atmega328 on a breadboard on arduino 1.8.5 not showing up

In case anyone assumes a problem here, this is the relevant section of my boards.txt (both the original section with bootloader and also the one I added, mostly to set the fuses differently - as mentioned above, both don't work, though):

Replacing the ATMEGA328P by a new one doesn't make any difference, either. Using a pull-up resistor (whether internal or 10k external) on the RX line doesn't make it work, either. If I add a blinking LED (ATMEGA328P pin 19), the LED is blinking as it is supposed to (indicating other pins and the clock are working fine and there are no hidden resets). With 1000 ms (as in the code) I can hardly get anything other than high. A delay(1) or delay(2) won't do much noticeable harm either, but already with 20 ms, I get a sporadic high for some time once in a while, and with 100 ms, there's almost exclusively high. Deleting the delay(1000) line, I get the correct signal on the TX pin (if I then connect a TTL2RS232 converter, it's even showing the correct output on a serial monitor). Using an oscilloscope on the ATMEGA328P pin 3 (TX), I see a high level all the time.

The code runs perfectly on an Arduino UNO, however, with the breadboard version, there is one problem. the loop function runs over and over again forever Minimal code example to illustrate my problem: Thus, I have no use for an Arduino bootloader and don't use it (although the problem also occurs if I flash the UNO or Duemilanove bootloader first and then upload my sketch). I have followed several guidelines and tutorials (mainly and ) to build an Arduino on Breadboard, that I'm exclusively programming via ISP. So, now, I'd like to ask more people who are more used to using AVRs without the Arduino board.

I've already posed this question in the Arduino forum last weeks, but it seems like - although I highly value that community, as well - nobody there has any idea how my problem can be solved. So already thank you for that! :) Now, I've come across a really weird problem using the Arduino IDE to program an ATMEGA328P on a breadboard. I've been reading on this forum for a while and it helped me on many problems with my design.

Atmega328 on a breadboard on arduino 1.8.5 not showing up