Virtual USB port for AVR Microcontrollers

V-USB (formerly known as AVR-USB) is a software-only implementation of a low-speed USB device for Atmel’s AVR® microcontrollers, making it possible to build USB hardware with almost any AVR® microcontroller, not requiring any additional chip.

V-USB can be licensed freely under the GNU General Public License or alternatively under a commercial license. A comprehensive set of example projects demonstrates the wide range of possible applications.

Features of V-USB:

• 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. (Note that the USB specification forbids bulk endpoints for low speed devices, but V-USB supports them to some degree.)
• 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 12.8 MHz or 16.5 MHz internal RC oscillator.
• High level functionality is written in C and is well commented.
• Only about 1150 to 1400 bytes code size.
• Choice of licensing type: Open Source or commercial.

This diagram shows a typical circuit for a bus powered device using Atmel ATtiny2313 MCU...

D1 and D2 are a low cost replacement for a low drop 3.3 V regulator chip, such as the LE33. Operating the AVR at higher voltages exceeds the common mode range of many USB chips. If you need to run the AVR at 5 V, add 3.6 V zener diodes at D+ and D- to limit the voltage.

Download the V-USB package containing a short description and several simple code examples.