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AM5728: UART unused pins

Hideaki Matsumoto
Genius 9805 points

Part Number: AM5728

Hi,

 

The customer is now development their own board with AM5728.

Could you tell them how they should treat unused pins of enabled UART3 ? It is used with RS232C transceiver device in development stage only. RS232C device will be removed for production, but software will be left, won’t be changed so UART3 will be enabled.

How should they treat the following pins ? What is value of ohm if pull-up/down register is needed ? I think TX can be left as open and some input pins like RX need pull register.

 

C26        gpio7_23

E23        gpio7_24

D28        uart3_ctsn

D26        uart3_rtsn

D27        uart3_rxd

C28        uart3_txd

 

Regards,

Hideaki

  • 0
    TI__Guru**** 393215 points

    Hi,

    Follow the guidelines in section 2.5 of www.ti.com/lit/an/sprack7b/sprack7b.pdf

  • 0 in reply to Biser Gatchev-XID
    TI__Genius 9805 points

    Sorry, this has not yet been resolved.

    We had already checked the schematic check list. The document describes as below, but their software enable UART3 as mentioned above. In this case, could you tell them how to treat unused pins of UART3 which is enabled ?

    2.5 Unused Signals
    Signals on interfaces that are unused can typically be left as no connect. Many of the IOs have a Pad
    Configuration Register that provides control over the input capabilities of the I/O (INPUTENABLE field in
    each conf_<module>_<pin> register). For more information, see the Control Module chapter of the devicespecific
    TRM. Software should disable the RX buffers that are no connects (INPUTENABLE=0) as soon
    as possible during initialization. This INPUTENABLE field defaults to "input active" for most signals, which
    means there is a potential for some leakage during powerup of the chip if the input floats to a mid-supply
    level before the software can initialize the I/O. This should only be a concern if you are attempting to
    power up the design with a minimum power consumption. Most designs should be able to tolerate this
    small amount of leakage in each floating I/O until the software has a chance to disable it. After disabling
    the receiver of the I/O, no leakage will occur.

    Thanks and regards,
    Hideaki

  • 0 in reply to Hideaki Matsumoto
    TI__Guru**** 393215 points

    Input pins should be pulled to inactive state. Output pins can be left open.