HP LaserJet 4 Service Manual - Page 146

6 Each time the formatter receives a synchronized BD signal from the DC controller, the formatter sends a VIDEO data stream (VDO) to the DC controller. 7 After the DC controller receives the VDO data, the DC controller translates it into a VIDEO OUT signal (VDOUT) that switches the laser diode ON and OFF. 8 The laser beam, created by the laser diode, reflects off the scanner mirror onto the photosensitive drum to form a latent electrostatic image, writing a single line of print (dot) data. 9 After the last VDO line of dot data is sent from the formatter, the DC controller checks for another PRNT signal from the formatter. 10 If another PRNT signal is detected, the Print period continues with another page. 11 If the DC controller fails to receive a PRNT signal before the end of the page passes over the Input/Registration Sensor (PS1), the DC controller initiates the Last Rotation period. If the printer fails to perform correctly, the DC controller sends an appropriate status to the formatter PCA, and an error is displayed on the printer's control panel. Timing Diagrams The following timing diagram describes the operation of the printers. The "MP Tray Timing Diagram" was developed by running two consecutive prints on A4 paper. 5-34 Functional Overview