Canon LBP-1210 Service Manual page 117

sample mode (in which the APC is performed), forcing the LD to emit.
The intensity of the LD is detected by the photo diode (PD) and fed back to the sample hold
circuit through the comparator.
The laser drive IC controls the output current of the drive circuit to bring the fed-back laser
intensity to its target value set in the IC.
When both the CNT0 and CNT1 are set "H", the LD is forcibly turned OFF and the sample
hold circuit enters the hold mode (in which an image is masked). The laser driver IC converts
the controlled laser intensity into voltage and writes it to C803.
3. Image masking control
This control forbids laser beam emission in the non-image area other than the unblanking peri-
od.
When the CNT0 and CNT1 signals sent from the CPU are set "H", the laser driver IC forcibly
turns OFF the laser diode (LD), and the sample hold circuit in the laser drive IC enters hold
mode. This is referred to as an image masking state. During this state, the LD does not emit
regardless of the VIDEO (/VDO, VDO) signals output from the interface controller.
Unmasking area
Notes: 1. The shaded area indicates the area where the laser beam can write.
2. T1 is the range 1mm toward the center from the right and left sides of the Letter size
regardless of the paper size specification.
3. T2 is the range 1mm from the leading edge of the paper (start of /BD output) to the
trailing edge. Note that if the number of /BD pulse lines (number of scan lines) is
specified by a command from the interface controller, the trailing edge will be where
the /BD output for the specified number of the scan lines completes. In case that
the number of the scan lines is not specified, the trailing edge will be where the paper
top sensor (PS402) detects a paper-out.
/BD
1 mm
Figure 2-4-3
T1
1 mm
CHAPTER 2
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