USB pins

[achillis1]

Hello,

If I use the USB component of a PIC (16F877A, 18F4550) which are the pins and ports used for it?

Thank you in advance,

Best Regards,

Andreas Achilleos

[Benj]

Hello,

The 16F877A does not have the USB functionality.

The 18F4550 has 3 pins on port C which are used for USB comms.

These pins are marked on the Flowcode chip diagram.

D+ - USB D+ Signal
D- - USB D- Signal
Vusb - USB regulator output - connects to an external 220nF capacitor between Vusb and ground.

As well as the USB signals you also have to use a supported oscillator configuration. My advise is to use a crystal with one of the following frequencies. Any frequency can be used, the microcontroller will still run at the same speed 12MIPs.

Compatible crystal frequencies - 4MHz, 8MHz, 12MHz, 16MHz, 20MHz

Configuration settings for the device should be loaded as seen here:
http://www.matrixmultimedia.com/resourc ... %20PIC.pdf

And here is the link to the Article
http://www.matrixmultimedia.com/article.php?a=363

[JohnCrow]

Hi Andreas

The 16F877A does not have USB built in.

The 18F4550 is on port C, not sure which pins without looking in the datasheets though.
You should be able to see it by viewing the chip pinout in flowcode though.
If using the E-block the information should be on the data file that goes with that too.

Remember to use a 4MHz crystal, setup the advanced settings and change flowcode frequency to 48MHz
There are posts that cover setting up in some depth on this forum
Regards John

[JohnCrow]

Looks like we posted almost at the same time:)

[Benj]

Sorry John must have just beat you to it, looks like you answer has more info anyway.

Cheers for posting

[achillis1]

Thanks a lot!!!

Yes, sorry about the 16F877A!

I did searched about usb connection to find a previous topic but I must be blind


John says to use a 4Mhz crystal, can't I use the 20 Mhz?

Never the less I have a ready made board with 18F4550 and built in USB adaptor so I think that for the moment I will not be bothering with crystals!

Thanks again!

[Benj]

Hello,

You can use any of the following crystal frequencies.

4MHz, 8MHz, 12MHz, 16MHz, 20MHz

I have also been informed that you can set the config setting to use the 20MHz option and then use the standard 19.6608MHz crystal we supply on our hardware. This seems to work reliably but I wouldn't recommended it for actual wholesale products.

[achillis1]

!!! why not use it for actual wholesale products?

By the way, does your products pass for the CE marking?

[Benj]

I wouldn't use the 19.6608 MHz crystal for wholesale products as it is out of tolerance for the device. E.g. it is not the 20MHz crystal specified and while it may work in one offs there may be problems with mass markets and slightly less tolerant USB host hardware.

Yes all of our products are CE approved.

[achillis1]

Ok, Thanks BEn!