Hi,
Dont know if this helps understanding. The new Hyundai system is using Bosch 3, it has inlet control only, which means a voltage is required to give full pressure and no voltage shut down. The bosch 2 system had inlet control which was open with no voltage but the rail pressure regulator controlled the finer tuning, so this was teh failsafe. Frnak massey gives a good example in one of his videos when he is using s bit of kit to control pump pressure indfepend of PCM.
Hope this is of help.
Jim