Canon CLBP-460PS, Service Manual

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VI.VIDEO CONTROL SYSTEM
A. Video Controller PCB
1. Outline
The video controller receives print data consisting of code data or image data sent from the exter-
nal device (host computer, etc.) via the interface cable.
Print data including contents specified by the control panel is analyzed, processed and con-
verted into dot data in the video controller.
Following this, dot data is output to the DC controller and turns ON/OFF the laser diode.
Figure 2-6-1 shows the location of the main ICs on the video controller. Figure 2-6-2 shows
its block diagram.
2. Function of blocks
a. CPU (U35)
The CPU is NEC-made RISC microcomputer (R4300). The CPU produces and analyzes various
interface data and generates image data and commands via ASIC according to the control pro-
gram stored in the ROM.
b. Memory ASIC (U4)
The Memory ASIC provides high speed interfaces between the CPU, memory and PCI bus. It
supports 64 MB DRAM DIMMs.
c. I/O ASIC (U3)
The I/O ASIC supports both internal and external I/O interfaces and performs the following
functions.
1) PCI direct memory control
2) Control panel interface control
3) IEEE 1284 parallel port (Centronics, Nebble, ECP) control
4) Serial interface control
d. Video ASIC (U7)
The video ASIC is a processor for graphics and performs the following functions.
1) PCI direct memory control
2) Decompression of compressed data
3) Video interface control
e. RAM DIMM
The RAM is not implemented on the video controller PCB for this printer. It is installed in the
DIMM slots (J6, J7, J8) on the PCB for use.
The RAM DIMM has a memory capacity of 32MB and stores the following information.
1) Print data input from the external device. (Receive buffer)
2) Pattern data converted from code data or image data. (Bit map memory)
3) Fonts processed in the video controller (Font cash memory)
f. ROM DIMM
The ROM is not implemented on the video controller PCB for this printer. It is installed in the
DIMM slot (J5) on the PCB for use.
The ROM DIMM has a memory capacity of 16MB and stores video operation sequences and
Postscript/PCL5C fonts.
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CHAPTER 2