I ran the following code to output a high signal from an Arduino UNO R4 IO port, but instead it output a low signal. digitalWrite(D10, HIGH); pinMode(D10,OUTPUT); Executing "digitalWrite(D10, HIGH)" again output a high signal, but now it outputs a low signal for just a moment. Is there a solution…

Attach an external pull-up resistor, eg. 10K? I think that will also produce a short low pulse... What external circuit is the pin connected to?

A discussion on the subject: [image] Nano R4 GPIO switching Nano R4 I wonder whether anyone else has noticed this issue with the Renesas RA4M1 GPIO switching? In my code, the GPIO is held high with INPUT_PULLUP when in idle state. When I need to send something…

D10 is connected to VDD via a resistor (1.5kΩ) and an LED. I see a similar issue has already been discussed. Thank you for the reference. It seems that pinMode() needs to be modified to fundamentally solve this problem.

[image] arduino_renetaro: digitalWrite(D10, HIGH); pinMode(D10,OUTPUT); Should piMode() function be written before digitalWrite() function?

[image] arduino_renetaro: D10 is connected to VDD via a resistor (1.5kΩ) and an LED. Does the LED flash visibly when the low pulse occurs? It should be very brief indeed, barely noticeable to the eye. Why is that a problem? Why not connect the pin to ground via the resistor and LED? Then the…

In this case, if I'm only controlling an LED, LOW pulse won't be much of a problem. However, if we were to use it for communications or CMOS control, LOW pulse would be unacceptable. Just to be safe, I've written an example of an improved pinMode(). I've only tested it with output, but I hope it …

[image] GolamMostafa: Should piMode() function be written before digitalWrite() function? Not necessarily. On AVR processors it enables the internal pull-up so the signal is high and when switching to output the pin will stay high. If you first do the pinMode the output will go low at the mo…

IO port output problem in Arduino UNO R4

Official Hardware UNO Family UNO R4 Minima

GolamMostafa January 6, 2026, 9:33am 6

Should piMode() function be written before digitalWrite() function?

Which order to follow: pinMode()-digitalWrite() or digtalWrite()-pinMode() to assert HIGH (VOH) on a DPin?

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IO port output problem in Arduino UNO R4

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