Canon LBP-1000, Service Manual

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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 (IC6)
This video controller uses a 32-bit RISC microprocessor (IBM25ACE4111PR) made by IBM Inc.
for the CPU, and its operation frequency is 66MHz. The CPU controls the video controller cir-
cuit operations according to the control program stored in the ROM. The CPU also has a circuit
suited for the LBP control as well as the following functions.
1) DRAM control
2) ROM control
3) Video interface control
4) IEEE 1284 parallel port interface control
b. ASIC (AIR, IC10)
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
c. DRAM (IC2/IC3)
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.
d. ROM (IC18)
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 (J8) on the video controller PCB.
Of the three connectors, the two connectors, one in the middle (J7) and the other one on the
left (J6), can be used by the user to install 4 Mbyte or 8 Mbyte ROM DIMM. The connector on
the right (J8) is exclusively for the Firmware ROM DIMM.
e. EEPROM (IC9)
EEPROM is memory enhancing 4 Kbytes available enough to delete electrically stored data or to
store new data, and is used for storing the factory default value and the user set value defined
on the operation panel.
CHAPTER 2
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