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pull up resistors with TWI higher speeds

 
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hgrueneis

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Joined: 04 Apr 2009
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Location: A-4786 Brunnenthal

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PostPosted: Thu Aug 04, 2011 8:13 pm    Post subject: pull up resistors with TWI higher speeds Reply with quote

Further experimenting with TWI clock speeds of about 800 KHz (by setting the registers directly) I have noticed that a perfect waveform on the clock signal does not work so well. A much higher pull up value is needed on the clock than on the data line.
I used 1 to 2 Kohm on data but 4K7 on the clock, then it works fine. Adapting the pullup with scope to a perfect
50% duty clock did not work.
Hope this helps a bit.
Also the new slave lbx for TWI is much faster than pushall/popall of course because there are not as many registers saved.
Hubert
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