Verification error uploading sketch - but code writes just fine

I have a bunch of Arduino pro mini boards. Programming is via a cheap FTDI breakout board with "deek-robot" written on the back. The desktop machine is a mac running MacOs Sierra. The Arduino IDE is V1.8.5.

Using the FTDI board for serial comms works fine even at high speed (1Mbit). This board will write sketches to the Pro Mini just fine. The data all gets there and the downloaded code runs perfectly. I have no concerns that the write phase works.

However, the verification phase gives me:

avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0342
         0x3f != 0x1f
avrdude: verification error; content mismatch

avrdude done.  Thank you.

the selected serial port 
 does not exist or your board is not connected

The location of the mismatch is not constant but there always is one.

Other FTDI breakout cables work fine.

After six hours or so of searching through Google, messing with different FTDI breakouts, reloading bootloaders, remaking cables and so on, I am now sure it is this one FTDI breakout board. The chip on it is a FT232R1 and gets reported with a proper Vendor ID so I guess it is genuine.

Since it writes the code well enough, I am inclined to just ignore the errors, replace the FTDI board and move on.

But I really would like to know if anyone have seen similar behaviour and/or knows what might be going on.

Hi peterharrison

Yes! I have just had exactly the same issue.

My first venture into Pro Mini + FTDI with a simple LED flash sketch and at one stage at the end of the upload I got
'the selected serial port
does not exist or your board is not connected' (the same layout as you)
AND the sketch worked (it was different to the pre-loaded sketch)

BUT there were a number of other issues like:

  • First it would not upload on COM12
  • Then TWO ports appeared - COM12 and COM16. Selecting COM16 it uploaded correctly but brought up the above error!
    But then the FTDI USB socket developed a fault (loss of power) so until I can fix that I can't investigate further and start a new thread, but I just thought I would say I had seen it too.

BTW applying power to 5v & GND on the 'dead' FTDI brings up the LEDs on it and the Pro Mini, and the sketch runs ok, so I have something to work on.

My Pro Mini has Processor: ATmega 328P(5v, 16MHz)
I am on Win10 and my Arduino IDE is V1.8.9

This post is just a holding post as peterharrison never responded - he seems to have vanished!

I never managed to fix the fault with that FTDI (my first) - the USB socket turned out to be faulty.

My second FTDI brought up the dreaded ‘USB device not recognised’ error (see attachment) - otherwise known as ‘The revenge of the genuine manufacturer against the cheap clones’. There are plenty of solutions to that, the clearest being: and the link to FTDI Driver Fix.txt - if only Win10 would allow me to edit ftdibus.inf with my Administrator privileges!

Now on my third FTDI (this time from one of my regular suppliers) I can upload to a Pro Mini OK but get the error: the selected serial port does not exist or your board is not connected (and associated protocol errors).
Despite this the code works fine as does the Serial Monitor - which is where this all began!!!

So now begins another time wasting search through the solutions (of which there are many).

I really am beginning to regret trying out Pro Minis with FTDI - Nanos are so much simpler, and well worth the small increase in price - to say nothing of the massive amount of time I would have saved!

USB device not recognized.jpg