PIC24 Oscillator

dish_moose · Joined: 06 Oct 2006 Posts: 13

I have been looking at oscillator configs for a PIC24FJ128GA204 and I am getting more confused. I was reading this post: http://www.ccsinfo.com/forum/viewtopic.php?p=159723&highlight=crystal#159723. Does anybody have PIC24s going at a fast frequency? (I wanted to go 24MHz + 4x PLL = 96Mhz) I look at the data sheet and they state 8MHz is the fastest internal CLK with PLL but they do not state what the fastest Ext CLK is using PLL. I'm thinking I will have to start with the internal (8MHz) and switch to my EXT crystal + PLL. Has anybody done this?
-Bruce
Edit: the more I look at this 32MHz is as fast as this "puppy" is gonna go.

newguy · Joined: 24 Jun 2004 Posts: 1909

The issue I was having came down to a line buried in the datasheet. That particular dsPIC cannot be started from powerup with a 12MHz crystal. Lower values are okay, but 12MHz isn't guaranteed to start. That's why I had to use the internal oscillator initially, then perform the switchover to the external crystal & PLL.

I was a little annoyed that CCS sold (and I believe still sell) a kit that is equipped with a 12MHz crystal but they don't supply working code to automatically perform the switchover.

Consult the data sheet for your PIC. I'm willing to bet that your PIC has the same issue. If that's the case, using the code I posted as a guideline and the data sheet for your PIC, you should be able to get the internal/external switchover working just fine.

jeremiah · Joined: 20 Jul 2010 Posts: 1354

Typically the "FJ" parts are not the fast ones. You find more low power and general purpose PICs in this part of the family. Most PIC24FJ parts only going up to 32MHz (PLL) or 24ishMHz external.

Look at the PIC24EP or dsPIC. They allow the higher frequencies.