Canon LBP-1000 Service Manual page 68

CHAPTER 2
The paper reaches the registration roller after its skew is corrected by hitting the registration
shutter.
The engine controller sends the /BD signal to the video controller in a specified period of time
after the top-of-page sensor (PS502) detects the leading edge of the paper. The /BD signal of
this printer functions as both VERTICAL SYNC and HORIZONTAL SYNC signals, and is output
to the video controller for a period of time corresponding to the paper length.
As the paper is fed during this time, the leading edge of the image on the drum matches the
leading edge of the paper by sending the /VDO and VDO signals in a specified period of time
after the video controller receives the /BD signal. The paper is sent to the fixing/delivery unit
after transfer and separation process.
There are two photointerrupters (PS502, PS503) on the paper path for detecting arrival or
passing of the paper.
The CPU assesses a paper jam and reports it to the video controller if the paper does not
arrive or pass through the sensors within a specified period of time.
As this printer has no paper size detection mechanism, the size of the paper set on the pick-
up sources cannot be detected.
The printer detects the paper size by measuring the time from the top of paper sensor (PS502)
detects the leading edge of the paper until the trailing edge of the paper clears the sensor. The
CPU assesses a paper size mismatch and reports it to the video controller, if the detected paper
size differs from the paper size specified by the video controller.
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