pySerial inWaiting returns incorrect number of bytes

Question

I\'ve got a simple program to test serial functionality. My serial device reacts to two inputs. If the user enters \'a\', it responds with \'fg\'. If the user enters anythin

Answer 1

it could be because the baudrate is really slow. You are processing the inwaiting() call before the second byte gets to the buffer. When you do ser.read(2) it waits(blocks) until 2 bytes have been received thus why it works. Try setting a timeout of 1 second, that should fix your problem.

ser = serial.Serial(
    port = '/dev/ttyUSB0',
    baudrate = 9600,
    parity = serial.PARITY_NONE,
    stopbits = serial.STOPBITS_ONE,
    bytesize = serial.EIGHTBITS,
    timeout=1 # add this
    )
ser.write('a')
byteData = ser.read(1) # read one, blocking
byteData += ser.read(ser.inWaiting())

print byteData

ser.close()