AVR272: USB CDC Demonstration UART to USB Bridge Features • • • • • Supported by Windows® 2000 or later No driver installation Virtual COM Port Enumeration USB to RS232 Bridge with dynamic baudrate Bus powered 8-bit Microcontrollers Application Note 1. Introduction The RS232 interface has disappeared from the new generation of PCs replaced by the USB interface. To follow this change, applications based on UART interface have to migrate to USB. Migration to USB can mean heavy development both on the PC and on the device side. To avoid this development, Atmel offers you a solution based on the CDC class (Communication Device Class) with the following advantages: No need to change the PC application Few modifications from the device side The aim of this document is to describe how to start and implement a CDC (Virtual COM Port and UART to USB bridge) application using the STK525 starter kit and FLIP in-system programming software. A familiarity with USB Software Library for AT90USBxxx Microcontrollers (Doc 7675, Included in the CD-ROM & Atmel website) and the CDC specification (http://www.usb.org) is assumed. Figure 1-1. Virtual COM Port Application Software based on RS232 Library USB interface 7619B–AVR–04/08 2. Hardware Requirements The USB CDC application requires the following hardware: 1. AVR USB evaluation board (STK525, AT90USBKey, STK526...or your own board) 2. AVR USB microcontroller 3. USB cable (Standard A to Mini B) 4. RS232 crossed Cable (DB9 male to DB9 female) 5. PC running on Windows® (2000, XP) with USB 1.1 or 2.0 host Note: An additional STK 52x and USB port are required if the PC has no RS232 interface. 3. In system programming and Device Firmware Upgrade To program the device you can use the following methods: • The JTAG interface using the JTAGICE MKII • The SPI interface using the AVRISP MKII • The USB interface thanks to the factory DFU bootloader and Flip software • The parallel programming using the STK500 or the STK600 Please refer to the hardware user guide of the board you are using (if you are using Atmel starter kit) to see how to program the device using these different methods. Please refer to Flip(1) help content to see how to install the USB driver and program the device through the USB interface. Note: 2 1. Flip is a software provided by atmel to allow the user to program the AVR USB devices through the USB interface (No external hardware required) thanks to the factory DFU bootloader. AVR272 7619B–AVR–04/08 AVR272 4. Quick Start Once your device is programmed with usb_cdc.a90 file, click on Start Application button on FLIP or push the reset button from the STK525 board to start the CDC demonstration. A new device detection wizard will appear, point the wizard to the inf folder included in the CDC package. Check that your device is enumerated as COM port (see Figure 4-1), then you can use the STK525 as a Virtual COM Port or USB to UART bridge. Figure 4-1. CDC enumeration 3 7619B–AVR–04/08 The figure below shows the STK525 used by the demo (you may use another kit: AT90USBKey, STK526, depending on the AVR USB product you are working with): Figure 4-2. STK525 R S 2 3 2 C o n n e c to r U S B C o n n e c to r J o y s t ic k 4 AVR272 7619B–AVR–04/08 AVR272 4.1 Virtual COM Port Demo The purpose of the Virtual COM Port demonstration is to communicate with a RS232 PC application without any software modification. Follow the instructions below to start the demo: 1. Lauch the HyperTerminal application and select the correct COM port as indicated in the device manager. Figure 4-3. COM Port selection 2. Press the joystick and you will see the selection or the direction status written on the HyperTerminal window. Figure 4-4. Virtual COM Port Demo 5 7619B–AVR–04/08 4.2 USB to UART Bridge The aim of the USB to UART bridge is to transfer data in full duplex mode between UART and USB interface. This application can be used to connect any RS232 device to a PC which does not have an RS232 interface. Follow the instructions hereunder to start the demo: 1. Connect the RS232 port of the STK 525 to The PC RS232 port. Note: If the PC has no RS232 interface you can use another STK525: Connect the two boards with a RS232 crossed cable and connect each board to a USB port on the PC. 2. Lauch two HyperTerminal applications (one with the RS232 port and the second with the Virtual COM port) with the same configuration (Baudrate, Data bits, Parity, Stop bits, Flow control). 3. Write something in one HyperTerminal, it will be displayed in the other. Figure 4-5. 