Xerox Phaser 6121MFP Service Manual page 64

Theory of Operation
Laser Write Timing
2-22
When a Ready signal is detected after the print cycle begins, a Laser On signal is
output from the Engine Control Board. The Laser On signal triggers each laser
diode illuminating the SOS Board and generating an SOS signal. The SOS signal is
used to synchronize the timing at which the laser write each scan line.
The print start position in the CD direction is determined by the CD Print Start
signal (/HSYNC) that is output from the Image Processor Board and the width of
the paper.
The print start position in the FD direction is determined by the Image Write Start
signal (TOD) that is output from the Image Processor Board and the length of the
paper. The laser emission area is determined by the paper size. The area of 4 mm
on both the leading and trailing edges of the paper is, however, the void image
area.
/HSYNC
/VIDEO
4 mm
4 mm
4 mm
/VIDEO /TOD
4 mm
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Phaser 6121MFP Service Manual