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AM6442: AM6442: Impact of Boot Mode Pin Pull Resistors on UART and GPIO Operation Post Boot

Siva M
Prodigy 60 points
Part Number: AM6442

Tool/software:

Hi Team,

I’m using the AM6442BSFFHAALV processor in my design. I’ve configured all 16 boot mode pins with external pull-up or pull-down resistors, and I’m reusing these pins as UART or GPIO after boot.

Here are the implementation details and queries

Boot Pin Configuration:

  • Some boot pins have fixed 10kΩ pull-up or pull-down resistors.

  • Some pins have DIP switch-controlled 499Ω pull-up + 49.9kΩ pull-down combinations.

  • After booting, the same pins are used as UART (TX/RX) or GPIO (Input/Output).

Post-Boot Usage Summary:

Boot Mode Pin Pull Resistors Post-Boot Function Interface
BOOTMODE0 10kΩ PU (fixed) UART2 RX UART
BOOTMODE1 10kΩ PU (fixed) UART2 TX UART
BOOTMODE2 10kΩ PD (fixed) GPIO Output GPIO
BOOTMODE3 499Ω PU + 49.9kΩ PD via DIP switch UART3 RX UART
BOOTMODE4 499Ω PU + 49.9kΩ PD via DIP switch UART3 TX UART
BOOTMODE5 499Ω PU + 49.9kΩ PD via DIP switch GPIO Output GPIO
BOOTMODE6 10kΩ PU (fixed) UART4 RX UART
BOOTMODE7 10kΩ PD (fixed) UART4 TX UART
BOOTMODE8 10kΩ PD (fixed) GPIO Output GPIO
BOOTMODE9 499Ω PU + 49.9kΩ PD via DIP switch GPIO Input GPIO
BOOTMODE10 10kΩ PU (fixed) GPIO Input GPIO
BOOTMODE11 10kΩ PD (fixed) GPIO Input GPIO
BOOTMODE12 10kΩ PU (fixed) GPIO Output GPIO
BOOTMODE13 499Ω PU + 49.9kΩ PD via DIP switch GPIO Input GPIO
BOOTMODE14 10kΩ PD (fixed) UART6 RX UART
BOOTMODE15 10kΩ PD (fixed) UART6 TX UART

Queries:

  • Will these pull resistor values affect UART signal quality or cause any issues during data transmission?

  • Will GPIOs toggle properly between 0 V and 3.3 V, or will the resistors cause weak logic levels?

  • Any general TI guidelines or best practices on using boot pins for I/O after boot?

  • 0
    TI__Mastermind 20476 points

    Hello,

    The concerned expert is out of office till June 14th. Please expect a delay in response.

    Regards,

    Nihar Potturu.

  • 0 in reply to Nihar Potturu
    TI__Expert 5525 points

    Greetings,

    As Nihar stated, our expert is out of office but may be potentially out longer than June 14th. Please expect a possible further extended amount of time before a response.

    Sincerely,

    Lucas

  • 0 in reply to Lucas Bowe
    TI__Guru* 86550 points

    In order to determine proper pullup/down resistor values, you have to consider the worst case combination of all internal leakage paths of all devices connected to the particular signal.  The external resistor should be sized to ensure that the signal goes higher than the min Vih for high signals, or less than Vil for low signal.  

    Also, if you are intending to use a boot signal for some other purpose after boot, you have to ensure the peripheral that is attached does not conflict with the boot mode pulls around the time PORz_OUT goes high (this is when the boot pins are latched).  You would have to do this with either an external buffer or ensure the peripheral is not driving signals at the boot latching time.

    Regards,

    James