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<p><b>TI-73 Link Protocol Guide v1.0</b> - Packet formats</p>
<center>
<h2>
<hr align="center"> Packet Formats</h2>
</center>
<p>Texas Instruments calculators always send data and responses in
self-contained "packets."<br>
Packets have the following format:<br>
<i>Note - all 2-byte integers are transmitted little-endian Intel-style
(least significant byte first).</i></p>
<p>
<table border="1" cellspacing="0" width="92%">
	<tbody>
    <tr>
		<th width="7%" bgcolor="#008800"><font color="#ffffff">Offset</font></th>
		<th width="8%" bgcolor="#008800"><font color="#ffffff">Length</font></th>
		<th width="85%" bgcolor="#008800"><font color="#ffffff">Description</font></th>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">0</td>
		<td width="8%" bgcolor="#ffffff">1 byte</td>
		<td width="85%" bgcolor="#ffffff">Machine ID byte</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">1</td>
		<td width="8%" bgcolor="#ffffff">1 byte</td>
		<td width="85%" bgcolor="#ffffff">Command ID byte</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">2</td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		<td width="85%" bgcolor="#ffffff">Length of data (see note below)</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">4</td>
		<td width="8%" bgcolor="#ffffff"><i>n</i> bytes</td>
		<td width="85%" bgcolor="#ffffff">Data (if attached)</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">4+<i>n</i></td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		<td width="85%" bgcolor="#ffffff">Checksum (if data is attached)</td>
	</tr>
  </tbody>
</table>
<i>Note - The "Length of data" element may not be equal to zero if the
packet contains no data. In this case, the Command ID byte will
indicate that the packet contains no data.</i></p>
<p></p>
<h4>The Machine ID Byte</h4>
<p>The Machine ID byte identifies the machine that is sending the
packet. It can have one of the following values:
<table border="1" cellspacing="0" width="66%">
  <tbody>
    <tr>
      <th width="13%" bgcolor="#dddddd">Value</th>
      <th bgcolor="#dddddd">Description</th>
    </tr>
    <tr>
      <td width="13%">07h</td>
      <td>Computer sending TI-73 data</td>
    </tr>
    <tr>
      <td width="13%">74h</td>
      <td>TI-73</td>
    </tr>
  </tbody>
</table>
</p>
<p></p>
<h4>The Command ID Byte</h4>
<p>The Command ID byte identifies the request or response that the
machine is sending. It can have one of the following values:</p>
<p>
<table border="1" cellspacing="0" width="66%">
	<tbody>
    <tr>
		<th width="22%" bgcolor="#dddddd">Value</th>
		<th width="259" bgcolor="#dddddd">Description</th>
		<th bgcolor="#dddddd">Data Included</th>
	</tr>
	<tr>
		<td width="22%">06h</td>
		<td width="259">Variable Header (VAR)</td>
		 <td>A fixed-length, NUL padded <a href="#varheader">variable
header</a></td>
	</tr>
	<tr>
		<td width="22%">09h</td>
		<td width="259">Clear to send (CTS)</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">15h</td>
		<td width="259">Data packet (DATA)</td>
		<td>Screenshot/variable/backup data</td>
	</tr>
	<tr>
		<td width="22%">36h</td>
		<td width="259">Skip/Exit (SKIP/EXIT)</td>
		<td>A one-byte rejection code (see codes below)</td>
	</tr>
	<tr>
		<td width="22%">56h</td>
		<td width="259">Acknowledge (ACK)</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">5Ah</td>
		<td width="259">Checksum Error (ERR)<br>
			The previous packet must be sent again.</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">68h</td>
		<td width="259">Check ready (RDY)</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">6Dh</td>
		<td width="259"><i>Silent</i> - Request Screenshot (SCR)</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">92h</td>
		<td width="259">End of Transmission (EOT)</td>
		<td><i>None</i></td>
	</tr>
	<tr>
		<td width="22%">A2h</td>
		<td width="259"><i>Silent</i> - Request Variable (REQ)</td>
		 <td>A fixed-length, NUL padded <a href="#varheader">variable
header</a></td>
	</tr>
