Canon CANOSCAN N1220U Service Manual

Also see for CANOSCAN N1220U: User guide User guide Getting started guide Getting started

CHAPTER 22 - 6 COPYRIGHT  2000 CANON INC. CANOSCAN N650U/N656U/N1220U REV.0 JUNE 2000 PRINTED IN JAPAN (IMPRIME AU JAPON)Figure 2-5When the hardware setting, home position detection and border detection between blackand white have completed, the scanner is on standby to wait for a command from the hostcomputer.Document glass (rear side) White mark areaBlack mark areaWhen the scanner is powered ON, it performs hardware setting, home position detection, andborder detection between black and white according to the flowchart shown in Figure 2-4.1) Hardware settingGate array and buffer RAM in the main PCB are checked if they function normally.2) Home position detection/Border detection between black and whiteThe scanner detects the home position by the home position sensor by using a black markarea and white mark area in the rear of the document glass.Firstly the home position sensor defines the home position, where the scanning unit reads ablack mark area.Secondly, the border between a white mark area and black mark area is detected. Thescanning unit moves forward reading image signals with the LED of the contact image sensorturned ON. When the scanning unit has reached the white mark area, and the peak value of thelight intensity to the scanning unit has reached a white level, the scanning unit stops to definethere as the border between a black mark area and white mark area. The number of steps of thedrive motor is calculated to define the distance from the home position to the white mark area.