code: public function confStopBits($length)
      {
          if ($this->_dState !== SERIAL_DEVICE_SET) {
              trigger_error("Unable to set the length of a stop bit : the " .
                            "device is either not set or opened", E_USER_WARNING);
  
              return false;
          }
  
          if ($length != 1
                  and $length != 2
                  and $length != 1.5
                  and !($length == 1.5 and $this->_os === "linux")
          ) {
              trigger_error(
                  "Specified stop bit length is invalid",
                  E_USER_WARNING
              );
  
              return false;
          }
  
          if ($this->_os === "linux") {
              $ret = $this->_exec(
                  "stty -F " . $this->_device . " " .
                      (($length == 1) ? "-" : "") . "cstopb",
                  $out
              );
          } elseif ($this->_os === "osx") {
              $ret = $this->_exec(
                  "stty -f " . $this->_device . " " .
                      (($length == 1) ? "-" : "") . "cstopb",
                  $out
              );
          } else {
              $ret = $this->_exec(
                  "mode " . $this->_winDevice . " STOP=" . $length,
                  $out
              );
          }
  
          if ($ret === 0) {
              return true;
          }
  
          trigger_error(
              "Unable to set stop bit length : " . $out[1],
              E_USER_WARNING
          );
  
          return false;
      }
docs: Sets the length of stop bits.
  
  @param  float $length the length of a stop bit. It must be either 1,
  1.5 or 2. 1.5 is not supported under linux and on
  some computers.
  @return bool