Partner SD-730N, Руководство по программированию

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Introduction 47
Introduction
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Handshaking
Protocol controls data flow between the scanner and a serial host
computer.
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Disable: The communication way only actives the TXD (transmit data)
and RXD (receive data) without regard for any hardware (RTS/CTS) or
software (XON/XOFF or ACK/NAK) handshaking protocol.
„
RTS/CTS (CTS/RTS): When this option is selected the RTS (request
to send) and CTS (clear to send) signal will be issued before normal data
communication. For example, if the scanner wants to send the barcode
data to host computer, it will issue the RTS (CTS) signal first, wait for the
CTS (RTS) signal from the host computer, and then perform the normal
data communication. If there is no replied CTS (RTS) signal from the host
computer after the time out duration (Response Delay Timer), the
scanner will issue warning 5 beeps.
„
Scanner Ready: The scanner will active the RTS signal upon power
on, and will transmit data upon receiving active CTS signals.
„
Data Ready: The scanner will active the RTS signal to indicate a
successful decoding and will transmit data upon receiving CTS signals.
„
STX/ETX: The STX (start of text) and ETX (end of text) are ASCII
codes whose values are 02H and 03H, respectively, and can be
preformed to pack together the normal data transmission.
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XON/XOFF: Controlled data flow is achieved between devices when
the receiving device sends ASCII XON/OFF codes whose values are
issued a Ctrl-S and Ctrl-Q to the transmitting device. In other words, when
the receiving device is unable to accept data, it sends an XOFF code to
inform the host to temporarily suspend data transmission.
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ACK/NAK: The ACK/NAK protocol provides a feedback to the serial
host computer that is programming the scanner. The ACK/NAK protocol
provides two vital functions. First, it provides the host with positive
acknowledgment that its commands are begin accepted and acted upon.
Second, and perhaps more important, it ensures that the host will not
issue commands to the scanner more quickly than the scanner can
process them. Whenever the scanner receives a correctly formatted
command, it sends a confirmation message followed by an ACK (06H)
code or receives an improperly formatted code; it sends a NAK (15H)
code.
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CTS Trigger: This operation enabled an external device to control
scanning. Applying an external trigger signal to the CTS input controls the
CTS trigger (with external triggering enable). When active, this signal
causes scanning to begin just as if the scanner’s trigger were depressed.
In the event of decoding, the trigger signal must be deactivated for a
minimum of 50 milliseconds before another scan can be attempted.