How do I use the MCU on the MAX9271 side to control the GPIO on the MAX9272 side through a coaxial or twisted pair cable?

Each SerDes device has two I²C device addresses stored. Register 0x00 in the MAX9271 corresponds to the I²C device address of the MAX9271. Register 0x01 corresponds to the I²C device address of the de-serializer (the MAX9272). By reading and writing to the I²C addresses listed in register 0x01, you can configure or read the status of the MAX9272. When operating on the GPIO of the MAX9272, the corresponding register is 0x0E (Refer to the register table in the MAX9272 data sheet).