Can I use CI 851A or CI854A with PM861 CPU or not?
You can use CI854A for S800 I/Os with PM861, i'm sure about this.
But for CI851 situation is little bit different, in 800xA v5.1 there was an hardware lib but in 800xA v6.0 there is no hardware lib for CI851, i think v6.0 does not support CI851 anymore. So it depends on 800xA version you want to use.
CI851A is an old verrsion Profibus DP Module and it is not supported in newer versions of ControlBuilderM (I think from ver. 4 above). CI854A is replacement of CI851A
But you can manually add this hardware library in case you have an older version of Control Builder M - e.g. ver. 3.2/16 (copy/paste files from older version to newer version)
Files for this hardware library are stored usually in follwoing directory (for newer versions):
C:\Program Files (x86)\ABB Industrial IT\Engineer IT\Compact Control Builder AC 800M 5.1\HWLibraries
Similar is also for older versions.
I did that when upgrade from 3.2/16 to 4.1 version - SCADA Portal to Compact 800HMI and it is working.
So if you have existing CI851A which you want to use in newer versions, you have to try described manual procedure.
You can contact me and I can try to send you old library files (strange why ABB doesn't save them anymore for upgrade purposes - probably CI851A is too old)
Better is to use CI854A