Programming Arduino
Loading Arduino bootloader
It is possible to use the AVRISP program for Arduino to act as a programmer, in order to load the bootloader program onto an Atmel AVR micro-controller. An intermediary Arduino takes serial communications from a computer and sends to the target micro-controller the necessary signals via SPI pins and a reset pin.
Uploading sketches
Arduino boards with built-in USB-to-TTL serial converters are easy to program. One just selects the corresponding serial port in the "Tools>>Serial Port" menu item, preferring "tty." over "cu." in Mac/*nix systems.
Arduino boards without USB, such as the Mini Arduino Pro, include pins to attach to ground, TX, RX and DTR pins of a serial port or USB-to-TTL adapter. USB-to-TTL adapters may also supply the working voltage.
Breadboard Arduinos, in other words, Arduinos made by hand around an AVR micro-controller with a bootloader, may be programmed by connecting their TX, RX, and reset pins to the RX, TX, and DTR pins of a serial port.[1]
One can also use an Arduino as a USB-to-TTL adapter if the AVR micro-controller is removable, as in the Arduino Uno.[2]
