One thing to watch out for!
I'm not sure if it applies to all safety modules or just the ET200 safety modules, but I got bitten once and will never forget it.
Each input has a pair, and it's not the next sequential input. So if you have an e/stop and wire the first input into CH0, the other channel MUST go into it's respective input, which will NOT be CH1. On the 8-ch modules I was using, you had to wire them this way:
Input 0 and Input 4
Input 1 and Input 5
Input 2 and Input 6
Input 3 and Input 7
This doesn't help you with your immediate question, but it might save you having to re-wire half a panel like I did