Matrix user forums

HI Guys,

I have one small question,

I recently bought a PIC18F4455 Microcontroller. But I dont have the wright Crystal. On my EB006 board there is an 19.6608 MHz crystal. But the 18F4455 doesn't work @ that frequency.

I want to use the USB functionality of this device, I don't care for Full ore Low speed USB transfer. But the questions is. What crystal should I use and what capacitance does it need.

Do I use an 48 Mhz crystal ??? pF
Ore an 20 MHz crystal 18 pF >>>> http://www.produktinfo.conrad.com/daten ... C49_4H.pdf

Can some one help me out.

Thanks.

Regards Jordy Kleian

PS. Can you expand your programming memory, I have an 16F877a this device has 8192 single word instructions and 14.3K bytes. Is there any way you can expand this.

Hi,

I'm using a 4MHz crystal on the multiprogrammer board with the 18F4455 (and 18F2455) then you need to set the config of the microcontroller right.

It should work with a 20MHz crystal.

Regards,

Nicolas L. F.


PS : http://www.matrixmultimedia.com/Learnin ... -1_Web.pdf
Take a look at the config screen on page 3, that's for a 4MHz crystal but you'll need to change the OSC Select and maybe the CPU Sys CLK Select (I think that's it) .

What Nicolas states, is spot on. The 18F4455 has a PLL multiplier. This means that with an external 4,8,12,16,20MHz Etc crystal, the Chip oscillator will run at 48MHz.
I have created a Flowchart with 1Hz flasher on port A0, and osc set at 48MHz that will work for EB006 with a 19.66MHz xtal, Since it is near to 20MHz, the PLL will work OK.
USB function should also work.

I knew I forgot to say something !

What hasn't been told yet, is that in flowcode, you need to set the frequency to 48MHz instead of 19.66MHz or 4MHz or ...

Cheers

EDIT:

... and osc set at 48MHz ...

Ah sorry I must have missed that