Canon LBP 2460 Service Manual - Page 106

CHAPTER 2 VI. OVERALL CONTROL SYSTEM A. Video Controller PCB 1. Outline The video controller PCB receives print data consisting of codes or image data from an external device (host computer, etc.) via the interface cable. The video controller PCB analyzes and processes the print data, including the items specified from the control panel, and converts it to dot data. The dot data is sent to the DC controller PCB to control laser diode emission. Figure 2-6-1 shows the layout of main ICs on the DC controller PCB, and Figure 2-6-2 is a block diagram. 2. Functions by block a. CPU (IC29) The CPU is an Intel 32-bit RISC microprocessor (A80960HD-66). The CPU produces and analyzes the various interface data, creates image data and processes commands via ASIC according to the control program stored in the ROM. b. ASIC (IC21) The ASIC contains a circuit which controls the LBP, and separately processes the ROM and RAM. ASIC controls the video controller according to the control program stored in the ROM. The main functions are; 1) Controls the reading and writing of data to and from the DRAM on the video controller and the expansion RAM SIMM. 2) Creates address information for accessing data from the ROM on the video controller and optional ROM DIMM. 3) Controls the video interface, expansion interface, and the standard-equipped bi-directional parallel interface (Centronics specifications). c. AIR (IC10) This ASIC has a built-in SRAM which contains a smoothing control circuit. The main functions are; 1) Controls image smoothing. 2) Controls output of the video signal to the DC Controller. 3) Controls the operation panel interface. 4) Creates address information for accessing data from the EEPROM on the video controller. d. DRAM The DRAM has a memory capacity of 4M and stores the following information. 1) Print data which is input from the external device (receive buffer). 2) Pattern data converted from code or image data (bit map memory). 3) Fonts processed within the video controller (font cache memory). The memory can be expanded to a maximum of 96M bytes by installing 1, 2, 4, 8, 16, or 32M byte SIMMs in the three slots on the video controller PCB. e. ROM DIMM The 4MB ROM DIMM is installed in one of the two ROM DIMM slots, in which operation sequence control program of video controller circuit and fonts are stored. An optional ROM DIMM can be installed in the other slot. f. EEPROM (IC11) The EEPROM is used to store printer factory defaults and those valuse changed from the control panel across job boundary and power cycles of the engine. 2 - 60