AVR-USB implements a USB device entirely in software, making it possible to build USB hardware with almost any AVR microcontroller, not requiring any additional chip.
Features :
Features :
- Fully USB 1.1 compliant low-speed device, except handling of communication errors and electrical specifications.
 - Example projects demonstrate device and host driver implementations on Linux, Mac OS X and Windows.
 - Supports multiple endpoints: one control endpoint, two interrupt/bulk-in endpoints and up to 7 interrupt/bulk-out endpoints. (Bulk endpoints are forbidden for low speed devices by the USB standard.)
 - Transfer sizes up to 254 bytes by default, more as configuration option.
 - Comes with freely usable USB identifiers (Vendor-ID and Product-ID pairs).
 - Runs on any AVR microcontroller with at least 2 kB of Flash memory, 128 bytes RAM and a clock rate of at least 12 MHz.
 - No UART, timer, input capture unit or other special hardware is required (except one edge triggered interrupt).
 - Can be clocked with 12 Mhz, 15 MHz, 16 MHz or 20 MHz crystal or from a 16.5 MHz internal RC oscillator.
 - High level functionality is written in C and is well commented.
 - Only about 1200 to 1400 bytes code size.
 
