Canon CANOSCAN FB330 series Service Manual page 39

When CanoScan FB330P/FB630P is powered ON, the CPU in the main PCB performs
hardware setting and home position detection according to the flowchart shown in Figure 2-6.
1) Hardware setting
The CPU, gate array, and buffer RAM in the main PCB are checked if they function normally.
Also default setting of timer and communication processing of the gate array are performed.
For CanoScan FB330P/FB630P, overvoltage detection is also performed to check if an AC
adapter for other scanners is connected and overvoltage is input.
The CPU is input with an AC adapter divided voltage, and starts to check the AC adapter input
voltage when the hardware setting in the power ON sequence has completed, then keeps on
checking during standby.
When the CPU judges an overvoltage beyond preset level is input, it stops all processing except
for the communication with the host computer and sends an overvoltage detection error to the
host computer.
2) Home position detection
The CPU detects the home position by detecting a black area and the border between black
and white, using a black mark area and white mark area on the back of the document glass.
Document glass (back side)
The CPU moves the scanning unit backward reading image signals to detect a black area.
When the black area is detected, the CPU stops the scanning unit.
The CPU moves the scanning unit forward reading image signals with green LED turned ON to
detect the border between black and white. When the scanning unit reaches the white mark area
and the peak value of the light intensity to the scanning unit reaches white level, the CPU stops
the scanning unit. If not all pixels in the vertical scanning direction are white, the CPU moves
the scanning unit forward up to 2 mm until all pixels in the vertical scanning direction are white,
where the CPU defines as the home position.
When the hardware setting and home position detection 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)
Black mark area
White mark area
Figure 2-7
CHAPTER 2
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