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CC2540 - Question about difference between high drive and standard GPIO

Seth Berggren
Intellectual 910 points

Other Parts Discussed in Thread: CC2540

Hello,

For the CC2540, P1.0 and P1.1 are high-drive capable (20 mA) and they do not have pullup/pulldown resistors. Are these two differences the only differences between these pins and the other GPIO pins? I ask because I am making low power mode considerations for running the CC2540 off of coin a cell battery.

When the device loses power (except for the battery), all of the pins are configured as inputs with pull-down resistor. In order to maximize the power savings, then, I should tie down P1.0 and P1.1 with external pulldown resistors, right?

Thanks,

Seth

  • 0
    TI__Guru 56590 points

    Hello Seth,

    You are correct if you have routed P1.0 and P1.1 out on the PCB. If they are unconnected you can simply set them to a defined level as outputs. If you use them as output to drive LEDs for example you should also be OK by just keeping them as outputs. During reset all GPIOS are configured as input.

    From the user guide which i guess you already read :)= :

    7.1 Unused I/O Pins
    Unused I/O pins should have a defined level and not be left floating. One way to do this is to leave the pin
    unconnected and configure the pin as a general-purpose I/O input with pullup resistor. This is also the
    state of all pins during and after reset (except P1.0 and P1.1, which do not have pullup/pulldown
    capability). Alternatively, the pin can be configured as a general-purpose I/O output. In either case, the pin
    should not be connected directly to VDD or GND, in order to avoid excessive power consumption.

  • 0 in reply to Eirik V
    Intellectual 910 points

    Thanks Eirik, this answers my question! But I have one more question: Why is the default resistor direction pullup? Is there any advantage (in terms of power savings or any other reasons) to configuring inputs with pullup rather than pulldown?

    Thanks,

    Seth

  • 0 in reply to Seth Berggren
    TI__Guru 56590 points

    To be honest, I am not sure. The reset pin has a fixed 20k pullup, so it might have been a design decision to make thing less confusing. But there might be another reason I am not aware of.