Abstract: A dual channel video data recovery system for use in a bar code scanner. A first and a second video signal are generated in parallel in response to light reflected from a bar code. The first and second video signals are received and filtered to limit their frequency ranges and produce filtered first and second video signals. The first and second filtered video signals are limited to different and preferably coverlapping frequency ranges. The first and second video signals have differing thresholds which may be dynamically varied. The first and second filtered video signals are converted to first and second digital data strings. If both strings contain useful data, the string containing the higher-quality data is decoded to recover bar code information. If only one string contains useful data, the string containing useful data is decoded.

Abstract: The useful life of a laser, such as a laser diode, is extended by causing the laser to operate only intermittently when continuous operation is not required. When such a laser diode is used in a scanner for scanning coded symbols, such as bar codes, in merchandise check-out operations, continuous operation is required only when a coded symbol is present in a target area. A sensing device is provided for sensing the transitions in light reflected back from the target area, and a counter is provided for counting the number of such transitions. Since a much larger number of transitions are sensed and counted when a coded symbol is being read than when no such symbol is present in the target area, this difference in number of transitions is used to distinguish between the two conditions and to cause the laser diode to be turned on for continuous operation only when a coded symbol is present in the target area to be read.

Abstract: A scanning device having a laser, a motor for driving a mirror arrangement for moving the beam of the laser, and a microprocessor for control purposes is provided with a system for measuring and correcting fault conditions to meet laser safety requirements. Detection devices are provided for determining whether the laser is on or off, and whether the motor is running at or above a predetermined speed. If the laser is stuck in an on condition, then the motor is left running and an error is signalled. If the motor will not operate at or above the minimum speed, the laser is maintained in an off condition and an error is signalled.

Abstract: A communication interface for controlling the transfer of data between a host processor configured to process data of a first length and a remote storage member configured to store data of a second length includes a bus controller for transferring data between the interface and the remote storage member, a data transfer member for controlling the transfer of data between the host processor and the interface, and a control processor for controlling operating of the bus controller and the transfer member. A first storage member stores data words of said second length and sequentially outputs the data words over a communication bus to the host processor configured to transmit data words of said first length. A second storage member stores data representing the operating status of the transfer member and the bus controller, enabling the control processor to monitor the status of the transfer member and the bus controller.

Abstract: A digital timing recovery circuit is disclosed for synchronously transmitting digitally encoded data in a multiterminal configuration between a data processor and a plurality of data terminals associated therewith. Phase shifted synchronous data from the data processor is continuously compared with a newly generated synchronous clock generated at a repeater interposed along the communication line for minimization of the time differential between the retiming clock and the transmitted data. The data transitions enable a digitally implemented one-shot, which generates pulses, the leading edges of which pulses enable a difference counter, while the leading edges of the retiming clock pulses disable the counter. The difference counter output is sampled in a digital phase locked loop to derive the number of cycles of a stable oscillator which occur between the two aforementioned leading edges of the generated pulses.

Abstract: A data communication system for asynchronously transmitting intermittently generated digitally encoded data between a data processor and a plurality of data terminals associated therewith is disclosed wherein the allowable communications line distance between the data processor and the terminals is substantially increased. Asynchronous data from the terminals is intercepted by a novel repeater, retimed in accordance with a newly generated retiming clock to eliminate bit-shift or other errors from the data, and retransmitted to the central processor over an extended length transmission line, with the repeater being substantially transparent to the flow of data. Decoding of an appropriate code by the repeater which is indicative of the receipt of a data character causes the switching from a data derived clock to a retiming clock for reencoding and retransmission of the data.