V-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.
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 18 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.
You can choose the License: Open Source or commercial. Click here for details.
This diagram shows a typical circuit for a bus powered device.
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.