Config0 byte in I2C EEPROM showing bit 2 setting

Question: Why do some examples for the Config0 byte in I2C EEPROM show setting bit 2?

 

Answer:

In the early versions of FX2 this bit was used to permanently set the operation frequency of the 8051. In later versions of the silicon it was altered to allow the 8051 to set up and change the CPU clock speed. As a result, the production silicon does not use this configuration bit. The 8051 starts at 12 MHz and the 8051 has the ability to change the frequency through the CPUCS register. The examples allow both early and later version of the silicon to start the clock speed at the desired rate. These bits are not used in the current production silicon.