Can two MUX8 boards be connected together?

The rule is that two MUX8 boards can be wired in parallel but not in series. So don't try and place one downstream off of another MUX8.

Connecting MUX8 in series is not recommended as daisy chaining will add signal skew and will cause comm problem. Since the mux8 has strong biasing (pull up/pull down) to maintain signal marking when not driven, more than two of them connecting in parallel will overload the RS485 transceiver.