Multiple USB CDC interfaces in one PIC24

[Moe24]

Hello everybody,
I'm working with a PIC24FJ512GB606 and CCS compiler V5.115.
I'm trying to implement two USB CDC interfaces in the microcontroller.
Unfortunately I just find examples of CCS multiple HID interfaces.
I already spent a morning for modifying the CDC descriptor without any luck.

I believe more and more that the CCS library cannot handle two CDC interfaces. Is there someone how got this working?

[Ttelmah]

I have done this years ago, with the CCS library. It can be made to work.
However assuming you are using Windows, usbser.sys, is limited to
supporting a single serial device from a single USB interface. To get
multiple you have to use a replacement for this (I used a third party
interface, cannot remember where I got it), or it worked well from
Linux. I think the replacement driver I used was from FTDI.
So if you have your descriptors set up correctly, the issue is not the
CCS end, but Windows....
Devices offering multiple com ports use their own replacement for
usbser.sys

[Moe24]

Thanks for your answer. I will give it another try, when I have time at work.

[temtronic]

I've always thought of USB as an interface between TWO devices( say PC and mouse) and wonder just how much code is required to have a PC correctly communicate with two mouses ( mice ) on the same USB wires.
Maybe this dinosaur is missing something in what the 'project' is ?

[Ttelmah]

CDC (so normally serial), rather than Mice. Multiple serial ports are not a
lot of work especially on a PIC24.

[bkamen]

[Ttelmah]

Yes, _BUT_, it can't be done using the standard Windows ubser.sys CDC
driver. This is limited to one port per USB device.
This is why third party units giving multiple ports use their own drivers
for this. There are a couple built into the standard Windows driver 'set'.
I used an FTDI VID/PID pair (very much not allowed), and this then
allowed the use of the FTDI driver. OK for a one-off 'home' device, but
illegal if you wanted to sell the device, If you wanted to make such a device
for commercial use, you would either have to write your own driver, or
make an agreement to an existing driver supplier.
I had proved to myself that it was the Windows driver that was causing
the problem, by trying the device on Linus, where it worked fine.

[Ttelmah]

Done a look back at my notes, and I had to set the device up as
'Miscellaneous', not as a standard COM port. Device class 0xEF.

This is how I had to do it:
[url]
https://stackoverflow.com/questions/5508304/usb-communications-device-with-multiple-serial-ports-working-on-all-platforms
[/url]

[bkamen]

[Ttelmah]

In Linux it is relatively easy. You don't make a composite device. You just
make it a communications class device, with two instances.
That worked straight away for me in Linux.
That is the bottom bit in the post I pointed to.

The example for this are the multihid ones. Except you generate two
communication devices.

[bkamen]

[MJ]

I had the same issue in Windows and, in the end, opted for one USB and a CP2102 to the serial port, both running CDC. If cost is an issue, then you can use the cheaper WCH USB-Serial parts, but you can run into issues with older Win OS. Also, consider using a 16F145X running CDC, and you can then buffer and transfer using other methods.