AC500 HA MTCP | serial port

Dear All,

I'm planning to use AC500 HA MTCP redundant system. I need to have one serial port for modbus RTU, what module is suitable to use in a remote rack(next to CI52x module).

also, if i want the plc to communicate with modbus RTU slave, can i use the embedded serial Port on the redundant plc, and if i do so can i connect them in parallel

Thanks in advance.