RN8209+stm32+spi communication always receives 0xff

Lesson for next time: Before making a finished board, it is recommended to make a demo board first. The bigger it is, the more time it saves. As long as it is within 10*10, it is the same price. But it must be the most complete version of this chip or function, and the interface must be reserved for debugging!

This time the rn8209-demo board:

1After the PCB layout is completed, you can add more interfaces.

2spi/serial port conversion switch

3 pulse output pins

Of course, unless you are very sure about this circuit, there is no need to make this demo board. ​

RT (as the title says), the information about RN8209 is very detailed, but there are only two programs. I encountered a problem during debugging and couldn't find the solution after searching for a long time. I always suspected that there was something wrong with the program, but there were no other ready-made programs to refer to. I had no choice but to find the problem bit by bit.

Finally, I found some other clues in a post I searched on Google:

Filter capacitor: existence is important, and value is also important http://xzpeter.org/?p=98

Following this life-saving straw, I debugged the hardware and suspected that the filter capacitor was too small and the voltage fluctuation was too large (the official user manual said that the fluctuation must be around +-30mv), causing the chip to not work. I used my hand to press the power supply pins of the chip, avcc and vss, dvcc and vss (the human body is a huge capacitor). It worked, and the chip ID returned 8209 when it was read! Victory! Then I moved my hand and pressed it on the chip, and it worked! ??? Then it was not a problem with the filter capacitor, but a cold solder joint! Finally found the problem!

It turned out that there was not enough solder on the new PCB board, and the chip pins were poorly soldered! The chip did not work at all! The program also ran normally!