In use with NVIDIA Jetson development board, because the GPIO port is not enough to use, so want to expand the GPIO GPIO module through the serial port, so you need to communicate with a serial port turn GPIO module development board, communication content in general is as follows: the main request frame (hexadecimal) : 01 05 00 05 00 FF 9 c 3 b, from a standing response frame (hexadecimal) : 01 05 00 05 00 FF 9 c 3 b, which is the main development board, transfer from station is a serial port GPIO module, but in the process of serial communication, there is a problem, is to send the request frame can be normal to send, also can achieve a serial port turn GPIO control module, but in turn read serial GPIO module returns the response of the frame, the existence of incomplete data read, like should return is 01 05 00 05 00 FF 9 c 3 b, but I read only 7 bytes (05 00 05 00 FF 9 c 3 b) or less (0 05 00 FF 9 c 3 b, 5 00 FF 9 c 3 b), didn't find out where the problem to find a lot of reasons, have great god know this kind of situation is how to return a responsibility? How should solve?