I'm using JTAG-SMT3-NC for JTAG and UART on a custom board. One of the boards has a very strange behavior when sending UART serial to the board. The character 'U' doesn't work, but all other keys work fine.
Digging into it a bit further, I can see with a scope that the UART signal is incorrect for the letter 'U'. Please see attached scope plot. The upper (white) trace is when the 'U' key is pressed. Please compare this to the lower (yellow) is the 'A' key. Manually decoding, the 'A' waveform is correct (0x41), but the 'U' is incorrect (0xd5 instead of 0x55).
A few other notes:
Same behavior on two totally separate laptops (windows10)
Same behavior at different baud rates.
115200 baud, 1N8 normally used.
The 'U' key works as expected on ~10 other boards we used. Seems like something "happened" with this one.
All other letters appear correct, and have their MSB cleared.
Could anyone think what might cause this behavior?
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jmcexx
Hi,
I'm using JTAG-SMT3-NC for JTAG and UART on a custom board. One of the boards has a very strange behavior when sending UART serial to the board. The character 'U' doesn't work, but all other keys work fine.
Digging into it a bit further, I can see with a scope that the UART signal is incorrect for the letter 'U'. Please see attached scope plot. The upper (white) trace is when the 'U' key is pressed. Please compare this to the lower (yellow) is the 'A' key. Manually decoding, the 'A' waveform is correct (0x41), but the 'U' is incorrect (0xd5 instead of 0x55).
A few other notes:
Could anyone think what might cause this behavior?
UART trace U vs A.bmp
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