jmcexx

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About jmcexx

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  1. Thank you. I would like to send the module to you to see what you can figure out. I'll remove the module.
  2. Thanks. Yes, we get exactly the same behavior at different baud rates. I know we tried at least 57600 baud.
  3. Yes, the scope plots are of pin 6 (TXD) referenced to pin 1 (GND) of the JTAG-SMT3-NC module.
  4. Yes, exactly. Each board has a separate module soldered to it. This is the only one with strange behavior. I'm interested to understand why before we move to producing larger volumes. Thanks, Ryan
  5. Thank you for the reply. I think you'll find your UART decoding is backwards. First bit should be a Low start bit (S), then 8 bit byte LSB first, followed by a high stop bit (P). My working example of 'A' was a very poor choice, since it is the same either way. Sorry for that confusion. Please see below with what I see for 'S', 'T', 'U', 'V', and 'W'. I really don't get what is going on with 'U'. Very strange. I'm quite interested to understand what could cause this. Thank you, Ryan
  6. 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: 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? UART trace U vs A.bmp
  7. I am considering powering the VDD input to the JTAG-SMT3-NC module from the USB supply instead of the device's power supply. Of course this will require a 3.3V LDO to bring VDD down. Do you see any issue with doing that? In my case, I would have: VDD - 3.3V from LDO from USB V+ (when cable plugged in) VREF_UART = 3.3V from system power supply (on when board powered up) VREF_JTAG = 1.8V from system power supply (on when board powered up) My intention is to allow the UART connection over USB to stay connected even when power cycling the board. I ask because all of the documents show VDD being supplied from the system, not USB. Thanks for any thoughts!