The functionality and differences in the functionality of the ROMON bit in the HC711E9 and HC711E20 microcontrollers (MCU) are discussed in this engineering bulletin. Although all 68HC11 Family parts are designed with full code compatibility in mind, bits may vary slightly due to customer-specific requirements in the CONFIG register. As a rule of thumb, however, the configuration bits should be similar from series to series within the family, having only slight differences.