Please check setting 6 data bits in 'open' method. Thanks.

Shouldn't case 6: use CS6? Here is the current code:

  switch (self.numberOfDataBits) {
        case 5:
            options.c_cflag |= CS5;
            break;
        case 6:
            options.c_cflag |= CS5;
            break;
        case 7: 
...
