Datasheet

program.

If you crash your user program, or have a program that halts or otherwise fails, the user com port can disappear.

When the user COM port disappears, Arduino will not be able to automatically start the bootloader and upload

new software.

So you will need to help it by performing the click-during upload procedure to re-start the bootloader, and upload

something that is known working like "Blink"

I don't understand why the COM port disappears, this does not happen on my Arduino UNO!

UNO-type Arduinos have a

seperate

serial port chip (aka "FTDI chip" or "Prolific PL2303" etc etc) which handles all

serial port capability seperately than the main chip. This way if the main chip fails, you can always use the COM port.

M0 and 32u4-based Arduinos do not have a seperate chip, instead the main processor performs this task for you. It

allows for a lower cost, higher power setup...but requires a little more effort since you will need to 'kick' into the

bootloader manually once in a while

I'm trying to upload to my 32u4, getting "avrdude: butterfly_recv(): programmer is not responding" errors

This is likely because the bootloader is not kicking in and you are accidentally trying to upload to the wrong COM

port

The best solution is what is detailed above: manually upload Blink or a similar working sketch by hand by manually

launching the bootloader

I'm trying to upload to my Metro M0, and I get this error "Connecting to programmer: .avrdude: butterfly_recv():

programmer is not responding"

You probably don't have Metro M0 selected in the boards drop-down. Make sure you selected Metro M0.

I'm trying to upload to my Metro and i get this error "avrdude: ser_recv(): programmer is not responding"

You probably don't have Metro M0 selected in the boards drop-down. Make sure you selected Metro M0