Be cautious on putting much capacitance on the lines. It will have a definite effect on the signal rise times, which define the timing for the transfers. The I2C spec has a maximum bus capacitance spec. Noting this, however, the biggest effect will be to hurt operation at high speeds. Slowing down the bus tends to counter the effect of bus capacitance. If you can tolerate 50KHz or slower (almost all I2C devices will), then you should be just fine. Just don't expect 400KHz operation with 40 or 50pF of capacitance on the lines...
On May 7, 2008, at 2:53 PM, John H. Fisher wrote: > Thank you very much for this tip. I was afraid to put caps on the > sda/scl lines and now I wish I had. Thank you very much :-) > > py2wm wrote: >> >> .. I have had trouble controlling the >>> WB6DHW board probably because of RF feedback and bad grounding on my >>> part. >> >> I've also had this same problem while controlling the Si570 chip from >> the PC parallel port. The symptom was the chip not giving out the >> correct frequency or simply not obeying to the software. The problem >> went away after I added 33pF capacitors at the SCL and SDA inputs >> (header H2) in WB6DHW board. The capacitors leads must be as short as >> possible, SMD types are prefered. The 33pF value is good to the >> intended range (10-200 MHz), a higher value may distort the shape of >> the parallel signals. >> >> It now works smoothly, I specially enjoy SWLing using I2PHD's Winrad >> which does a fine job of controlling the 570 chip with PE1NNZ's DLL. >> >> 73, >> >> JK De Marco, PY2WM >> >> > > -- > Regards, > John > > ========================================================= > email: [EMAIL PROTECTED] > photos: http://www.flickr.com/photos/k5jhf/sets/ > videos: http://www.youtube.com/profile?user=k5jhf > files: http://briefcase.yahoo.com/[EMAIL PROTECTED] > web page: http://www.geocities.com/[EMAIL PROTECTED] > call sign: K5JHF > ========================================================= > > > ------------------------------------ > > Yahoo! Groups Links > > > -Jack Brindle, W6FB =======================================================================
