Question: Can I change the clock rate of the I2C device to 100 kHz after startup? Must it be 400 kHz at startup to properly enumerate?
The bus frequency defaults to approximately 100 kHz for compatibility, but you can configure it to run at 400 kHz for devices that support the higher speed. Setting bit 0 of I2CTL (E67A) register to 1 causes EZ-USB to drive SCL at approximately 400 kHz. When the CPU begins to run, firmware can modify the I2CTL.0 bit.