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MSPM0L1304: MSPM0L1304 BSL UART TX contention with VREF+

Amit Halfi
Prodigy 90 points
Part Number: MSPM0L1304


Tool/software:

Hi,

In the part number MSPM0L1304SRTRR, pin 2 is by default the BootStrap Loader UART TX signal.

Before the MSPM0L1304 is programmed, when the pin operates as BSL UART TX, is it outputting a signal? (push pull or open drain).

Or, is it waiting for receiving the connection CMD on the UART RX line first?

Explanation:

I am burning a program using the SWD or I2C interfaces, not the UART.

I would like to connect a voltage regulator to pin 2 to supply VREF+,

but if the MSPM0L is an output in this pin, then either the MSPM0L or the voltage regulator will be damaged.

The regulator does not wait for an Enable signal, it just works as soon as there is power supply.

Adding an analog switch to isolate between the regulator and the VREF+ pin is a viable solution, which I am trying to avoid because it increases BOM cost.

So, to summarize,

Is the BSL UART TX an output?

Thank you.

  • 0
    TI__Expert 5010 points

    Hi, 

    By default, only when you do the operation with RESET pin and BSL invoke pin (default is PA18) as shown in the figure below, then it will enter BSL and enable the corresponding UART or I2C pins. If you don't plan to do it when power on, the corresponding pins such as PIN 2, will not be used as BSL UART and you can use it as a normal pin.

    MSPM0 Bootloader (BSL) Implementation (Rev. C)

    Best Regards,
    Peter

  • 0 in reply to Peter Jiang
    Prodigy 90 points

    Thank you, Peter.

    As stated in the Bootloader user guide:

    Therefore, it seems the BSL is always invoked in the first power up of the device, when it sees it is not programmed.

    So this pin will immediately be an output upon first power up, and also every time the BSL is invoked.

    Is my understanding correct?

    If not, please advise how to avoid setting this pin as an output.

    Also, is this output high or low by default?

    If this output is low, then maybe I can make a work around in the VREF regulator implementation.

    Kind regards,

    Amit

  • 0 in reply to Amit Halfi
    TI__Expert 5010 points

    Hi,

    Amit Halfi said:
    So this pin will immediately be an output upon first power up, and also every time the BSL is invoked.

    The chip is shipped from the factory with a default pre-programmed BSL program, which includes the default configuration of the INVOKE pin and the communication method of the BSL, etc. so the chip will not automatically enter the BSL mode except you manually invoke it. From the MSPM0L1304_TRM, it describes as below.

    As it won't enter the BSL mode, it is treated as a normal digital I/O pin. According to the TRM, the default state of the I/O pin is high-impedance, and you can configure the pin state as you want after powering on.

    Best Regards,
    Peter