connect the first pin of the PCF8574 to the VSS of the LCD, 2nd pin to the VCC and so on. The input pins of the PCF8574 i.e. SCL and SDA should be connected with the SCL and SDA of the microcontroller.
We continuously check for incoming data and when data is received, display it on the lcd.
2.) Use interrupt. Microcontroller does it’s normal operations, and whenever the data receiving completes, an interrupt is generated and ISR is executed, after completing ISR, control returns back to normal operation.