Canon LBP-860 Service Manual page 49

CHAPTER 2
3. laser diode emission control
Laser diode emission is controlled by VIDEO
signal (/VDOJ, which is sent from the video
controller and processes the paper size data.
The paper size data is input to the CPU
from the cassette size sensing switches for
cassette feed and by the paper size
command from the video controller for
multi-purpose tray feed.
The CPU (IC201) transfers the /VDO
signal from the video controller to the laser
driver as it is as the /VDATA signal
The CPU sends data to the gate array
AND BOTTOM ERASE signal [TOPE) and
H O R I Z O N T A L M A S K s i g n a l
according to the paper size data from
and not output externally.)
To prevent the laser beam from writing
on the non-image area during the non-
unblinking period, IC202 makes the
only when the TOPE and MSK signals are
when the /ENBL signal is "L" and the
The gate array (IC202) generates the
UNBLINKING signal (UBL) according to the
BD INPUT signal [/BDI) sent from the BD
PCB in the laser/scanner unit. IC202 sets
t h e U B L s i g n a l l o "H" d u r i n g t h e
unblinking period and sets the FORCIBLE
LASER ON signal (/LON). The laser driver
switches the laser diode ON when the
2 - 1 2
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M S K -Tlr
Figure 2-13
Notes: 1.
laser beam writes on the drum.
2.
The duration of Tl & T2 vary
according to paper size. When
using the multi-purpose tray
the printer cannot comprehend
the width of the paper when the
p a p e r s i z e h a s n o t b e e n
s p e c i f i e d b y a p a p e r s i z e
c o m m a n d f r o m t h e v i d e o
c o n t r o l l e r . Tl i s t h e r e f o r e
specified as legal size paper
(maximum printable width).