Canon Vizcam 1000, Service Manual

Page: 111 / 840

COPYRIGHT © 2001 CANON INC. CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
3-67
3. OPERATION AND TIMING
E. Video Controller
1. Outline
Figure 3-408 shows the video controller PCB, which controls the synchronization of video signals from
the image processor PCB and sends the video signals to the laser driver; the main functions of the circuits
are as follows:
1 Generates clock signals for synchronization control.
2 Controls synchronization in main/sub scanning direction.
3 Corrects density.
4 Counts video data units.
5 Generates image patterns.
Each of the Y, M, C, and Bk video signals compressed and stored on the IP memory PCB is read in sync
with the ITOP signal (image leading edge signal) and sent to the video controller PCB through the image
processor PCB. (See “Synchronization Control in Main/Sub Scanning Direction.”)
The video signals are then synchronized for the sub scanning direction based on the ITOP signal and
are subjected to gamma correction based on the conversion table in the density correction RAM. (See
“Density Correction.”)
Of the video signals after density correction, the Y and the M signals are sent to a special memory for
synchronization in the main scanning direction. Since the main scanning direction for the C and the Bk video
signals are opposite that of the Y and the M video signals, the writing direction is reversed before
transmission to the memory for synchronization in the main scanning direction. The synchronization for the
main scanning direction is by clock signals generated based on the BD signals. (See “Synchronization
Control for Main/Sub Scanning Direction.”)
Figure 3-408
Sub scanning
sync control
Y,M
C,Bk
Video data
counter
Gamma correction
Main scanning
synchronization
Main scanning
synchronization
BD signal
Y,M,C,Bk
Y,M,C,Bk
Y,M,C,Bk
Bk
Video controller PCB
ITOP signal
Read signal
Test pattern
generation
BD
detection
PCB
DC controller
Image processor PCB
Video signal
Video signal
Video signal
IP memory
PCB
C,Bk
Y,M
Laser driver PCB