A320: Why do SDACs supply all three DMCs? On the Airbus A320, in the Electronic Instrument System (EIS), there are three Display Management Computers (DMCs):


DMC1 supplies the upper ECAM
DMC2 supplies the lower ECAM
DMC3 is a backup.


There are also two System Data Acquisition Concentrators (SDACs) that acquire system status, process it, and and send system page data to the three DMCs. 

Why would it send it to all the DMCs?

The Hydraulic System is displayed only on the lower ECAM which is supplied by the DMC2. Nothing about the hydraulic system is shown on the upper ECAM supplied by the DMC1. So why would SDACs send data to DMC1? I can understand why it would send it to the DMC3 because its a backup but why the DMC1?

Same thing for the Air Conditioning System, Electrical System, etc. None of those systems are displayed on the upper ECAM supplied by DMC1. The only thing displayed on the upper ECAM is engine and MEMO (or emergency stuff in the case of an emergency).

I guess the engine is a system but there is an engine system on the lower ECAM as well. The upper ECAM shows the engine performance and the lower shows the oil, so not the same thing.
The Hydraulic System is displayed only on the lower ECAM which is supplied by the DMC2. Nothing about the hydraulic system is shown on the upper ECAM supplied by the DMC1.


That is not true. If DMC1 or DMC2 fails, DMC3 takes over. But if the display fails, the other display takes over. So the hydraulics page can be displayed on the upper display. It can even be displayed instead of the MFD or even PFD if both ECAM displays fail. Similarly for all the other ECAM pages.