pull up resistors with TWI higher speeds

hgrueneis · Joined: 04 Apr 2009 Posts: 906 Location: A-4786 Brunnenthal

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