Master&slave S7 cpu

Hi every one
Our system in configured with S7CPU 314 with some ET 200M and CP we are going to make communication between this CPU and other CPU may(S7 315/2DP)through DP profibus cable as(Master-Slave)
What kind of DP port we need to put in the old cpu rack to connect it to DP port in our new CPU(DP COUPLER-CP...)
Could we connect our new plc to the last ET in the old configuration
Thanks

Hello gh_ounie;
Trying to clarify what you are trying to do, here is a quick sketch of the network as I understand it; see the attached file.
If this reflects your design intent, then look at the following FAQ from siemens' support website:
http://support.automation.siemens.com/WW/view/en/6518938
It shows how to set a CPU 315-2DP as a slave to a CP 342-5 as DP master; there is an example program you can download to test the functionnalities; you then only have to modify it to suit your program.
Hope this helps,
Daniel Chartier