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149 lines
3.2 KiB
149 lines
3.2 KiB
18 years ago
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<title> Flow Control </title>
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<h1 align="center">Flow Control</h1>
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<!--INDEX "Flow control" dlproto dlecho Xon-Xoff Etx-Ack -->
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A flow-control protocol is selected to ensure that the host does not
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send data too fast for the target to receive. The need for this can
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arise because, although the target system may be able to read a record
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at 9600 baud, the target system may need time to process that record
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before it can read the next record.<p>
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The environment variables dlproto and dlecho are used specify the
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flow-control protocol.<p>
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The following table summarizes the four flow-control protocols supported by
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this <a href="mondef.htm">Monitor</a>.<p>
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<table border cellpadding="5" width="95%">
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<tr bgcolor="#CCCCFF">
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<th>Terminal Emulator Sends</th>
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<th>Target Returns</th>
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<th>Set</th>
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<th>Application</th>
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</tr>
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<tr bgcolor="#CCCCCC">
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<td valign="top"> Line terminated by carriage return</td>
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<td valign="top">Echoes same line</td>
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<td valign="top" nowrap><tt> dlecho = on<br>
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dlproto = none<tt></tt></tt></td>
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<td valign="top"> Terminal Emulator waits for full line to be echoed before
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sending next line. </td>
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</tr>
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<tr>
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<td valign="top"> Line terminated by carriage return</td>
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<td valign="top">Returns line-feed character</td>
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<td valign="top" nowrap><tt>
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dlecho = lfeed<br>
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dlproto = none<tt></tt></tt></td>
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<td valign="top">
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Terminal Emulator waits for line-feed to be echoed before sending next line.
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</td>
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</tr>
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<tr bgcolor="#CCCCCC">
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<td valign="top"> Line terminated by carriage return</td>
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<td valign="top">Returns Xoff and Xon characters</td>
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<td valign="top" nowrap><tt> dlecho = off<br>
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dlproto = XonXoff<tt></tt></tt></td>
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<td valign="top"> Terminal Emulator sends until Xoff. Resumes sending after
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Xon. </td>
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</tr>
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<tr>
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<td valign="top"> Line terminated by ETX character</td>
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<td valign="top">Returns Ack character</td>
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<td valign="top" nowrap><tt>
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dlecho = off<br>
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dlproto = EtxAck<tt></tt></tt></td>
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<td valign="top">
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Terminal Emulator sends line terminated by Etx. Sends next line after Ack
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(see note).
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</td>
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</tr>
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</table>
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<p> <b>Note:</b> The Xon-Xoff protocol is often not as reliable a method of flow-control
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as it might first appear. This is because many host systems do not shut off
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the flow of characters immediately upon receiving an Xoff. They may continue
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to transmit 20 or 30 bytes before finally stopping. Unfortunately these characters
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will not be seen by the monitor because it is not interrupt driven, and will
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be busy processing the previous line.
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<h2>See Also:</h2>
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<blockquote>
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<p><a href="c_stty.htm">stty</a>, <a href="htermhlp.htm">hyper term help</a>,
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<a href="terms.htm">terminals</a> and <a href="tiphelp.htm">Unix tip help</a></p>
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</blockquote>
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<p>
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<p><hr>
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<p><b>Navigation:</b> <a href="pmon.htm">Document Home</a> | <a href="doctoc.htm">Document
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Contents</a> | <a href="docindex.htm">Document Index</a></p>
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<p><!--$Id: flwctl.htm,v 1.1.1.1 2006/09/14 01:59:06 root Exp $ --> </p>
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<p>
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<p>
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<p>
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<p>
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