public void set_pwm_v(short value) throws IOException {
      byte[] data=new byte[3];
      data[0]=(byte)SET_PWM_V;
      data=_shortToByteArray(data,value,1);
      byte[] result = this.sendAndReceive(data, COM_TIMEOUT, 1);
      if (result.length==0) throw new IOException("no answer from device");
      if (result[0]!=0) throw new IOException("device error: "+result[0]);
    }