It's my understanding that the PLL has the effect of multiplying the frequency of your external oscillator by 4. So, if you put a 10 MHz crystal between OSC1 and 2 and activate the PLL, the chip will run at 40 MHz. My PIC18's haven't arrived yet though, so I very well could be wrong, but I think this is how it works. Daniel Imfeld ----- Original Message ----- From: "Mike Harrison" To: Sent: Thursday, February 13, 2003 11:00 AM Subject: [pic]: Ext Osc + PLL on 18cxx2 ? Looking at the 18Fxx2 datasheet, it says that the PLL can only be used in HS crystal mode, but it's not clear whether or not you can apply an external clock in HS mode and use the PLL - anyone know if this is possible ? -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.