IR remote control transmitter application note (PDF!) from Microchip:
This application note illustrates the use of the PIC10F206 to implement a two-button infrared remote controller. The PIC10F2XX family of microcontrollers is currently the smallest in the world, and their compact sizes and low cost make them preferable for small applications such as this one.
Two example protocols are shown. The first is Philips® RC5, and the second is Sony™ SIRC. These two protocols were chosen because they are fairly common and their formats are well documented on professional and hobbyists’ web sites. They also demonstrate two differing schemes for formatting the transmission.