Question: I'm using a PIC24FJ256GB110 connected via SPI to a CAN Bus Controller chip MCP2515. The MCP2515 requires a crystal connected to it but has a Clock Output pin for driving a connected MCU. So I was going to connect the Clkout from the MCP2515 to the MCU. 

My question is that in the [osillator data sheet](http://ww1.microchip.com/downloads/en/DeviceDoc/39700c.pdf) for the PIC24F family of processors it shows this external clock connection with a NOT Logic gate in the circuit. I usually get parts from farnell but struggling with what it is I need for this NOT gate. Can it be any general NOT Gate or is it something more specific then that, like a buffer or some sort of impedance magic? Or is it as simple as a single NOT gate used to "clean" up the clock signal?

Answer: 
It's just a gate to clean up the waveform (or just to indicate that there is a logic output driving the input)- it would not generally be used if you were employing a clock oscillator nearby the MCU such as [this](http://www.foxonline.com/pdfs/FXO_HC73.pdf) one (photo from Digikey.com). 

![enter image description here](https://i.stack.imgur.com/P18oc.png)

You could use a ST gate such as this [one](http://www.fairchildsemi.com/ds/NC/NC7S14.pdf), but usually it's not necessary.
These ([Pierce](https://en.wikipedia.org/wiki/Pierce_oscillator)) oscillators are commonly built around CMOS ports for their high impedance. Usually a [74HC04](http://www.nxp.com/documents/data_sheet/74HC_HCT04.pdf), [4069](http://www.cmos4000.com/cmos/4069.html) will do the job. Use the remaining ports as output buffer so do do not unnecessarily load the oscillator itself.

A Schmitt Trigger is **not** useful for a Pierce oscillator.

[Use of the CMOS Unbuffered Inverter in Oscillator Circuits - Texas Instruments](http://www.ti.com/litv/pdf/szza043) Especially check the chapter on *Practical Design Tips*