AVR-CDC converts USB and RS-232C signals using the AVR micro- controller which has no on-chip USB interface. This technology is based on Object Deveopment's V-USB (Software-USB on AVR), and the CDC (Communication Device Class) protocol was extended over it. AVR-CDC enables PC to communicate with the USB device through virtual COM port.

The basic idea of using CDC protocol over Low-speed USB is based on Kyosuke Ishikawa's experiment in 2005. To make it stable and practical, Christian Starkjohann in Object Development helped me modifying his V-USB stack. Since three endpoints and the bulk transfer on low-speed device violates the USB standard, I added a tiny patch driver on Windows' USB stack.

Although this technology is quite experimental, it may be useful to interface your original system to PC easily. The circuit is very simple, but it requires a certain amount of skills to control. If you need practical or stable solutions, or you are not familiar with electronics nor installing drivers, use the dedicated chip from vendors like FTDI.

The back door to the low-speed bulk transfer is gradually closing on the newer OS. After enjoying this USB technology, switch to the HID protocol or to MCU having on-chip USB controller.

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2009/07/30  Renewal
2009/08/24  Windows 2000 driver fixed.
2010/02/06  CDC-SPI added.
2010/02/28  CDC-232 updated.
2011/06/24  CDC-232 updated.

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