Serial Communiction error in Pyvisa

B Akshay · 04-18-2013, 12:58 AM

Hello,
I have writtern a small program to send AT command to the mobile phone.
The code is working fine. But i want to check the response of the AT command from the device i.e "OK". For that i have writtern a as follows,

Code:

        ser.write("at")
        time.sleep(0.5)
        for i in [1,2,3]:
              time.sleep(0.10)
              resp = ser.read()
              print resp
              print "\n i = ", i 
              if  resp != "\nOK":
                   print "NO Response"
              elif resp == "\nOK": 
                   print "Fine"
        time.sleep(10)

For the first iteration the code is working fine, But for the very next iteration it is giving the error. as follows,

Code:

 Iteration ->  1

at

 i =  1


 i =  2

OK

 i =  3
Fine

 Iteration ->  2


Traceback (most recent call last):
  File "C:\Working_Programs\PROG_D\My_prog.py", line 32, in <module>
    resp = ser.read()
  File "C:\Python27\lib\site-packages\pyvisa\visa.py", line 433, in read
    return self._strip_term_chars(self.read_raw())
  File "C:\Python27\lib\site-packages\pyvisa\visa.py", line 407, in read_raw
    chunk = vpp43.read(self.vi, self.chunk_size)
  File "C:\Python27\lib\site-packages\pyvisa\vpp43.py", line 840, in read
    visa_library().viRead(vi, buffer, count, byref(return_count))
  File "C:\Python27\lib\site-packages\pyvisa\vpp43.py", line 398, in check_status
    raise visa_exceptions.VisaIOError, status
VisaIOError: VI_ERROR_ASRL_FRAMING: A framing error occurred during transfer.
>>>

The baudrate is 115200.
Chunk size is default!!

I am always getting this error while reading the response from the device.

Thanks in advance for your time and input

theNbomr · 04-20-2013, 12:06 PM

The whole VISA layer seems like quite a heavy hammer for such a small nail. Perhaps try something more modest such as PySerial. Also, try communicating interactively with the device using a serial comm's terminal emulator. In Windows, I guess that would be hyperterminal, or some similar tool. The error message being reported suggests a problem with the serial communications at a low level: 'framing error', which very very rarely occurs repeatably, so I'm going to suggest that the problem is in the VISA layer somewhere, making it difficult diagnose.

--- rod.