I have several Pro Micro clones.

This morning I uploaded a sketch into one of them (that was previously unprogrammed, so it stayed in Bootloader mode) and when I wanted to upload the sketch a second time, the problem began:

When I now run the reset procedure for Arduinos with integrated USB (open the COM port of the Pro Micro for example in PuTTY at 1200 bps and close it again), the LEDs start flashing rapidly and the Arduino disappears from the Windows Device Manager.

Hover for a (slightly annoying) image:

LEDs flashing

So then I grabbed a second, identical Pro Micro and uploaded the Blink sketch into it. It was also previously unprogrammed. The sketch executed, but when I now do the reset procedure, it exhibits the same behavior now (flashing LEDs).

I can still upload sketches just fine, by setting the COM port to a different (arbitrary) COM port to prevent the reset procedure from reaching the Pro Micro and resetting the Pro Micro manually after starting the upload procedure.

This only happens with the 3.3V/8 MHz variant, not with the 5V/16 MHz variant. I have selected the appropriate variant in the IDE.

How can I repair the automatic reset function?

  • It's not really clear what you're asking. If you open and close the CDC @1200 baud, it will reset to receive new firmware over USB. This is what the Arduino IDE uses to upload new sketches. Link 1 Link 2 What are you trying to do? Why do you need to open it at a baud rate of 1200 baud? – tttapa Dec 2 '17 at 16:03
  • That's the point - it should reset and go to bootloader mode but instead it starts flashing and disappears completely from the device manager. – AndreKR Dec 2 '17 at 17:27

Arduino Pro micro will enter bootloader if you connect it with 1200 baudrate. See this pos Upload code on Arduino Leonardo using command line

  • I like your other post. Maybe you could expand this post a little, as it is a little short and terse. – Greenonline Jul 11 '18 at 7:32
  • And it doesn't answer the question. The question is about why it does not enter the bootloader. (The bootloader would be visible on the USB bus.) – AndreKR Jul 11 '18 at 9:01
  • @vanbwodonk, AndreKR will not receive a notification in his inbox and may see your reply, if you don't address your comment to him using an@ as I have just done to you. Repost your comment and add their name with the preceding @ – Greenonline Jul 11 '18 at 11:51
  • @AndreKR Actually i not really understand what are you asking about. Led flashing indicate that's Arduino Pro Micro successfully jump into bootloader. Of course it will change COM port under windows (I assume you using windows). – vanbwodonk Jul 12 '18 at 4:58
  • @vanbwodonk Are you sure that it should flash when in bootloader mode? Because mine doesn't, so this might indicate something. Can you make a video of the flashing and the device manager/lsusb so I can see the timing? – AndreKR Jul 12 '18 at 6:40

I was finally able to solve this by using one of the Pro Micros to re-burn the bootloader of the other one.

For reference, the process is like this:

  1. Change arduinoasisp.protocol=stk500v1 to arduinoasisp.protocol=arduino in %LocalAppData%\Arduino15\packages\arduino\hardware\avr\1.6.21\programmers.txt
  2. Connect the two Pro Micros like this: Programmer (on USB) Target GND ----------------- GND VCC ----------------- VCC 15 ------------------ 15 14 ------------------ 14 16 ------------------ 16 10 ------------------ RST

  3. Flash the example sketch "ArduinoISP" into the first Pro Micro

  4. Click "Burn Bootloader"

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