.com            

    >
    > Here is the code.
    >
    > """Open serial connection"""
    >         def openSerialConnection(self,serpt):
    >             try:
    >                 s1 = serial.Serial(serpt,timeout=10)
    >
    >             except:
    >                 self.print_u("Failed to open serial port %s. " %serpt)
    >
    >         def enterThroughSerialPort(self,serpt):
    >             s1 = serial.Serial(serpt,timeout=10)
    >              self.print_u('Sending !!!!..')
    >              while True:
    >                 s1.write('*')
    >                c = s1.read(1)
    >                if c:
    >                   self.print_u('Found "*" ')
    >                     break
    >             print c
    >              s1.write('enter\r')
    >              s1.read('login')
    >
    > if __name__ == '__main__':
    >     serpt = '/dev/ttyS0'
    >     x.openSerialConnection(serpt)
    >     # funtion to reboot the device goes here ---#
    >     x.enterThroughSerialPort(serpt)
    >
    > After opening the serial connection, the device is rebooted followed
    > by sending '*' to serial port and reading back the same. I seem to
    > have problem while trying to read '*' back from serial port. First of
    > all I am not sure if serial port received the '*'.
    >
    > Thanks!- Hide quoted text -
    >
    > - Show quoted text -


    This is the err message I received:

    c = s1.read(1)
    File "/usr/local/lib/python2.5/site-packages/serial/serialposix.py",
    line 275, in read
    ready,_,_ = select.select([self.fd],[],[], self._timeout)
     
    terry, May 2, 2008
    #5
  6. En Fri, 02 May 2008 15:44:09 -0300, terry <> escribió:
    > On May 2, 10:26 am, terry <> wrote:
    >> On Apr 26, 8:21 am, Grant Edwards <> wrote:
    >>
    >> > Much of the time the exercise of writing a small demo program
    >> > will lead you to the answer.  If not, then post it, along with
    >> > the output from the program that shows the problem.

    >>
    >> Here is the code.
    >>
    >> """Open serial connection"""
    >>         def openSerialConnection(self,serpt):
    >>             try:
    >>                 s1 = serial.Serial(serpt,timeout=10)
    >>
    >>             except:
    >>                 self.print_u("Failed to open serial port %s. " %serpt)
    >>
    >>         def enterThroughSerialPort(self,serpt):
    >>             s1 = serial.Serial(serpt,timeout=10)
    >>              self.print_u('Sending !!!!..')
    >>              while True:
    >>                 s1.write('*')
    >>                c = s1.read(1)
    >>                if c:
    >>                   self.print_u('Found "*" ')
    >>                     break
    >>             print c
    >>              s1.write('enter\r')
    >>              s1.read('login')
    >>
    >> if __name__ == '__main__':
    >>     serpt = '/dev/ttyS0'
    >>     x.openSerialConnection(serpt)
    >>     # funtion to reboot the device goes here ---#
    >>     x.enterThroughSerialPort(serpt)
    >>
    >> After opening the serial connection, the device is rebooted followed
    >> by sending '*' to serial port and reading back the same. I seem to
    >> have problem while trying to read '*' back from serial port. First of
    >> all I am not sure if serial port received the '*'.

    >
    > This is the err message I received:
    >
    > c = s1.read(1)
    > File "/usr/local/lib/python2.5/site-packages/serial/serialposix.py",
    > line 275, in read
    > ready,_,_ = select.select([self.fd],[],[], self._timeout)


    If you want some help, you have to help us to diagnose the problem.
    The above lines are just a small excerpt of the complete error report that
    surely you got; usually it includes the exception *type*, the exception
    *value*, and the whole *stack trace*. Now we have to *guess* what happened
    in that select call.
    Also, when posting code, try to post the *actual* code you run - copy and
    paste it. Do not retype it again. The code you posted has indentation
    errors, uninitialized variables...
    Try to make a *small*, runnable example that reproduces the problem;
    remove anything that isn't esential to the issue being discussed. Write
    down what is your expected behaviour, and what actually happens. If the
    program halts due to an error, copy the *whole* report including the
    exception type, message, and the complete traceback.

    In this particular case, due to the serial device, it's improbable that
    someone will be able to execute your program, but anyway try to write the
    example code. Sometimes you may find the problem yourself just by trying
    to write the example.

    A few notes on the code:

    - don't create many Serial objects; create only a single instance and use
    it everywhere it is needed. (That is, instead of using '/dev/ttyS0' as an
    argument, pass the Serial object already created, or save it as an
    instance attribute: self.serial = Serial(...) )

    - ensure you're using the right protocol parameters (baud rate, bits,
    parity...) for the device. That's why it helps to create the Serial object
    in a single place.

    --
    Gabriel Genellina
     
    Gabriel Genellina, May 3, 2008
    #6
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