COPYRIGHT © 1999 CANON INC. CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)B. Image Signal ProcessingThe printer board sends video signals (VDO0 through 7*; C, M, Y, and Bk, each rep-resenting 8-bit data) and CMD* signals (image mode switching command) to the DC con-troller PCB. The D-CPU (IC201) on the DC controller PCB is used to generate imagemode switch signals (VDATIN8*; Note) from CMD* signals.The video signals (DVDO0 through 7*) sent by the printer board *1 to the DC con-troller PCB are directed to a RAM (IC205; line memory) and then to a gate array (IC204).The video signals (DVDO0 through 7*) are subjected to image masking processing(p. 3-3) in IC204, and are sent to the PWM IC (IC208) as video data signals (VDATO0through 7). At the same time, the image mode switch signals (VDATIN8*) are movedthrough the gate array (IC204), and are sent to the PWM IC (IC208) as PWMF1 signals.Then, the video data signals (VDATO0 through 7) are turned into PWM demodulationsignals (VDATA*; PWM video data signals) combined with PWMF1 signals (selectedimage mode) by the PWM IC (IC208); they are then sent to the laser driver PCB of thelaser scanner as two sets of laser drive signals (BDATA*, BDATA) by way of the LVDS IC(IC209).When making full-color copies, the foregoing operations are performed for Y, M, C,and BK in sequence to form images. When making mono-color copies, on the other hand,these operations are performed for one of the four colors.At the end, the laser driver PCB is ready to send the laser drive signals (DATA*; resultof demodulation by the receiver (IC1001) to the laser drive IC (IC1002).*1 Reader controller PCB (when making copies with the reader unit installed).Note:Switching the Image ModeThe printer unit switches image mode (text or halftone) in response to the image modeswitch command from the reader controller PCB so as to enable the best images intext and halftone areas.CHAPTER 3 LASER EXPOSURE SYSTEM3-5Download free service manual at http://printer1.blogspot.com
