USB Newbie needs starting guidelines

Neckruin · Joined: 17 Jan 2006 Posts: 66

Hi all,
Although I have been working with PICs for a long time, I have to use the USB capabilities of a PIC18 MCU for the first time in a new project.
At first I thought it would be as simple as the RS232 interface (adding a #use USB or similar and let's go) but after some days reading about this issue... I'm completely messed up and lost.
The PC software I have to comunicate with will be using the HID interface but we are going to develop our own protocol, data frames, etc.
I have no idea about how to begin to develop this code.
Do I need to define USB descriptors?
Can I avoid making this considering is a custom made application?
Where can I find a whole project example, not just the main c file?
I'm completely lost about how to begin this project and my boss is getting angry :S
Any help or guideline beyong the CCS examples will be welcome (or even a explanation about how to understand these)
Thanks a lot,

Juanma

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

Neckruin · Joined: 17 Jan 2006 Posts: 66

I have spent some time trying to understand the CCS examples, but it seems to me that they are made supposing a high previous USB knowledge.
I just don't know even how many files are required for a USB project to be developed or similar basic issues.

I'll try to compile a .c example and post any errors or dificulties I find.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

If you try the HID demo program from CCS, here's a tip about the
Hiddemo.exe windows application:

It has a button called "Establish Connection". But if press it, you will
get an error message, saying that the device is not selected.
To fix this, go to the "File" menu in the Hiddemo.exe program and click
on "Select Device". Then click on the CCS HID device in the list. Now
you can click on the "Establish Connection" button and it will work.
Then you can make the LEDs go on/off, etc.

Jim Hearne · Joined: 22 Dec 2003 Posts: 109 Location: West Sussex, UK

Does your project have to have true USB on it or could you get away with using a USB to serial convertor on the project so you are talking to the pic via a familiar serial interface.
On the pc end there is a USB driver (supplied by the USB-Serial chip maker) so the pc software thinks it's talking to a serial port.

This is how the CCS USB programmers work, they are still the serial versions really with a USB to serial converter chip tacked onto them.

Jim

Neckruin · Joined: 17 Jan 2006 Posts: 66

Jim Hearne · Joined: 22 Dec 2003 Posts: 109 Location: West Sussex, UK

Yup.
As long as you don't need the bandwidth of the proper usb it's a easy solution to making products USB compatible.

Look at the FTDI FT232 series of chips.
http://www.ftdichip.com/FTProducts.htm

Jim

Neckruin · Joined: 17 Jan 2006 Posts: 66

Thank you very much.
I'm already passing all this info to my partner who is going to work on the USB driver.
It can be a much faster way to solve this problem, at least from the low level software point of view.
I suppose the development will also be easier from the high level sw pov.

John P · Joined: 17 Sep 2003 Posts: 331

I've used the USB interface chips from FTDI, and I can report that they're easy to use at both ends of the cable. As has been said, as far as programming at the PC end is concerned, it looks like a serial port, and at the processor end, you talk to it via the UART. The one odd feature (maybe if I weren't such a USB newbie myself, I wouldn't call it odd) is that the number of the serial port is dependent on the individual chip you use, i.e. each one will get assigned a unique number and it increases with each new device you plug in. I think there's a way to defeat this feature, but so far I haven't needed to find it. But you do have to have software that can find a serial port that has almost any number. Is 255 the max? I think it is.

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

If you have a dedicated apllication at the PC side and don't need the virtual COM port feature, it's suitable to use the FTD2XX.DLL interface instead. It's also considerably faster and you have more options to enumerate individual adapters. Most existing solutions go this way, e.g. CCS ICD-U40.

When using VCOM interface, you can ease device selection by accessing windows registry information and avoid searching for unknown COM port numbers.

Neckruin · Joined: 17 Jan 2006 Posts: 66

Thank you guys,
This is all very interesting.
I hope is not too late to consider the hardware design changes this would involve.
We had already selected a PIC18F87J50 mcu, which is not easy to work with (at least for me).
By using an FTDI device we could select another PIC.
I'll have to talk with the hardware engineer.
Thanks again.

Juanma