| 摘要 |
A lost scan line detecting device provides lost scan line information to a computer system which is connected to and which receives scan line picture data from a handheld scanner, thereby enabling the computer system to derive picture data which corresponds to a lost scan line from available scan line picture data. The handheld scanner generates a series of photo receiver pulses and a series of step trigger signals. Each of the photo receiver pulses is used to indicate that the handheld scanner has traveled by a distance which is equivalent to one scan line on a document being scanned. The handheld scanner generates each of the step trigger signals after one of the photo receiver pulses has been generated. The period between two step trigger signals is constant and corresponds to a predetermined maximum scanning speed of the handheld scanner. The lost scan line detecting device includes a first counter to count the photo receiver pulses and a second counter to count the step trigger signals. The count outputs of the first and second counters are compared, and a lost scan line signal is generated whenever the count outputs are unequal so as to indicate to the computer system that a lost scan line condition has occurred.
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