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I'm looking for the correct way to connect a 4-pin oscillator to a PIC24F. I have seen diagrams like the one below, but it seems that this connection is only for crystals and not crystal oscillators.

I've also seen on various forums (such as: http://forum.allaboutcircuits.com/showthread.php?t=76570) that the correct connection for a 4-pin oscillator is VDD to one pin, VSS to one pin, and OUT to CLKIN on the PIC24F.

Here is a link to the datasheet of one oscillator that I've been looking at: http://www.mouser.com/ds/2/3/ASFLMB-24525.pdf

This datasheet states: "Note:Recommend using an approximately 0.01uF bypass capacitor between PIN 2 and 4"

So my questions are: is the the correct way to connect a 4-pin osciallator? Also, do I need the external capacitors as shown in the image below for this type of oscillator? Or should I only connect the one cap between pins 2 and 4 as the oscillator datasheet recommends?

Crystal Connection

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Oscillator modules are quite compatible with PIC CLKIN pins. Just make sure that the power supplies are compatible i.e. don't use a 5V module if the PIC is running from 3V3. The one you linked to is 3V3 compatible so presumably your PIC is also running from 3V3?

You won't need C1 and C2 - they are needed when a XTAL is used.

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  • \$\begingroup\$ Well, it is actually a battery powered environment so the supply will be in the range of ~2.5 to ~3.3. I should at least install the cap between pin 2 and 4 as the oscillator datasheet suggests, correct? \$\endgroup\$
    – James
    May 12, 2014 at 19:04
  • \$\begingroup\$ Yes. However, I doubt you want to use the units you linked for. They are surface-mount and require reflow soldering. You should probably look for oscillators in a DIP package. \$\endgroup\$ May 12, 2014 at 19:18
  • \$\begingroup\$ It's a good point what @WhatRoughBeast says about soldering em down unless you have a PCB designed with a little bit of meat on the pads and some solder paste. Yes, the cap needs to be fitted. General rule if data sheet says do it then have a damn fine reason for not doing it!! You might be able to mount it upside down - I've done this sort of trick on prototypes before and it should work but make sure that 10nF cap is mounted close to the pads. \$\endgroup\$
    – Andy aka
    May 12, 2014 at 19:46
  • \$\begingroup\$ Thanks for the answers. I have one more quick question. What are the trade-offs in using a crystal like in the picture above instead of the oscillator? Less power and accuracy? \$\endgroup\$
    – James
    May 12, 2014 at 21:15
  • \$\begingroup\$ @James You'd have to check the data sheets and the accuracy specs on the caps (C1 and C2) to tell but I tend to think the module would be more accurate and have less temp coefficient in general. \$\endgroup\$
    – Andy aka
    May 12, 2014 at 21:26

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