Xerox 4400DT - Phaser B/W Laser Printer Service Manual page 420

The toner adhering to the Magnetic Roller is always in contact with the drum surface.
When a less negative point on the drum (a discharged area) comes in contact with the
more negatively charged toner on the Magnetic Roller, toner transfers from the
Magnetic Roller to that point on the drum. At this point there is now a visible toner
image on the drum surface.
Block Diagram of the Development Process — Side View
Phaser 4400 Laser Printer Service Manual 8-7