IM153-2 and DP/PA coupler and IO

The machine now:
- 1st S7-rail with CPU and 8 IO-modules
- 2nd rail with IM153-2 and DP/PA coupler(FDC 157-0)

My question: we need another digital output- and inputcard, but we don't have any more space on the first rail.

I don't know if its possible to integrate this in the 2nd rail ?? Or is there another possibility, or do i need another rail... ?

As far as I know, you cannot add IO modules to a DP/PA coupler rack.

You have two options, if you want to use S7300/ET200M IO:

1) Add a rack extension, with an IM360/IM361 or a pair of IM365s
2) use it as remote IO, with either a PN or DP interface module.