Hi Pelle,
Regarding Ultimation, it's not easy to condense here how the entire system works. But basically the key aspects you need to understand how the system works is basically that these faders user the same send/return lines, with similar voltages (to the VCA fader system), to control either the motor DC (motors on) or the VCA amp (motors off), the latter much like the VCA consoles.
All the rest you see on the fader is now controlled by the CA bus (digital bus), namely, the computer (through the CA card which replaced the Lights & Switches card on the non-ultimation system). Some of the controlled elements I already stated before: LEDs, switch, CUTs read/write, motors mode (on / off), thumbwheel group, etc. The CA bus is not a serial bus, but rather a parallel bus, were 8 bits are sent/return for read/write operations. The read/write operations are controlled in a polling fashion where the computer poles each fader in a bank (bay), bank by bank. The faders are not autonomous (asynchronous), they are slaved to the computer control. So, for write operations the computer has to WRITE 8 bits with the status it wants, for the read operation, the computer as to READ 8 bits with the status the fader has at that particular time.
While in the VCA faders the computer has direct access and even controls/powers directly some of the fader elements, such as LEDs, on the Ultimation this is not true.
There are two key elements to this system, the first is the BUS card. The BUS card is the card that is installed one per bay, which allows to connect 8 faders cartridges. This card is "intelligent", in the sense it's just not an interconnection bus card, because you have to issue the Fader Address to select which fader you want to read or write on the BUS. The Fader Address configures all the necessary electronics on the BUS card, which allows you to select the target fader (1-8) and make sure that on the other end of the BUS you have one fader talking with you and not all!
The third element, is the 352 card (control card), that exists on each fader. Each fader is composed by a sandwich style PCB, the 352 and 353 cards. The 352 handles all the CA bus logic and communication. After the fader selection, when you issue a read/write, you are interfacing with the 353 card, which in turn controls all the aspects I mentioned earlier.
I think this gives a pretty good picture of the overall system.
Cheers,
Artur