The Sony Unilink protocol is usually meant to control the CD-player of an automobile and can also perform other various tasks. The Sony Unilink protocol can be used to connect other auxiliary devices to your car stereo (these devices vary from CD shuttles to iPods).
This project is an AVR Sony Unilink interface based on the Atmel ATmega8 microcontroller. The MCU runs at 7,3728MHz and the communication with the Unilink bus is made through Serial Peripheral Interface (SPI) and the software supports RS232 input and output. The source code was written in C and the files as well as schematics are available for download under GNU General Public License in the link below.
(Another Unilink interface project entitled GNUnilink, based on the PIC16F628 running at 10MHz is also presented under GNU License).
Atmel based Sony Unilink: [Link]