What device are you trying to talk to? Is there a chance that it doesn't ACK on address and the device in your prior application did? If the last bit of the address sent is low then the capacitor would keep the data line low long enough for your code to think it received an ACK and keep going. Without the cap, your code sees no ACK and stops. Just a hunch. Seeing your code and knowing what device you are trying to talk to would help. Ken -----Original Message----- From: dvdmods To: PICLIST@MITVMA.MIT.EDU Date: Tuesday, January 11, 2000 11:52 AM Subject: i2c help please >Hi >please help! >I have a small problem with i2c bus,I am using 12c508 pin 7 for data and pin >3 for clock (internal clock,masterclear off ) >the i2c device is standard < startbit/address/data/stopbit > > >The code will work fine if I have my scope lead connected to data line(pin >4) ,I think this is adding capacitance to this line >so i removed the scope lead and fitted 33pf capacitor between the data pin >and ground, this also worked fine >But if I remove the cap the pic 12c508 wont talk to the i2c device .. >I have also moved the data and clock to other pins on pic but have the same >problem. >I also tried to slow down the rate the pic sends data to i2c device still no >good.. > The code I am using, is one I have used many times to talk to other i2c >devices >but on this device I am having no joy. >the device has pull up10k resistors on data and clock lines >Can anyone help?? > >any help will be greatly appreciated >many thanks >Tom