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Appendix C Keyboard
Compaq Personal Computers
Changed - November 1996
C-14
COM Port
(System Unit)
Analog
Video
Data
Motor Cntrl.
Serial Data
Clocks & LED
Cntrl.
Digital Video Data
24 VDC
Keyboard Unit
C.3 SCANNER DESCRIPTION
The scanner keyboard, available as an option, integrates a scanner with a SpaceSaver Windows
’95 keyboard, providing the ability to scan hardcopy looseleaf documents for faxing or electronic
storage. The scanner provides resolutions up to 400 dpi and 256 shades of gray and outputs
through a standard serial interface to the system unit. Using optical character recognition (OCR)
support software, printed textual data can be converted into editable files.
Operation of the scanner starts automatically when a sheet is inserted into the Contact Image
Sensor (CIS). A button on the left side of the keyboard allows then operator to open a menu, halt
scanning in progress, or invoke a serial port test. Figure C-9 shows a block diagram of the key
scanner elements.
Figure C–9.
Scanner Elements, Block Diagram
The Contact Image Sensor (CIS) and paper drive unit handles the hardcopy input. As each sheet
is placed into the input slot, the sheet activates the mechanism and is drawn through and scanned
by an LED illumination/photodiode sensor array. The drive motor provides 96 steps per
revolution (3.75 degress per step) and is geared for 0.005 inch document movement per step for a
resolution of 200 dpi. Half-stepping provides 400 dpi vertical resolution.
An analog video data stream is developed and routed to the Digital-to-Analog (D/A) Processor
for conversion to digital video data that is routed to the Digital Processor. The Digital Processor
provides most of the control of the scanner operation. A 32-KB RAM provides storage of
executable code, pixel-to-pixel correction values, image processing line/diffusion data, and
transmission data buffering.
The scanner elements are powered from an external 24 VDC power supply. Internal components
use +5, +9, and -12 VDC.
Digital
Processor
CIS
and Paper Drive
M64290FP
Analog
Processor
32 KB
RAM
24 VDC
Power
Supply