| 摘要 |
A bar code scanner includes aseparate transmitter and receiver, each being able to ultrasonically transmit and receive data, respectively. The receiver transmits an acknowledgement signal when a protocol is received, and sends the acknowledgement signal to the transmitter which, unless it receives the acknowledgement signal, will retransmit the protocol a predetermined number of times. The transmitter includes a receiver which monitors an ultrasonic frequency band for a time period in which transmission by the transmitter is not allowed. The time period corresponds to a time when another ultrasonic signal in the ultrasonic frequency band is detected by the receiver of the transmitter. Transmission by the transmitter is allowed as soon as the another ultrasonic signal is no longer detected by the receiver of the transmitter.
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