6 USB to UART Bridge AVR272 7619B–AVR–04/08 AVR272 5. Application Overview The CDC application allows the user to simulate an RS232 port using the USB hardware. The device appears as a COM port instead of USB device in the device manager. This allows the user to use his RS232 application without changing his PC application. From the embedded side, the UART driver is replaced by the UART-USB Driver. The user has to use the UART-USB functions instead of the UART functions to communicate with the PC. Once the device has enumerated, the application ensures a full duplex data transfer between the PC and the peripheral. The figure below shows the structure: Figure 5-1. USB to UART migration PC Application PC Application UART API UART API CDC Drivers UART hardware USB hardware USB RS232 UART hardware USB hardware UART Driver UART- USB Driver Embedded Application Embedded Application 7 7619B–AVR–04/08 6. Firmware As explained in the USB Software Library for AT90USBxxx Microcontrollers, all USB firmware packages are based on the same architecture (please refer to this document for more details). Figure 6-1. USB CDC Firmware Architecture config.h CDC application management Start up main.c Enumeration management conf_scheduler.h usb_task.h cdc_task.c usb_task.c usb_standard_ request.c usb_specific_ request.c usb_standard_request.h usb_specific_request.h uart_usb_lib.c usb_descriptors.c usb_drv.c Drivers API HID application scheduler.c uart_usb_lib.h usb_descriptors.h conf_usb.h stk_525.c usb_drv.h Hardware cdc_task.h stk_525.h USB hardware interface Should not be modified by user Can be modified by user Added by user This section is dedicated to the CDC module only. The customization of the files described hereafter allow the user to build his own CDC Application. 8 AVR272 7619B–AVR–04/08 7619B–AVR–04/08 Send data trough USB UART<->USB USB<->UART ?? Fifo endpoint size = Send data trough UART ?? ?? Send data trough USB on USB UART Bridge USB-UART ?? !timeout && UART !=0 Data received on Figure 6-2. Joystic pressed Data received Data received on 6.1 Port Virtual Com Initialization AVR272 cdc_task.c This file contains the functions to initialize the hardware which will be used by the application, collect data and transfer it. CDC Application 9 6.1.1 cdc_task_init This function performs the initialization of the CDC parameters and hardware resources (joystick...). 6.1.2 cdc_task This function manages the data transfer for the two demonstrations (Virtual COM Port and UART to USB Bridge). 6.2 uart_usb_lib 6.2.1 uart_usb_test_hit This function checks if at least one character has been received on the USB. 6.2.2 uart_usb_getchar This function returns the byte received in the OUT endpoint FIFO. 6.2.3 uart_usb_putchar This function writes the byte put in parameter into the USB IN endpoint FIFO. It also replaces the putchar function of the UART library. For example the printf will be based on uart_usb_putchar fuction instead of putchar. 6.2.4 uart_usb_tx_ready This function checks if a byte can be written in the IN endpoint FIFO. 6.2.5 uart_usb_flush This function sends data stored in the IN endpoint. 6.3 stk_525.c. This file contains all the routines to manage the STK 525 board resources (joystick, potentiometer, temperature sensor, LEDs...). 7. PC Software The CDC application uses the native Windows drivers. It requires only an INF file located in the inf folder from the CDC package. 8. Limitations This application does not work with Windows 98 and ME (no native driver of CDC device). This application can work with Linux OS, but support depends on configuration. 9. Related Documentation • AVR USB Datasheet • USB Software Library for AT90USBxxx Microcontrollers • USB CDC class specification 10 AVR272 7619B–AVR–04/08 Headquarters International Atmel Corporation 2325 Orchard Parkway San Jose, CA 95131 USA Tel: 1(408) 441-0311 Fax: 1(408) 487-2600 Atmel Asia Room 1219 Chinachem Golden Plaza 77 Mody Road Tsimshatsui East Kowloon Hong Kong Tel: (852) 2721-9778 Fax: (852) 2722-1369 Atmel Europe Le Krebs 8, Rue Jean-Pierre Timbaud BP 309 78054 Saint-Quentin-enYvelines Cedex France Tel: (33) 1-30-60-70-00 Fax: (33) 1-30-60-71-11 Atmel Japan 9F, Tonetsu Shinkawa Bldg. 1-24-8 Shinkawa Chuo-ku, Tokyo 104-0033 Japan Tel: (81) 3-3523-3551 Fax: (81) 3-3523-7581 Technical Support [email protected] Sales Contact www.atmel.com/contacts Product Contact Web Site www.atmel.com Literature Requests www.atmel.com/literature Disclaimer: The information in this document is provided in connection with Atmel products. No license, express or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of Atmel products. EXCEPT AS SET FORTH IN ATMEL’S TERMS AND CONDITIONS OF SALE LOCATED ON ATMEL’S WEB SITE, ATMEL ASSUMES NO LIABILITY WHATSOEVER AND DISCLAIMS ANY EXPRESS, IMPLIED OR STATUTORY WARRANTY RELATING TO ITS PRODUCTS INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL ATMEL BE LIABLE FOR ANY DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE, SPECIAL OR INCIDENTAL DAMAGES (INCLUDING, WITHOUT LIMITATION, DAMAGES FOR LOSS OF PROFITS, BUSINESS INTERRUPTION, OR LOSS OF INFORMATION) ARISING OUT OF THE USE OR INABILITY TO USE THIS DOCUMENT, EVEN IF ATMEL HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Atmel makes no representations or warranties with respect to the accuracy or completeness of the contents of this document and reserves the right to make changes to specifications and product descriptions at any time without notice. Atmel does not make any commitment to update the information contained herein. Unless specifically provided otherwise, Atmel products are not suitable for, and shall not be used in, automotive applications. Atmel’s products are not intended, authorized, or warranted for use as components in applications intended to support or sustain life. © 2008 Atmel Corporation. All rights reserved. Atmel ®, logo and combinations thereof, and others are registered trademarks or trademarks of Atmel Corporation or its subsidiaries. Other terms and product names may be trademarks of others. 7619B–AVR–04/08