ARM serial port hardware and software testing

I have been deeply affected by serial ports since 51. The MAX232 I bought from Huaqiang was originally broken. I thought there was something wrong with my circuit or schematic. Since there was no good serial port, I thought of starting from myself, from the smallest system board to the peripheral circuit. Later, it was verified that the chip was not working. Later, I found that the male and female connectors were also particular in the design of the circuit. When designing ARM, the level conversion chip also needs to be replaced with MAX3232, that is, a chip with a driving voltage of 3.3V.

Next, we will make some summary about serial port debugging:

1. Power on the newly soldered board and use a multimeter to test the voltage signal generated by MAX3232. The 2nd pin of MAX3232 is about +10V to ground, the 6th pin is about -10V to ground, the 16th pin is about +5V, and the 15th pin is grounded.

2. Open My Computer->Management->Device Manager->Port->Communication Port, double-click, enter "Port Settings", check the baud rate and some other settings, mainly the baud rate, which must be the same as the software to be debugged.

3. Make sure whether the serial port you want to connect to your board is male or female. If the design is male/female, and you weld female/male, it will not work. It is equivalent to swapping the original 2nd and 4th pins with 3rd pin as the axis of symmetry; swapping 1st and 5th pins, because we usually need 2nd, 3rd and 5th pins for communication. If the 4th pin becomes 2nd pin after swapping; the 5th pin becomes 1st pin, it is equivalent to not connecting anything at all. It will definitely not work when tested.

Generally, if you use a female connector to connect to MAX3232 on the board, you should connect to pins 2 (TX), 3 (RX), and 5 (GND). If you use a male connector to connect to MAX3232 on the board, you should connect to pins 4 (RX), 3 (TX), and 1 (GND).
Note: Some male connectors do not have numbers, so you can just number them yourself: the male connector is facing you, numbered 1, 2, 3, 4, and 5 from left to right.

4. Test with MAX3232 chip and serial debugging assistant

I. If you are sure that you have connected the above correctly, short-circuit the 2nd and 3rd pins of the female connector on the extension cable, and use the serial port debugging assistant. If it can send and receive messages automatically, it means that there is no problem with the extension cable.

A MAX3232 can have two serial ports. Before performing the following operations, first determine which serial port you are using.

II. Next, power on the board and short-circuit the corresponding R*X and T*X on the end connected to ARM (* indicates which serial port it is, because two serial ports are connected). If it can send and receive signals automatically after short-circuiting, it means that there is no problem with your serial port hardware.

51 is connected like this:

ARM is connected like this: