Why can't MCU receive the data sent by SIM900A module?

Debugging with atomic program succeeded, mine didn't succeed. . . It is estimated that it is related to the computer serial debugging assistant and the underlying driver. . I use the computer and sim900a to send and receive short messages normally, and then the SIM900A module is constantly powered on, and the serial port line is connected to the serial port of the warship development board through live operation. Warship development board, communication with SIM900A module is normal. The serial port of ship development board can receive the information sent by SIM900A serial port. .

After the communication between the computer serial debugging assistant and the SIM900A is normal, the SIM900A runs online and jumps the serial port of the warship development board. Communication is normal at this time.

I don't know the computer serial debugging assistant, how to run at the bottom and what code to execute. . . Knowing this can solve it, but I have never figured out how to write the interface of the computer serial debugging assistant and what the bottom layer does. . Copy the code of Atomic Brother directly and do touch-screen mobile phone test. .

Let me know if you solve it. I am learning interface programming now. . . .