[request] 18f series usb programming

biomed12 · Joined: 05 Feb 2016 Posts: 33

Hello everyone,

I am a new 18f series programmer. Before, i worked with 16f877 for a few months and i know the bulk of its properties.

Considering it, is there anyone who suggests me something about how can i learn usb programming? How should i start? I don't have any idea and just i have started reading the usb section in datasheet of 18f4550.

Thanks.

temtronic · Posted: Tue Apr 19, 2016 2:10 pm

well CCS kindly supplies a few 'drivers' and WORKING USb example programs....
That's where I started. Just be sure your PIC does a 1HZ LED program properly before you try anything more complicated! The 4550 NEEDS the correct fuses set AND the proper crystal to get USB to run!

Jay

biomed12 · Joined: 05 Feb 2016 Posts: 33

temtronic · Posted: Wed Apr 20, 2016 4:53 am

If you want a book, buy Jan's! It's about 600+ pages long, dull and dreary AND goto the official USB.org website. Of course, goto Microchip and download every apnote they have on USB.
Do all that and you won't be back here for 3 or 4 months ! Lots of reading !! USB is very complicated and I wager 99% of those tech/engs that design with it don't KNOW 1% of what's really going on with it!!

I do know the CCS supplied drivers do work but if you need to know HOW it works , you need to understand the PIC at machine code level.The majority coming here for 'USB' only want it to work,don't care how it works.

Jay

Ttelmah · Joined: 11 Mar 2010 Posts: 19553

Seriously, USB is complex.
You need to pull the document from the USB committee "Universal serial bus specification Version 2.00".
Then get one of the books like Jan Axelson's "USB complete".
It is not a 'you send something' type bus. The bus itself is running continuously and talking to all the devices. The master initiates all transactions (though certain slaves have the 'concept' of being able to initiate a transaction, this is actually done when the master polls them).
The slave device _has_ to have code to identify when it receives a packet addressed to it, and when a packet it wants to send has been read. The CCS drivers do all of this for you (except handling things like mass storage device transmissions). However the 'hooks' to attach your own code for things like this are in the CCS drivers.
Look at the comments inside the CCS drivers as well. These are a large part of the documentation.

Ttelmah · Joined: 11 Mar 2010 Posts: 19553

Joke is I see Temtronic said exactly the same thing while I was typing!.

It is worth understanding, that even on the PC master, or any other slave device, you would never write the complete USB code yourself, unless you have several months to spend.
I've tweaked, and even re-written the CCS code for some special applications (things like a PIC18, that is both a CDC, and MSD device), but would still not consider writing from scratch for USB. The best way is to understand the phases of the USB operation, and how the enumerators work (and what is needed at the PC end for each type of enumerator), then just modify the enumerator, and use the off the shelf routines.
Add to the list a USB monitor program that can watch the packets in both directions, or a logic analyser with similar abilities. I could not have got the MSD to work without one or the other of these.

biomed12 · Joined: 05 Feb 2016 Posts: 33

biomed12 · Joined: 05 Feb 2016 Posts: 33

Ttelmah · Joined: 11 Mar 2010 Posts: 19553

With USB, the cdc interface can _emulate_ normal serial operations (as far as the code is concerned), but this needs a huge amount 'behind the scenes'. The slave has to send a CDC descriptor to the CPU when enumerated, then on the PC this automatically loads the serial emulation driver at the PC end.
Then if (for instance) the PC sets the serial rate on such an emulated port, this has no effect at all on the usb rate. Instead a packet is sent to the driver at the slave end to say 'this is the baud rate I want to use', which it can use to set the rate for an external connection, or completely ignore!...

The host initiates all transactions. A slave cannot start sending stuff without being asked. All communications are 'half duplex' (only one way ata a time on the bus).

Do a search for AN57294, which is a really nice document from Cypress that gives a good starting description of USB. It is aimed at people wanting to understand the bus for their controllers, but is totally applicable to all devices.

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Also, look at the manual for the CCS USB Development kit:
http://silanus.fr/sin/formationISN/Robotique/Logiciels/CCS/Data%20Sheets/Development%20Kit%20for%20the%20USB%20Exercise%20Book.pdf
You could buy their board (as a standalone, instead of the whole
development kit), or you could build it.