RS485 is a TTL to RS485 convertor.
RS485 is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems, widely used in industrial field. multipoint systems are supported.
It's used to convert the TTL standard to the RS485 standard. If the outside serial device is RS485 standard, you can attach this unit onto M5stack, therefore, to implement the communication with RS485 device by TTL protocol.