If the microcontroller’s (MCU’s) GPIO is configured to Quasi-High by default. When the MCU is powered on, the I/O will keep High until I/O mode or output logic is changed.

If the component outside the MCU needs to keep logical low, there may be problems with the transient logical high when the MCU is powered on. This problem can be figured by a pull-down resistor to keep the I/O in a logical low condition.

Notice that, when a pull-down resistor is added to the I/O, if the resistance is too large, the voltage may not be reduced; if the resistance is too small, the leakage current may increase.

To add a pull-down resistor in the application, a value of 1kΩ can be used in the NuMicro® family MCU to meet the need.

Products:	Microcontrollers ,8bit 8051 MCUs ,Arm Cortex-M0 MCUs ,Arm Cortex-M4 MCUs
Applications:
Function:	Peripherals,I/O,GPIO

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How many pull-down resistors are needed to keep I/O low when I/O power-on is initially configured to Quasi-High? Issue Date：2018-03-08

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