----- Original Message ----- From: "Jason White" > > Oscillator > - Would this go under external clock input mode ECIO ? Yes, but IMHO this is a bit overkill just for one MCU. As Lyle said, you can use a standard 10MHz crystal with the PLL * 4 to produce a clock of 40MHz on the 18F452. If you want to try overclocking though, then it may be necessary to do something along these lines, also I think you'll need to find a way of keeping it cool if you're gonna go for much more than 10-20% increase. With the 18F2455, 2550, 4455, 4550 you can go up to 48MHz, and they are far more flexible with the crystals - you can use from 4 to 48MHz crystals, and still use the PLL as it has an input divider from 1 to 12. For example, if you wanted 48MHz from a 20MHz crystal, you would set the PLL input divider to 5, to produce the required PLL input frequency (4 MHz), then the PLL produces 96MHz, and you set the PLL postscaler to divide by 2 (lowest possible) to produce 48MHz (12 MIPS) -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist