Hallo!
H/w I use is 24LC512 5V I2C EEPROM. The chip is connected to the C167. The only I2C data line pulled-up via 5 kOhm resistor (clock line is not). Vcc connected to ground via 0.1 uF. Clock rate is about 125 kHz. I have no trouble neither with byte write, page write, random read operations driven via pin-bang routines. However I stucked on sequential read access when migrated to it from singe byte mode.
I use uVision Keil debugger and even in static go-through step-by-step manner still experience problem with reading 2nd, 3d, etc. bytes (the 1st byte is OK) - all I read is just FFh, i.e. data line being held high. My f/w does issue data, ACK/NOACK and clocks according to I2C specs (see below).
WHEN I connect scope probe to the data and clock lines to watch the waveforms, everything becomes OK, i.e. instead of FFh I get what should be! It remains to be OK if I hold scope's probe only at data line pin (i.e. seems this is OK to have no pull up at clock line at least in this particular case). As soon as I disconnect probe, I return back to trouble. With probes attached I see waveform timing is perfect and data are what I expect (I see them also in debugger).
So, I touch data pin with probe - good, disconnect the scope - have trouble.
Any idea what can cause the problem (might it be a purely electrical issue)?
Thanks, Nikolay.