I use ATmega644P and need both UART. This modified loader use any 3 I/O line (RX, TX, LED) for load code from Arduino IDE. Test with ATmega644P (internal RC 8MHz), 38400 baud rates. PC5 = TX line, PC4 = RX line. LED on PB1. [+] Click to view code # include < inttypes.h > # include < avr/io.h > # include < avr/pgmspace.h > # include < avr/interrupt.h > # include < avr/wdt.h > # include < avr/boot.h > # ifdef ADABOOT # define START_LED_FLASHES 2 # define NUM_LED_FLASHES 3 # define ERROR_LED_FLASHES 5 # define ADABOOT_VER 1 # endif # ifndef BAUD_RATE # define BAUD_RATE...