A STM32 customer feedback, when the STM32F407V chip is frequently turned on and off frequently, the FLASH will be illegally rewritten, and various exceptions occur (the whole chip is erased, the interrupt vector table is rewritten, the write protection is cleared, etc.) .
After communicating with customers, I learned:
1, they are the project before the continuation, some simple modifications of the software and hardware. There have been no similar problems with previous projects.
2. Confirm that the power-off time is sufficient, that is, all VDD returns to 0 after power-off; the timing of power-on is also normal.
3. The schematic diagram refers to the reference design of the ST related development board.
4, measuring the working voltage, in addition to detecting a little jitter when powering up, everything else is normal. Try to get them to improve the power-up circuit and get rid of this jitter. Experimenting again, similar problems still occur.
According to the preliminary judgment of the phenomenon, the abnormality seems to be unrelated to the hardware. Then, the client code is deleted and the following experiment is performed:
1, remove the APP part of the code, leaving only the IAP code. Do the same experiment and reproduce the problem.
2, further cut the program, remove all the parts of the program related to flash and OPTION BYTE, do the same experiment, the problem remains.
3, no move, then delete the code, or block the code. Do code replacement based on different STM32 libraries. The problem is always the same.
There is no progress in this issue, so I have to ask the ST chip designer for further confirmation to see if the chip is really bad. At the same time, the customer's hardware engineers are asked to reconfirm the consistency of their hardware circuits and schematics. We suspect that their hardware has faulty components, especially around the MCU.
Later, the customer engineer feedback, the PDR_ON pin of STM32F407, the components on the board are inconsistent with the schematic. They installed both R47 and R48 [as shown below], which is equivalent to a 0.6v voltage on PDR_ON, which is to turn off the MCU internal reset.
It can be said that there is no way for the mountains and waters to be dumb, and there is still a village in the dark, and it seems that the problem should be related to the internal reset.
See the STM32F407 data sheet for information.
From the above specification, the internal reset circuit of STM32F407V can be selectively turned on or off. If you choose to turn off the reset circuit inside mcu, you need to externally connect a reset monitoring circuit to ensure that the MCU is in the reset state until VDD reaches the normal working voltage. . Here, the customer does not intend to turn off the internal reset, and there is no corresponding power supply monitoring reset circuit. In this case, according to the manual description, the PDR_ON pin can be connected to VDD. Specifically here, remove the 1k ohm resistor of R48. The redo experiment was repeatedly verified and the abnormality disappeared.
For STM32, some of the PDR_ON pins are encapsulated, and some packages are not exported. If the internal reset function is enabled by default, if you pull it out, you should also pay attention to some models that are pulled low to enable internal reset, and some are pulled high to enable internal reset. Please pay attention to this when designing and using.
Similar to small details, it is easy to be ignored. The reason for finding a neglected situation is often a very tossing, tortuous and painful thing. This kind of situation can't be completely avoided for engineers. After all, we are human beings. Therefore, pay more attention to and accumulate in peacetime. It is especially important to keep calm analysis and rational judgment when encountering problems. Do not be tempted to doubt the quality of the chip and make development and debugging stagnant.
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