I've been trying to write a sketch that continously sends a character and the current micros() value until it gets a Serial input. I want to use it to test Serial communication between two Arduino-boards. One will Send and the other one will reply. However, I need to put some delay between the single transmissions, otherwise I won't be able to see if the last character sent is the one the other board replied to. But if I use the delay function, data received via Serial will not be displayed, when it arrives, but when the loop has finished its next circle. I couldn't find out how to fix this Problem (interrupts didn't work so far). I hope someone can help me.