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MSP430F5509: the change about the ZHCS897G UART BSL

Part Number: MSP430F5509

Hello Team

Could you help explain why have this change? Detail please see following informationt.  Why apply a 1M resistor to ground?

  • Hello Xiao,

    I suspect ZHCS897G is not the correct name of the part you are referring to and that some additional information was not attached correctly. Please provide the correct part and resource you have a question about.

  • msp430f5509.pdfHello Ryan

    Thank you for your replay. Attached is the datasheet. In page 21,  The note describe that Applying a 1-MΩ resistor to ground is recommended. the question is that if  not apply this resistor, what will happen?

  • Hi Xiao,

    Thank you for clearing up this confusion. As stated in the datasheet, the PUR pin is used to invoke the default USB BSL on a logic high. Therefore a weak pull-down resistor should be applied to this pin to make sure that a floating condition does not falsely trigger the USB BSL. This information has nothing to do with the UART BSL mentioned in the post title and the PUR pin should be grounded if USB is not being used.