# Can I use a single crystal oscillator for multiple ICs? [duplicate]

Possible Duplicate:
What's the schematic to share one crystal with two micros?

## Background

I am building an Arduino project that basically consists of five Bareduinos.

## Question

Can I share a single 16Mhz crystal with multiple ICs (ATMega328), or does each IC have to have its own crystal?

If each does need its own crystal, will I have any execution latency among the various ICs? For example, if I send a signal from one IC to four other ICs, telling them to each to start blinking their own LED, would the LED blinking be synchronized or slightly out-of-sync?

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Or this one electronics.stackexchange.com/questions/27989/… where I explain that some microcontrollers (AVR) can output the buffered crystal clock on one of its pins. –  jippie Jun 17 '12 at 7:28
this is a duplicate to me, but as a side note you could ask a question about how much this would desync them. An important note here, 100 clock cycles out of sync(which is a crazy amount) would not be visible to your eye at all, it would have to be orders of magnitude greater desync –  Kortuk Jun 17 '12 at 20:08
Is there no difference between sharing a single crystal between two ICs and sharing a single crystal between 5 ICs? If there is a difference, this question would not be a duplicate and someone else may need the same answer. –  Matthew Patrick Cashatt Jun 17 '12 at 21:50

## marked as duplicate by stevenvh, Kortuk♦Jun 17 '12 at 20:10

The ATMega328 has a full-swing oscillator, with rail-to-rail swing on the XTAL2 output. Buffer it with a 74HC1G14 Schmitt-trigger, and you have a clock you can distribute to the other controllers. The Schmitt-trigger has an input capacitance of typically 1.5 pF, so you may want to subtract that from the oscillator's load capacitance.

This clock can drive the XTAL1 inputs of the other devices directly. I would suggest to keep connections as short as possible, because they will cause a lot of radiation. You can limit that by using an RC filter at the Schmitt-trigger's output. A 100 $\Omega$ resistor plus a 15 pF capacitor give you a cutoff frequency of 100 MHz.

Don't forget to program the CKSEL fuses on the other devices to "0000".

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THANK YOU SIR!! –  Matthew Patrick Cashatt Jun 17 '12 at 11:52