Cannot upload sketch on selfmade board

Hi everyone,

I am developing a software on a self made board with a ATMEGA2560. The communication is TTL (RXD0&TXD0) and RS232 ( The signal is also sended to a MAX3232ECDR(TX pin 11 and RX pin 12 of the MAX3232) and after to the RS232 port).

I burned the bootload using ICSP communication and an arduino uno with success but I am not able to upload sketchs on it.

The question :

I saw that RX and TX signals were sending 5V continuous. I wanted to know if wiring RX and TX to both TTL and the MAX3232 could be the issue here.

Otherwise even though I already checked, It might be a short on both or on the MAX3232.

Thanks in advance!

Post your schematic.

How are you resetting the board to start the bootloader?

On official boards, the DTR pin of the serial adapter is coupled to the reset pin by a 0.1uF capacitor. You've mentioned only RX and TX (and hopefully ground....)

A TTL serial signal is +5v when idle, so that sounds right.

Ok, i cutted the tracks between the MAX3232 and TTL and now it is working just fine. The issue is that my RS232 communication has become useless.
I attached the schematic to this message.

Obviously wiring both to the same communication port was not a good idea. I wired the MAX3232 to the communication port 1 instead of the 0.

...schematics of your board, is there USB/serial for uploading also?
If yes:
Usual problem with uploading is if there is something connected on Rx,Tx pins due to impedance mismatch.
The solution could be to add switch on the RS232 side which could disconnect TTL from MAX3232.
It could be realized by two transistors driven by signal, let say RTS. DTR and RTS acts the same way - avrdude feature - reset pulse at the begining of upload process. DTR is needed for RESET (more common). Simple modification in the avrdude you can keep RTS high during whole uploading process which will keep the transistors in OFF state.
I am using this in my devices.