TCN75 and 89C51 microcontroller interface circuit as shown. The address will TCN75 A2 ~ A0 inputs are connected to the high UDD, set the address code is 111. 89C51 chip select via software to function. 89C51 serial data receiver (RXD) and serial data transmitter (TXD) in turn connected TCN75 the SDA, SCL side. TCN75 interrupt / compare interrupt signal received 89C51 end INT0.