AVR-CDC


This is the Readme file to firmware-only CDC driver for Atmel AVR
microcontrollers. For more information please visit
http://www.recursion.jp/avrcdc/


SUMMARY
=======
The AVR-CDC performs the CDC (Communication Device Class) connection over
low-speed USB. It provides the virtual RS-232C interface without installing
dedicated driver. The AVR-CDC is originally developed by Osamu Tamura.
Akira Kitazawa has significantly contributed to improve this software.


SPECIFICATION
=============
AVR-CDC with USART (ATmega8, 48, 88..)
speed: 1200 - 19200bps
datasize: 5-8
parity: none/even/odd
stopbit: 1/2

AVR-CDC without USART (ATtiny45 and 85)
speed: 1200 - 4800bps
datasize: 8
parity: none
stopbit: 1
supply current: 8mA

Without USART, some characters will be corrupted if full-duplex transaction
continues long in high baud rate. Slower speed is recommended.

With USART, there are times when use of the receive interrupt causes
obstacle in USB communication. In that case, use polling version
(cdcmega*p.hex).

The actual transfer rate depends upon the terminal software strongly.
On Windows, HyperTerminal sends one character at a time for every packet.
Therefore, the transmission speed is one character/mSec at the maximum.

Although the CDC is supported by Windows XP/2000, Mac OS X,9.1, and Linux,
CDC on low-speed USB is not allowed by the USB standard. Use AVR-CDC at
your own risk.


USAGE
=====
Build your circuit and write firmware (cdcmega*p.hex/cdctiny*.hex) into it.
C1:104 means 0.1uF, R3:1K5 means 1.5K ohms.
High speed version is available on ATmega48-168. Recompile with
#define USE_UART_RXD_INTERRUPT in uart.h (cdcmega*i.hex).
If you use another bit for USB_CFG_DMINUS_BIT, modify usbconfig.h and
recompile codes. You can reverse the polarity of TXD and RXD if you need
connect to RS-232C directly on non-UART version (use cdctiny45r.hex).
Recompile with #define UART_CFG_INVERT 1 in uart.h.

If the connection is unstable, add another diode after D2.
Try other USB-Hub or PC, or make the maximum packet size smaller in main.c,
line 27.
#define HW_CDC_BULK_OUT_SIZE 7 or less

[Windows XP/2000]
When you connect with a USB port first, a Driver Setup Dialog appears.
Specify the folder in which "avrcdc.inf" exists, without searching
automatically. Although it is warned that the driver is not certified,
confirm it. It only loads Windows' built-in usbser.sys. Then, the Virtual
COM port appears.

[Mac OS X]
You'll see the device /dev/cu.usbmodem***.

[Linux]
The device will be /dev/ttyACM*.
Kernel 2.6 does not allow the low speed bulk transfer on UHCI host.
uhci_q.c / usb_uhci.c must be modified to enable bulk transfer.


DEVELOPMENT
===========
This driver has been developed on AVR Studio 4.13 SP2 and WinAVR 20071221.
If you couldn't invoke the project from cdc**.aps, create new GCC project
named "cdctiny" or "cdcmega" under "avrcdc/" without creating initial
file. Select each Makefile at "Configuration Options".

The code size of AVR-CDC is about 3KB, and 128B RAM is required at least.

Fuses to be checked
[RSTDISBL=1] (ATtiny only)
[WDTON=0]
[BODLEVEL=101]
[CKSEL=1110 SUT=11]
ext fuse
ATmega8 9F-FF
ATmega48/88 FF CE-FF
Disabling Reset pin requires the High Voltage Serial Programming at ATtiny.


USING AVR-CDC FOR FREE
======================
The AVR-CDC is published under an Open Source compliant license.
See the file "License.txt" for details.

You may use this driver in a form as it is. However, if you want to
distribute a system with your vendor name, modify these files and recompile
them;
1. Vendor String in usbconfig.h
2. COMPANY and MFGNAME strings in avrcdc.inf



Osamu Tamura @ Recursion Co., Ltd.
http://www.recursion.jp/avrcdc/
26 June 2006
7 April 2007
7 July 2007
27 January 2008