说明：  驱动IO扩展芯片PCA9539 pca9539是一个24针CMOS器件，提供16位的通用并行输入/输出（GPIO）与中断和I2C/SMBus应用，用来提高I2C飞利浦的I / O扩展家庭复位膨胀。
(Drive IO extension chip PCA9539 The PCA9539 is a 24-pin CMOS device that provide 16 bits ofGeneral Purpose parallel Input/Output (GPIO) expansion with interrupt and reset for I2C/SMBus applications and was developedto enhance the Philips family of I2C I/O expanders.)