Riva, the bootloader used is detailed in my original post and in the reply #16. This last one is the one I'm using at this moment. Overall, I tried something like 3 or 4 different ones to try to solve this problem.

I tried your suggestion, but the 9.5 seconds delay is still there.

PavelK, if you've never changed the fuses settings on your Mega2560, I don't think there is a reason why you would do it now.

If you just want to solve the 10 sec issue, you wont solve anything by playing with the fuses settings.

PavelK, this exactly the same problem for me. I'm glad to know it's not a problem with my board   !

On my board, if I reset the board while serial monitor is open, it starts immediately. You can try.

Is this really necessary ? See the pictures, SNR > 200.

[problem]

Oh, you're right. Here is the corrected sentence:

I have inspected both signals with my oscilloscope and I didn't see anything problem there.

The signals were steady 5V.

I have inspected both signals with my oscilloscope and I didn't see anything there. If it's a problem of noise on the Rx with my setup, I think some people would have experienced the same problem with the Arduino Mega2560.

Maybe the bootloader is really waiting for something. But what and why ?

There are both high.

The question is why my circuit, although working as expected, is making the bootloader not working as it should ?

When I try that, there is no delay.

So, the problem must be with the bootloader, right ?

Here is the pic I took. The reset of the Mega2560 is on channel 1. When I open the serial monitor, it goes down from 5V to less than 1V and goes back to 5V within 3 ms.

I'm sending a part of my circuit schematic. It's almost exactly the same as of the Arduino Mega2560.

I tried something. I used SerialCallResponseASCII. I programmed it and opened the serial monitor. Within the delay (9,5 seconds), I've reset the chip by pulling the reset pin on my 3x2 headers to ground. The programmed started right away and the serial monitor began to show me data, as expected.

So I think there's a link between the request for a reset from the 16U2 and the 9,5 seconds delay.

You're right, I didn't install the one you asked me before sending the text file. For now, I installed this one :

https://github.com/arduino/Arduino-stk500v2-bootloader/blob/master/goodHexFiles/stk500boot_v2_mega2560.hex

The result is attached with this post.

For the 9,5 seconds, I first remarked it using « SerialCallResponse ». There was a 9,5 seconds between the opening of the serial monitor and the start of the program (and the reception of the first character). Now, I'm just using « Blink » since I can just watch the L LED (pin 13). If I plug the USB cable (or any other power source), the LED starts blinking right away, but when I start the serial monitor there's this 9,5 seconds delay.

I can do that !

Yes, 16,03 MHz (62.4 ns period).

Thank Nick for your help, it's greatly appreciated.

1.   I tried the CKOUT Fuse and watch the CLKO with my oscilloscope. Everything is normal, the clock is constant and always working. No problem there.

2.   There is absolutely no activity on either Rx/Tx pins except what I described before (which is happening in the firsts 15 ms).