Hi Bill,
I did a similar project a while ago, used an ARM7 mcu with MAX3420 to
implement CDC class. I didn't need to do any host side programming. If
the MCU done the USB enumuration sucessfully, windows will find
the .sys file.
You don't need to do any USB-to-serial conversion on the host. If the
enumuration is sucessfull, you can send and receive data by opening
the appropriate COM port using a Terminal programme (HyperTerminal for
example).

Thanushan

Hi,

I want to exchange information between an AT91SAM7X256 and a PC
through USB. The MCU has the USB transceiver inside, and there is NO
USB-to-serial conversion involved, because the data is consumed inside
the MCU. There is no UART involved.

I don't want to write any code at the host side. At the most, editing
and using a ".inf" file. So, I 'm trying to take advantage of one of
the existing standard classes, like Communication Device Class (CDC),
and probably also the Abstract Control Model (ACM) within it.

Is there any driver, already installed in my PC as part of my Windows
XP, better suited for my need than "usbser.sys"? Is there any ".sys"
file in Windows that allows communication between the PC and a USB
device but without implying USB-to-serial conversion, and without
having having to deal, at the device, with functions that don't make
sense in this simpler application?

I was about to use that one, but the CDC requests SET_LINE_CODING and
SET_CONTROL_LINE_STATE would do nothing at the device side, and
GET_LINE_CODING would have to return information (about baud rate,
stop bits, parity, data bits) which tells nothing about the real
operation of the device.

Thank you,
Bill