The X9521 combines two Digitally Controlled Potentiometers (DCP's), and integrated EEPROM with Block LockTM protection. All functions of the X9521 are accessed by an industry standard 2-Wire serial interface. The DCP's of the X9521 may be utilized to control the bias and modulation currents of the laser diode in a Fiber Optic module. The 2 kbit integrated EEPROM may be used to store module definition data.