Doing serial upper machine appeared such problems, by can transfer box to connect the board, has a serial port the write function well, but suddenly not line, can host the didn't find I send data, on this side is measured by the USB logic analyzer serial port is not issued, but the detection write send the return value is the number of bytes, so write is the call is successful, and invoke qserialinfo: : isbusy () function, but still won't do, but also can use serial assistants found give, is connected to the can transfer box only occasionally hair not to come out, right, is the one moment can be sent to send not to come out? So it is a serial port line being used? Why use isbusy determine why or not?