With the addition of the External I2C Slave-Control driver, PSoC Express provides all of the necessary design elements for the implementation of an I2C master device to fulfill monitoring and control functions in master/slave system designs using the industry standard I2C bus. This Application Note is a follow up to AN2351, “Implementing Inter-Device Communication with PSoC Express.” Here in we introduce the External I2C Slave-Control driver, which allows you to write to an I2C slave device, be it a commodity sensor or a PSoC Express custom slave design, as well as discuss the External I2C Slave-Monitor driver. Two example projects are presented that demonstrate the control and monitoring of an I2C slave by a PSoC Express design.