PCF8951读程序

unsigned char AD_Read(){    unsigned char tmp;iic_start();iic_send_byte(0x90);if(0 == ack){    return ERR;}iic_send_byte(0x40);if(0 == ack){    return ERR;}iic_start();iic_send_byte(0x91);if(0 == ack){    return ERR;}tmp = iic_rev_byte();iic_noack();iic_stop();return tmp;}