Quote Originally Posted by tamersoss View Post
Dear melanie .... i will try your suggestion ... i saw this table and i wondered why 40 mhz is not included ... you explained it ... the datasheet says at the very begining that max freq. is 40 mhz (not max external oscillator frequency) ... i will try and let you know the result ... however , many thanks for your kind concern.
It's probably not the PIC's fault that it won't run at 40Mhz, it's probably the circuit board's fault. The PIC will run all day at 40Mhz (55Mhz for one of mine that I pushed up a bit) even with an external 40Mhz. The key is a well designed 40Mhz external oscillator. There's a dozen reasons why a 40Mhz crystal won't run if it's not built right, especially if you're using one of those plastic solderless breadboards. Besides that, the external 10Mhz will keep down EMI over the whole circuit board.