Video Control System; Video Controller Circuit - Canon LBP1760P Service Manual

CHAPTER 2
VI. VIDEO CONTROL SYSTEM
A. Video Controller Circuit
1. Outline
Video controller circuit receives print data consisting of code or image data from external device
(such as host computer) via interface cable.
The circuit analyzes and processes the print data including the data specified by the opera-
tion panel, and then converts them to the dot data. The dot data are sent to the engine con-
troller circuit to control the laser diode emission.
The layout of the main ICs on this circuit is in Figure 2-6-1, and the block diagram in Figure
2-6-2.
2. Operation
a. CPU (IC1)
A 32-bit RISC microprocessor (FC80960HD) made by Intel co. is used for the CPU in the print-
er, and its operation frequency is 50MHz. The CPU controls the operation of the video controller
circuit according to the control program stored in the ROM.
b. ASIC (IC2)
The ASIC is graphic co-processor and has the following functions.
1) DRAM control
2) ROM control
3) Video interface control
4) IEEE 1284 parallel port interface control
5) I/O bass interface support
c. ASIC (AIR, IC3)
The ASCI has smoothing control circuit and SRAM.
Its main functions are as follows.
1) Smoothing control of image
2) EEPROM control
3) Operation panel interface control
d. DRAM
4-Mbyte DRAM is installed on the video controller PCB.
72pin-DIMM of 4-, 8-, or 16-Mbyte can be installed to the two slots on the PCB.
e. ROM
A 4 Mbyte ROM is installed on the video controller PCB. In some cases, the 4 Mbyte ROM is
installed on the firmware ROM DIMM. In those cases, this ROM DIMM is installed in the con-
nector (J6) on the video controller PCB.
Of the three connectors, the two connectors, one in the middle (J7) and the other one at the
bottom (J8), can be used by the user to install 4 Mbyte or 8 Mbyte ROM DIMM. The connector
at the top (J6) is exclusively for the Firmware ROM DIMM.
f. EEPROM (IC10)
EEPROM is 4-Kbytes, and is used for storing the factory default value and the user set value
defined on the operation panel.
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