I'm using a chip that needs a 6MHz crystal on it. All of the regular 2 pin crystals are very large for this application, so I was looking into the smaller profile oscillators. This is the chip in question:


I'm familiar with hooking up 2-pin crystals where they connect to the XTAL1 and XTAL2 pins and have external pF capacitors to ground, as well as the 4-pin ICs with 2 GND pins and the XTAL ones, but all of the 6MHz oscillators I'm looking at seem to be different. They are 4-pin devices with this setup:

1: Tri-state 2: Output 3: Ground 4: VDD

Those connections seem straightforward too, but my question is about the XTAL pins. Can I connect the oscillator output to XTAL1 and leave XTAL2 floating? Or do I need to pull it up or down, or can I even use one of these oscillators with 1 output and no input? One of the oscillators I was looking at was this one:


Thanks for any help!

  • \$\begingroup\$ It depends what XTAL1 and XTAL2 are. One is an output and the other is an input. You can connect the oscillator to the input and leave the output floating. The datasheet will tell you this, and tell you which is which. \$\endgroup\$
    – user16324
    Oct 15, 2020 at 18:50
  • \$\begingroup\$ Did you read the datasheet? If not, why not? You'd have the answer faster from there instead of waiting for an answer here, and, we would have to find, open, and read the datasheet too to answer this. \$\endgroup\$
    – Justme
    Oct 15, 2020 at 19:03
  • \$\begingroup\$ Thanks for the replies! I've read the data sheet but missed that line, and wasn't sure if it was specific to this chip or if it was a general rule that wouldn't be in the sheet \$\endgroup\$
    – Evan
    Oct 15, 2020 at 20:44

1 Answer 1


To quote the information from the datasheet of the part you referenced:

However, a 6-MHz oscillator may be used by connecting the output to the XTAL1 pin and leaving the XTAL2 pin open.

So yes, you should leave XTAL2 open if driving XTAL1 with an externally generated clock signal.

  • \$\begingroup\$ Awesome, I've been poring through data sheets and missed that tidbit, and wasn't sure if it was a general rule that wouldn't be in there or device specific thing. Thank you! \$\endgroup\$
    – Evan
    Oct 15, 2020 at 20:42
  • \$\begingroup\$ I would not assume it's a general rule. In some cases it's to be grounded, others pulled high through a resistor. I just depends on the design of the chip. But regardless of what it's supposed to be, it should be in the data sheet. \$\endgroup\$
    – jwh20
    Oct 15, 2020 at 20:51

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