FCDC-3 - Backwards compatibility
From Zenitel Wiki
The FCDC-3 is fully compatible with FCDC-1, FCDC-2 and TFIX stations/Ex Access Panels after these devices have been upgraded to software version 4.1.3.13 or newer.
Note that the FCDC-3 connected with FCDC-1, FCDC-2 and TFIX stations/Ex Access Panels running software version 4.1.3.12 or older is not compatible.
If you mix FCDC1/2/Ex stations with software version 4.1.2.12 (or older) and version 4.1.2.13 (or newer)