Pretty good references Starbear.
On both Airbus (post 300/A310) and Boeing (post B767) altitude capture is actually done by using V/S mode. It is hidden by either ALT * (Airbus) or the ALT alert box (Boeing).
The mode change is triggered by reaching the calculated ROC for the trajectory intercept of the altitude. It is is approx equal to 10% of the ROC or ROD.
It then follows a parabolic path to the level off pont. The required parameters for the first segment thereafter are first cruise speed, pitch attitude for that speed, required thrust (all derived from the FMC and associated performance databases). The AFCS trims as required.
Although SPD my be displayed in the A/THR channel, the auto thrust is actually monitoring Vmin/Vls and Vmo/Vfe -5. (see your FCOM for which is which for your manufacturer.
The actual V/S mode was invented by Douglas for the DC10 AFCS. It made its way to Airbus and Boeing.
It can be an automation trap if you do not know what you are doing.
