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MSP430F5342: MSP430 Booting issue

Nachiketh Karanth
Intellectual 840 points

Part Number: MSP430F5342

Hi Team,

I am using TXS series level translator for FPGA UART signals in my board. When i connect the UART cable (TTL-232R-3V3) and power ON the board, MSP430 does not boot. When further debugging, i found that due to TXS series level translator used for UART, voltage is getting back-driven to MSP pins. 

I do not have the option to replace this TXS with TXB series level translator nor can I isolate the signals connected to MSP430 that are back-driving voltage. 

Without MSP430 booting, my board will not get any power as MSP430 is used to control power regulators. So, initially i can't even keep the MSP430 in reset. Can i have any inputs on how this can be solved, is there anything that can be implemented in software or hardware?

Thanks

  • 0
    Guru 25825 points

    The short answer is that it would seem that you have violated the absolute maximum voltage specification of Vcc+ 0.3V. (Even when Vcc = 0V) Don't do that. It forward biases the clamping diode to Vcc. The MSP430 is very low power so it doesn't take much to pull Vcc up to a level where it can cause trouble.

    You have to do something to keep anything from driving the MSP430 pins high before it has power. Normally you would just worry about the RXD pin but since you are using a bidirectional translator, you have to worry about the TXD pin as well.

    For RXD, if it is compatible with the bit rate, a simple diode (so the TXS can pull the pin down) and pullup resistor to the MSP430 Vcc should work. For TXD you have make sure that the translator doesn't decide to drive that pin when the MPS430 is unpowered.

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