From B777Boeings
In flight, the pitch trim switches do not position the
stabilizer directly, but make inputs to the PFCs to change the trim reference speed.
One interesting point that takes some getting used to is that it does not matter which way you select the pitch trim switches in the B777 for a speed change. Inflight all the trim switches do is tell the PFC of a need to change trim reference speed whether you trim forward or back makes no difference.