Problem Description:
Everything is normal when sending. Upon receipt, the interrupt can not enter interrupt polling undetectable flag. After confirming that the code is no problem to start checking circuit, finally found the reason. Problem external IO port having received a MAX3232 chip, and the test time for the patch to come out directly from the IO port usb to test the serial port chip, two chips connected interference with the received signal.
Solution :
Only use a communication mode, here as I do not usb to data line 232, so choose the MAX3232 chip removed.