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
PIC18F87J50 USB osc configuration options

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



Joined: 17 Dec 2005
Posts: 58

View user's profile Send private message

PIC18F87J50 USB osc configuration options
PostPosted: Mon May 12, 2008 2:44 pm     Reply with quote
Im implementing USB in a mobile device. Using the PLL would draw too much current so I was hoping to just use a 24MHz crystal without the PLL enabled.

If I understand the datasheet correctly, I can use a 24Mhz crystal for USB low-speed operation. Would the USB work correctly using a 24Mhz crystal with PLL disabled?

Ideally I would like to run the device using the INTRC at 32khz to perform certain operations, then when the USB is plugged in (ill use usb-sense with an interrupt) switch over to the 24MHz crystal.

Being a mobile device I need to save as much power as possible when the USB is not connected.

thanks
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

View user's profile Send private message

PostPosted: Mon May 12, 2008 3:12 pm     Reply with quote
Look at this table in the PIC data sheet:
Quote:
TABLE 2-5: OSCILLATOR CONFIGURATION OPTIONS FOR USB OPERATION

The 5th entry shows that you can use a 24 MHz crystal or oscillator
(in HS or EC mode, respectively) to provide the PIC's clock frequency.
There is a note in the PLL Division column that says this configuration
is only valid for low-speed USB operation.
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