But weak vs strong does apply in the practical matter of Current Consumption. In your button scenario, the time it takes to switch from one state to the other isn't important, so weak vs strong doesn't apply there. They are completely relative to your needs, not just other pull resistors like internal ones. weak is usually clarifying which of these concerns (or perhaps others) are more important for a particular application.Ī "weak" pull resistor is usually a high value resistor that only allows a small amount of current through, and can quickly be overwritten, but takes longer to reassert itself.Ī "strong" pull resistor is usually a low value resistor, allows more current through, takes longer to be overwritten, but can quickly reassert a line. Of course, you usually want all of these things, but a resistor can't be both. Batteries will thus last longer, parts can be smaller and don't get as hot. (Think about Ohm's law)Ī weak or high resistance pull-up/down resistor is good because it will not require much current from the driving circuitry to work against the resistor. The reference for this relationship must be inferred from context.Ī strong or low resistance pull-up/down resistor is good because the time constant formed the load capacitance (often, the input gate capacitance, and the PCB trace capacitance) is small, so rise/fall times will be short.Ī strong pull-up/down resistor is good because noise currents from unintended coupling and EMI will result in smaller noise voltages. Of course low and high are relative terms, and so are strong and weak. Sometimes, a specific pull-up/pull-down resistor value required which necessitates using an external pull-up/pull-down instead of a chip’s internal pull-up/pull-down.Strong means low resistance. Many microcontrollers supply internal pull-up/pull-down configuration options. So, the remaining GPIO pins are reluctant to voltage fluctuations which may lead to the leakage of the current. Please note that it’s always safe to keep unused GPIO pins in one of the states. GPIO configuration resistors are GPIOx_MODER, GPIOx_OTYPER, GPIOx_OSPEEDR, and GPIOx_PUPDR. There is configuration resistor for every GPIO port which enables us to handle internal pull-up /pull-down resistor. Let’s see how to activate the internal pull-up/pull-down resistor. In Figure 2 internal pull-down resistor is activated, which drives pin to the ground. In Figure 1 internal pull-up resistor is enabled, which drives pin to high voltage. It’s a simple circuit in which the floating state is avoided by introducing or activating internal pull-up /pull-down resistor. Let’s understand the GPIO pin in input mode with external or internal pull-up/pull-down resistor connected, as shown in Figure 1 and Figure 2.
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