How To emulate a COMx port via USB using Microchip CDC Firmware

Start communicating with a PC.

Follow the Tutorial in a few steps:

Notice that most of these Steps are needed only for the 1st use !

Step 1: Requirements:
- have a USB devlopment board based on a PIC18F4550...
- have the device programmed with the USB boot firmware code,
- have already sucessfully used the USB Bootloader
That means you must follow the UsbBootload Tutorial before doing this one !
If you don't want to use the USB Bootloader, you must make some modifications in the CDC project (change the Linker Script file to a normal one, set all Conf Bits, export a complete hex file including Conf Bits...).

Step 2: Install needed softwares and get CDC Firmware Source Code
Microchip MPLAB 7.00+ available from http://www.microchip.com/ide/∞
Microchip C18 2.40+ available from http://www.microchip.com/c18/∞ (check all Config Options boxes when asked !)
Microchip CDC Firmware Source Code∞ ("CDC_RS232_Emulation.EXE∞")

Step 3: Adapt the firmware to your board
With a PICDEM FS-USB board (or complete clone), nothing to change, go to next step.
With a simplified clone (without SELF_POWER_SENSE_IO nor USB_BUS_SENSE_IO), edit the firmware:
Open MPLAB project :C:\MCHPFSUSB\fw\Cdc\MCHPUSB.mcp .
In usbcfg, comment both lines (start with //):
#define USE_SELF_POWER_SENSE_IO
#define USE_USB_BUS_SENSE_IO
Rebuild the project. This will update .\_output\MCHPUSB.hex.
If you use another Full Speed USB PIC (like 2455), also think to select your Device & replace the Linker Scripts file.

Step 4: Bootload the CDC firmware in the PIC
Connect the USB cable. It powers the PIC (not visible at this time).
Enter Boot Mode by pressing [S1 Reset] while maintaining [S2 enter Boot].
Bootload the HEX firmware file located at:
C:\MCHPFSUSB\fw\Cdc\_output\MCHPUSB.hex

Step 5: 1st CDC detection
Restart the board in user mode (reset while not pressing [S2 enter Boot]).
Normally, Windows will start detecting a new USB unknow device.

Step 6: Manualy specify "Microchip CDC" INF driver to MSWindows
At this point, you must have a window asking a driver for the new USB device.
The procedure depends on your Operating System version.
Don't let Windows find automatically a driver, or you will have to suppress the bad driver fille manualy!
Specify the driver location : C:\MCHPFSUSB\fw\Cdc\inf\win2k_winxp (mchpcdc.inf)
Now it should be recognised as "Communications Port" (COMx, COM3 for ex.).
You can verify in Windows Device Manager.

Step 7: Hyperterminal communication
Run MSWindows Hyperterminal (or others like this one∞).
Start Menu:Programms/Accessories/Communications/HyperTerminal
Create a new connection on COM3 with 115200 bauds rate (this value comes from cdc.c).
In the Hyperterminal, click Connect (Call) !
Then (& only then), push S2.
It must print :
Microchip Technology Inc., 2004
PIC18F4550 Full-Speed USB - CDC RS-232 Emulation Demo
Close the connection in the Hyperterminal before unpluging USB (thus you can reconnect USB and reuse the same connection in Hyperterminal without having to close/restart it).

Next: Your own program
To go further, try to do the examples proposed in user.c .
See Microchip documentation : AN956 Migrating Applications to USB from RS-232 UART∞
Then, you can start writing your own PC Comm application.