Dear experts,
We have a PIC MCU, an Altera Flex10k10 (EPF10K10ATC100-3) and a serial EEPROM connected to a I2C bus. The PIC and EEPROM are 5V devices, the FPGA is a 3,3V device with MultiVolt IOs. There is a I2C slave controller implemented in the FPGA that is definitely working correct. Our problem is that we are experiencing difficulties when writing from the PIC to the FPGA over I2C. The FPGA doesn't read the correct bytes (it reads 0xFFs). It didn't help to change the pull-ups from 400R to 1K, 4K7, 10K! Now, we realized that communication works if we connect 5,6V to the pull-ups instead 4,7V as we used before. Can somebody please explain why this solved our problem? Currently it is more a workaround than a solution since we don't know what exactly our problem is.
Thank you in advance.
Best regards, Markus