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Author Topic: I2C between 8MHZ & 16 MHz arduinos  (Read 495 times)
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magnethead794
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« on: August 31, 2012, 09:47:43 pm »
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Any issues with doing it? Just wondering. Need to link a FIO and a mega over I2C.
Yes I know level conversion will be needed.

(the other end of the xBee link is a FIO & teensy2.0++ pairing..same deal there)
« Last Edit: August 31, 2012, 09:54:59 pm by magnethead794 » Logged
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frank26080115
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« Reply #1 on: August 31, 2012, 10:29:20 pm »
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there shouldn't be any issues

level conversion will not be needed, just disable internal pull-up resistors and use external pull-up resistors that "pull" to 3.3V
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magnethead794
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« Reply #2 on: August 31, 2012, 10:43:13 pm »
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Quote from: frank26080115 on August 31, 2012, 10:29:20 pm
there shouldn't be any issues

level conversion will not be needed, just disable internal pull-up resistors and use external pull-up resistors that "pull" to 3.3V

So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
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James C4S
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« Reply #3 on: August 31, 2012, 10:46:08 pm »
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Quote from: magnethead794 on August 31, 2012, 10:43:13 pm
So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
That's why you use external pull-up resistors.
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magnethead794
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« Reply #4 on: August 31, 2012, 10:51:40 pm »
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Quote from: James C4S on August 31, 2012, 10:46:08 pm
Quote from: magnethead794 on August 31, 2012, 10:43:13 pm
So the 5V signals coming from the 5V board won't overdrive the 3V3 pins?
That's why you use external pull-up resistors.

Doesn't make sense to me, but I'll go with it.
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James C4S
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« Reply #5 on: August 31, 2012, 10:54:38 pm »
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Research "open collector".

The I2C pins are open-collector.  They need to be pulled-up so if you external resistors and pull them up to 3.3V they become 3.3V pins.
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magnethead794
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« Reply #6 on: August 31, 2012, 10:58:52 pm »
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Quote from: James C4S on August 31, 2012, 10:54:38 pm
Research "open collector".

The I2C pins are open-collector.  They need to be pulled-up so if you external resistors and pull them up to 3.3V they become 3.3V pins.


works for me.
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