Grant Brown wrote:
> Hi Jan
> 
> Read the data sheet, gee thanks for the tip.
> 
>>> Not possible. The data sheet is perfectly clear on this.
> 
> 
> The data sheet that I have for the PIC18F45J10 says 20Mhz crystals are 
> OK and have been tested with the device.

But that wasn't what you asked about :

 >> I have a external 20Mhz crystal as the clock input and wish to run
 >> the device at its maximum speed of 40Mhz

I read that as that you want to *both* use a 20 MHz crystal
*and* run at 40 Mhz at the same time. Was that wrong !?

My best tip is still to re-read the datasheet.

If you want to run at 40 MHz, you must either supply an
externa 40 MHz clock or use a 10 Mhz crystal with
the 4x PLL (the most common setup).

Using a 20 MHz crystal, you can only run at 20 MHz.

Jan-Erik.

> 
> Table 2-2   page 26
> 
> But anyway thanks for taking the time to respond.
> 
> Kind Regards
> Grant Brown
> 
> Jan-Erik Soderholm wrote:
>> Grant Brown wrote:
>>   
>>> Hi list,
>>>
>>> Starting to use a PIC18F45J10 for the first time.
>>>     
>> Right, start with the datasheet, in particular the chapter
>> on the oscillator configurations. It's just a couple
>> of pages.
>>
>>   
>>> I have a external 20Mhz crystal as the clock input and wish to run 
>>> the device at its maximum speed of 40Mhz
>>>     
>> Not possible. The datasheet is perfectly clear on this.
>>
>> Jan-Erik.
>>   
> 
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