CCS C Software and Maintenance Offers
FAQFAQ   FAQForum Help   FAQOfficial CCS Support   SearchSearch  RegisterRegister 

ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to support@ccsinfo.com
Capacitor value for 18F4520's 40Mhz Crystal value

 
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion
View previous topic :: View next topic  
Author Message
neverlog



Joined: 02 May 2010
Posts: 36

View user's profile Send private message

Capacitor value for 18F4520's 40Mhz Crystal value
PostPosted: Sat Jul 10, 2010 7:23 am     Reply with quote
Dear All,

Is the 18F4520 support 40Mhz?

if yes, what is the capacitor value for 40Mhz crystal?

Please help me. Thanks!

I am trying to search the datasheet, but it only give capacitor value for 25Mhz.
bungee-



Joined: 27 Jun 2007
Posts: 206

View user's profile Send private message

PostPosted: Sat Jul 10, 2010 7:49 am     Reply with quote
I usually put 12pF capacitors there. But It should be tested for yor application.
On other hand, you could use resonator or oscillator for more precision for your application.
mkuang



Joined: 14 Dec 2007
Posts: 257

View user's profile Send private message Send e-mail

PostPosted: Sat Jul 10, 2010 10:35 am     Reply with quote
There were previous posts about how you will have stability issues using a 40Mhz crystal. A better option might be to use a 10Mhz and PLL it up to 40 Mhz.
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

View user's profile Send private message

PostPosted: Sat Jul 10, 2010 12:08 pm     Reply with quote
Quote:
Is the 18F4520 support 40Mhz?

if yes, what is the capacitor value for 40Mhz crystal?


Look in this section of the 18F4520 data sheet:
Quote:
TABLE 26-6: EXTERNAL CLOCK TIMING REQUIREMENTS

It says the highest frequency for HS mode is 25 MHz. So you can't use
a 40 MHz crystal. You have to use 10 MHz and 4x PLL as explained in a
previous post.

You can use an external 40 MHz oscillator, but it's cheaper to use the
10 MHz crystal and PLL.
neverlog



Joined: 02 May 2010
Posts: 36

View user's profile Send private message

PostPosted: Mon Jul 12, 2010 7:56 pm     Reply with quote
Thank you for all the reply and the advice!
neverlog



Joined: 02 May 2010
Posts: 36

View user's profile Send private message

PostPosted: Mon Jul 12, 2010 7:59 pm     Reply with quote
Hi,

Can any one have any good reference for how to use 10 MHz and 4x PLL ?

Thanks in advance!
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

View user's profile Send private message

PostPosted: Mon Jul 12, 2010 8:23 pm     Reply with quote
Example program:
http://www.ccsinfo.com/forum/viewtopic.php?t=29761&start=1
neverlog



Joined: 02 May 2010
Posts: 36

View user's profile Send private message

PostPosted: Mon Jul 12, 2010 10:25 pm     Reply with quote
PCM programmer wrote:
Example program:
http://www.ccsinfo.com/forum/viewtopic.php?t=29761&start=1


Thanks for the help!!
Display posts from previous:   
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group