Overall Control System; A. Video Controller Pcb - Canon LBP 2460 - B/W Laser Printer Service Manual

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