S7-1200 <-> S7-1200 Modbus via RS232

[Homer_BL]

Hi all!

If I want to connect two S7-1200 CPUs with RS232 ports on both CPUs, and implement a Modbus RTU communication,
what is the cable pinout of a connecting cable?

Thanks.

 

[MikeDawkins]

Standard RS232 pinout : 2 - 3, 3 - 2, 5 - 5
But why go to the expense of comms modulas when the cpu has ethernet built in

 

[TurpoUrpo]

There is straight up example in siemens website for s7-1200 to s7-1200 modbus rtu comms with cp. But, I too wonder why modbus when there is ethernet integrated.