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I am not sure if the UART is extremely sensitive to ESD, or there could be a batch of uC that the UART is not functioning correct?
This is the 4th uC that I have done a circuit board rework on, and the UART quits working when a new uC is put on the board.
The first time this happened, I had a controller fail due to a voltage regulator failure. I replaced a 2nd and 3rd uC, and the UART would not work. I ended up building a new circuit with a 4th uC, and the UART magically started working with the same exact code. Thus, I assumed one of the components may have failed on the former circuit board, then moved on.
Now, with a functioning circuit (4th uC), I abused the uC by breaking off one of the pins. When replacing with the 4th uC, now the UART no longer works with a 5th uC.
In all cases above where the UART does not work, I am sending a signal to the uC which calls the UART ISR. By placing a break point within the ISR, and checking that the signal entering the uC is valid, the ISR break point is never hit. Thus, the signal is never triggering the ISR call for transmission.
I thought I wold add, the package marking is:
430AFE253
1ATG4
CHSPA
In addition, I put an AFE252 on the board, and the UART worked
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