TL16C550D: TL16C550DPFB Asynchronous communication element - parallel to serial

I am trying to use two TL16C550DPFB (48pin TQFP at 5V DC) coupled to have single host microcontroller on parallel data communication side and the serial UART paths are independent to each other.

Being paralleled D0-D7 lines to host microcontroller, I am using chip select (CS2n) to select one data bus and keep the other at tri-state.

In my testing one chip is working and another not working. Please confirm whether the chip select ( CS0, CS1 & CS2n) inactive makes the data bus trip-state?

Are there any other factors for me to consider?

Thanks

Ram