I have an Arduino Leonardo that I am using to emulate a Keyboard using the keyboard.press function with the Keyboard.h libraries. I have gotten the Keyboard.press function to work on my windows and mac- the keystroke I used was CTRL N to test- this worked well. So my ultimate goal was to emulate a keystroke ,F1, on a PC that is not running an OS- meaning I want the sketch to run in BIOS. for context, This keystroke (F1) tells the computer to use the a bootable USB to run a certain MathWorks OS. The problem, when it is plugged in the Arduino shows that power is receieved by lighting the POWER LED but it does not begin the sketch. The RED LED that usually flashes ( TX or RX im not sure) when it is running a sketch is not happening (not illuminating). How can I troubleshoot this and what could be happening? I have read that maybe too much serial info is going to the board so it confuses the board and does not begin the sketch.

I appreciate all the following help!!

  • When you have booted into Windows or OSX, how long does it take from the moment you plug the Leonardo into the computer to the keystroke happening? Are you sure that the computer isn't leaving BIOS or POST before the Arduino has had a chance to boot itself? Feb 25, 2016 at 19:24

2 Answers 2


Because the computer doesn't have a full OS at POST time any USB keyboards attached to the system have to operate in a special "Boot Keyboard" mode.

Keyboards that implement the USB Boot Keyboard profile specified in the USB Device Class Definition for Human Interface Devices (HID) v1.11 and are explicitly configured to use the boot protocol will interrupt the CPU every time the keyboard is polled even if there is no change in state unless the USB controller overrides this behavior, and are limited to 6-key rollover (6KRO). This profile is intended to allow the BIOS to handle a USB keyboard in the absence of a USB-aware operating system. The recommended profile for keyboards that are not in boot mode in this specification limits keyboards to 6KRO and causes them to respond to an interrupt with a status report at least every half second even if there is no state change in the keyboard unless the USB controller overrides this behavior in order to implement typematic (the function that causes keys to repeat when they are held long enough). However, keyboards in non-boot mode are free to implement an alternative HID profile.

-- Wikipedia

Since it was not expected that anyone would be using the Leonardo to operate in the BIOS that functionality has never been implemented. The choice was to implement the entire system, which would have left less room for your sketch, or to just implement the parts that the majority of people would find useful (that is keyboard, mouse, joystick, etc) and leave out the extra stuff, leaving as much room for sketches as possible.

They chose the latter, since as I am sure you are well aware: "The needs of the many outweigh the needs of the one".

For your rather specific case it may be easiest to butcher an old USB keyboard and work out which pair of inputs to the matrix, when connected together, perform the function you require and design some small interface circuit to allow the Arduino to trigger that function.


Thanks for the Input, you were quite right Majenko. The keyboard.press does not work in BIOS. The problem has been solved by a patch ( I'm not sure if that's the correct terminology) I found on github. By a Nicohood, here is the project if anyone find this having the same issues as me.https://github.com/NicoHood/HID?files=1

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