HP Color LaserJet CM4730 Service Manual - Page 179

Sub power supply assembly The sub power assembly provides power to the ADF and the image scanner. It is connected to the low-voltage power supply and the DC controller. Video interface control The video interface allows communication between the formatter and the DC controller. The formatter always monitors the status of the MFP by using the video interface. It sends the VIDEO signals to the DC controller through the video interface when the MFP is ready to print. The DC controller turns the laser on or off based on the signals it receives. Figure 4-12 Video interface control The VIDEO INTERFACE signal is exchanged during printing operations, as described below. 1. When the MFP engine is ready to print, the DC controller notifies the formatter using the STATUS COMMAND signal (SC). 2. The formatter sends a print command as a SC signal to the DC controller when the MFP engine and the data for one page are ready. 3. The DC controller drives the scanner motor and sends the HORIZONTAL SYNCHRONOUS signals to the formatter after receiving the print command. 4. The printer engine starts a pickup operation. When the paper arrives at the top of page sensor (SR12), the DC controller sends the VERTICAL SYNCHRONOUS signal (/TOP) to the formatter. 5. The formatter sends VIDEO signals in synchronization with the HORIZONTAL SYNCHRONOUS signals to the DC controller upon a reception of the /TOP signal. 6. The DC controller controls each color's laser driver circuit and turns the laser on and off according to the VIDEO signals. This forms an electrostatic latent image on the photosensitive drums of each color. ENWW Engine control system 159