Canon CANOSCAN FB330 series Service Manual page 49

When CanoScan FB630U/FB636U is powered ON, it performs hardware setting, home position
detection, and USB transmission speed measurement according to the flowchart shown in Figure
2-10.
1) Hardware setting
Gate array and buffer RAM in the main PCB are checked if they function normally.
2) Home position detection
The scanner detects home position by the home position sensor on the button PCB. The home
position is in a black mark area. Then the scanner moves the scanning unit forward reading
image signals with the LED of the contact image sensor turned ON to detect the border between a
black mark area and white mark area. When the scanning unit has reached the white mark area,
and the peak value of the light intensity to the scanning unit has reached a white level, the
scanner stops the scanning unit to define there as the border between a black mark area and
white mark area. The number of steps of the scanning unit drive motor is calculated to define the
distance from the home position to the white mark area.
3) USB transmission speed measurement
The scanner has 2 operation clocks for driving the contact image sensor, the operation clock is
selected by the operation speed of the host computer. The scanner sends the data to the host
computer to measure the USB transmission speed to define the operation clock for the contact
image sensor.
When the hardware setting, home position detection and USB transmission speed
measurement have completed, the scanner is on standby to wait for a command from the host
computer.
COPYRIGHT © 1999 CANON INC. CANOSCAN FB330/FB630 SERIES REV.0 OCT. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
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