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MSP430FR6047: It is booting when connected to UART without power connection.

JunChul Lee
Intellectual 260 points
Part Number: MSP430FR6047
Other Parts Discussed in Thread: EVM430-FR6047,

hello
Our company is producing a custom board based on EVM430-FR6047.
In the custom board, MSP430fr6047's P2.0: UCA0TXD, P2.1: UCA0RXD pins were configured as debug UART ports.

The debug UART part of the custom board is as follows.


And, to check degug UART operation, I programmed FW for TEST.
However, when only USBtoUART is connected to the custom board while all other cables, including the power source, are disconnected, the msp430fr6047 starts booting.

And, debugging is output from the USBtoUART port without power connection.

I'm inquiring because I don't understand why it boots by just connecting the UART even though the power is not connected.

The HW person in charge does not understand, so I would like to ask if this is normal or if the HW design is incorrect.
Additionally, if you have any advice or references regarding HW design, please ask.

The document referenced by HW was TIDRW71A-EVM.pdf.

  • 0
    TI__Genius 10870 points

    Hi JunChul,

    You're image of the hardware is a little unclear, but my understanding is that you have only connected the UART TX and RX pins to a logic analyzer, and you are seeing the device sending out the data? 

    If this is the true, then it looks like you are experiencing an interesting case of what back-powering the device. It is possible to (incorrectly) power the device from pins that are not the power supply. This can lead to unexpected behavior such as code execution from unknown addresses, and can potentially damage your device. We do recommend that you do not apply a voltage to a pin that is higher than the voltage applied to Vdd to avoid unexpected behavior in the device. So I would recommend that you do not continue to do this.

    This is not necessarily indicative of a hardware design flaw. You should check that your hardware does not violate any of the specifications set in the datasheet. As long as you do follow the datasheet specifications, then you can anticipate the device to behave as specified in the datasheet, device family users guide, and errata sheet.

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