USB CDC support for PIC24FJ32GU205

[robleso7473]

Hello Everyone,

I am starting a new project where I want to use the PIC24FJ32GU205 to implement a USB CDC so I can send serial data from another device to the computer through this MCU. Does CCS have drivers/code to implement USB CDC functionality?

Thanks for your feedback,

O.

[Ttelmah]

Yes.
Standard driver with the compiler. usb_cdc.h
Assuming you have a modern compiler, the usb_serial example has been
rewritten to support the DS PIC's. About 2010, then some issues fixed
in 2013!....
Look at the usb_serial examples.

[robleso7473]

Hi Ttelmah,

I have the PCWHD version 5.116 (I have been compiling code for the PIC24FJ32GU205) so I think this is the modern version - correct?

Thanks for your response. I do see the driver and examples.

Has CCS tested the driver and examples on this newer device (PIC24FJ32GU205)? You mentioned some issues had been fixed in 2013 but I want to say the PIC24FJ32GU205 was released after that (correct me if I'm wrong).

Thank you again,
O.

[Ttelmah]

The basic USB stack doesn't change with chips. The problems were issues
with moving from the older chips.

[robleso7473]

Sounds good!
As always, great support.
Thank you.
O.

[Ttelmah]

As a comment, some remarks about USB in general.

Keep your connections on the board short, each close to the same length,
and make sure the track spacing is correct for the characteristic impedance.
For USB2, the connection length should not exceed 25mm.
Make sure you add detection for the connection being made.
The drivers on your chip meet the impedance spec. So no termination
required.

[robleso7473]

Hi Ttelmah,

I appreciate the additional recommendations. I am not totally familiar with the various USB connection standards but as I'm going to be bridging at most 1Mbaud serial data I would want to connect with Full Speed (12 Mb/s) USB. I suspect a signaling rate of 12 Mb/s should not require very strict differential pair (USB +D/-D) routing requirements. Maybe I'm wrong on that - what do you think?

I certainly do not plan on using USB2.0, as I read through the PIC24FJxxGU spec I don't see USB having USB2.0 capability. It does have what they call 'USB On-The-Go" but not sure that's higher than 12 Mb/s signaling rate.

thanks,
O.

[robleso7473]

I forgot to add one question: You mentioned that I should add detection. Is that a SW thing or is that an actual pin on the PIC24FJ32GU205 that needs to be connected to something?

The pinout on this device, regarding USB related connections, only has USBOEN_, Vbus, Vusb3v3, and USBID (apart from D+/D-).[/img]

[Ttelmah]

Both.

It means there has to be a physical connection to the USB V+ line, and the
software has to be told what pin to use for this sensing. On the DsPIC's,
you normally do it with the Vbus pin, and the VBUSVD bit. You setup a
USB_CABLE_IS_ATTACHED macro, before loading the USB driver to test
this bit.

This is _required_ by the USB specs, unless the device is only powered
by the USB bus (so switches off when disconnected).

[robleso7473]

Hi Ttelmah,

Yes, I've had USB V+ connected VUSB pin on MCU from the beginning. I do understand this is required or recommended.

Thanks,
O.

[Ttelmah]

Good.
A lot of people don't realise this is required.