O U T L I N; Video Control System - Canon LBP-2000 Service Manual

VI. VIDEO CONTROL SYSTEM
A. Outline of the Electrical Curcuitry
1 . O u t l i n e
This circuit is designed to receive print data consisting of code data or image data from an external
device (e.g., host computer) through an interface cable.
The circuit processes the print data it has received based on the instructions from the control
panel for conversion into dot data.
The resulting dot data is then converted into video signals, which are sent to the DC controller
for control of the laser diode.
The arrangement used in the circuit is shown in Figure 2-6-1, and its block diagram is given as
Figure 2-6-2.
2 . Outline of the operation of each block
a . CPU
The CPU is a 64-bit RISC microprocessor. It has a circuit construction suited to the control of an
LBP, and controls the operation of the Printer according to the program stored in ROM. Its main
functions are as follows:
1 . controlling the SDRAM
2 . controlling the ROM
3 . controlling the video controller interface, HDD interface, and expansion interface
4 . communicating with the engine
5 . controlling the IEEE 1284 parallel port interface
6 . controlling the compression/expansion of image data
b . ASIC
The ASIC is used to control the operation of the video controller circuit according to the control
program stored in ROM. Its main functions are as follows:
1 . controlling of image smoothing operation
2 . controlling the EEPROM
3 . controlling the option panel interface
c . DRAM
The DRAM possesses 4 M of memory, and stores the following data items:
1 . print data from external devices (reception buffer)
2 . pattern data resulting from conversion of code data or image data
3 . fonts processed by the video controller
A slot for expansion is also provided, enabling expansion to as much as 72 MB by fitting an
expansion RAM DIMM (32 M or 64 M) into the slot found on the video controller PCB.
d . Built-In Program ROM
The built-in program ROM possesses 8 MB of memory, and stores data for operation sequence
control by the video controller circuit and residual fonts.
e . Expansion ROM DIMM (J1, J2, J3)
The expansion ROM DIMM may be enhanced by a ROM DIMM for upgrading, Font ROM DIMM as
an option, and Flash ROM DIMM; as many as 3 pieces may be installed, and any slot may be used
for installation.
CHAPTER 2
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