	<tr>
		<td width="22%">C9h</td>
		<td width="259"><i>Silent</i> - Request to Send Variable (RTS)</td>
		 <td>A fixed-length, NUL padded <a href="#varheader">variable
header</a></td>
	</tr>
  </tbody>
</table>
</p>
<p></p>
<p>Rejection codes (used with Command ID 36h) can have one of the
following values:</p>
<p>
<table border="1" cellspacing="0" width="66%">
	<tbody>
    <tr>
		<th width="13%" bgcolor="#dddddd">Value</th>
		<th bgcolor="#dddddd">Description</th>
	</tr>
	<tr>
		<td width="13%">01h</td>
		<td>EXIT - The entire transmission has been cancelled.</td>
	</tr>
	<tr>
		<td width="13%">02h</td>
		<td>SKIP - The current variable has been skipped.</td>
	</tr>
	<tr>
		<td width="13%">03h</td>
		<td>OUT OF MEMORY (silent transmissions only) - The receiving
calculator is out of memory.</td>
	</tr>
  </tbody>
</table>
</p>
<p></p>
<h4>The Checksum</h4>
<p>The checksum is a 16-bit value used to verify the integrity of the
data in the packet. It only present if data is present.<br>
The checksum is calculated by taking the lower 16 bits of the sum of
the data bytes, as shown below:</p>
<pre>int calculateChecksum(unsigned char* data, unsigned short datalength) {<br>   unsigned short x, checksum;<br>   for(x=0; x&lt;datalength; x++) {<br>      checksum+=data[x];  //overflow automatically limits to 16 bits<br>   }<br>   return checksum;<br>}</pre>
<center>
<h3>
<hr align="center"> <a name="varheader"></a>Variable Headers</h3>
</center>
<p>A Variable header contains information about one variable in the
calculator.<br>
<table border="1" cellspacing="0" width="92%">
  <tbody>
    <tr>
      <th width="7%" bgcolor="#008800"><font color="#ffffff">Offset</font></th>
      <th width="8%" bgcolor="#008800"><font color="#ffffff">Length</font></th>
      <th width="85%" bgcolor="#008800"><font color="#ffffff">Description</font></th>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">0</td>
      <td width="8%" bgcolor="#ffffff">2 bytes</td>
      <td width="85%" bgcolor="#ffffff">Size of actual variable data,
in bytes</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">2</td>
      <td width="8%" bgcolor="#ffffff">1 byte</td>
      <td width="85%" bgcolor="#ffffff">Type ID Byte (see type ID's
below)</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">3</td>
      <td width="8%" bgcolor="#ffffff">8 bytes</td>
      <td width="85%" bgcolor="#ffffff">Variable name, padded on the
right with       NULL characters (0h). This field is always tokenized.
Not used for ID list.<i></i></td>
    </tr>
  </tbody>
</table>
<i>Note: These bytes only make up the "data" section of the packet.<br>
</i><i>Note2:<br>
</i><i> - for lists (L1..L6), the first token is a 5D byte followed by
another byte:   01 for L1 to 06 for L6.</i><br>
</p>
<p></p>
<h4><a name="vartypes"></a>The Type ID Byte</h4>
<p>The type ID byte specifies the type of variable that is being
transmitted. It can have one of the following values:</p>
<p>
<table border="1" cellspacing="0" width="66%">
  <tbody>
    <tr>
      <th width="13%" bgcolor="#dddddd">Value</th>
      <th bgcolor="#dddddd">Description (click for variable format)</th>
    </tr>
    <tr>
      <td width="13%">00h</td>
      <td><a href="vars.html#real">Real Number</a></td>
    </tr>
    <tr>
      <td width="13%">01h</td>
      <td><a href="vars.html#list">Real List</a></td>
    </tr>
    <tr>
      <td width="13%">02h</td>
      <td><a href="vars.html#equation">Y-Variable</a></td>
    </tr>
    <tr>
      <td width="13%">05h</td>
      <td><a href="vars.html#program">Program</a></td>
    </tr>
    <tr>
      <td width="13%">06h</td>
      <td>Assembly <a href="vars.html#program">Program</a> ?</td>
    </tr>
    <tr>
      <td width="13%">07h</td>
      <td><a href="vars.html#picture">Picture</a></td>
    </tr>
    <tr>
      <td width="13%">0Bh</td>
      <td><a href="vars.html#window">Window Settings</a><i> (See note
below)</i></td>
    </tr>
    <tr>
      <td width="13%">0Fh</td>
      <td><a href="vars.html#window">Window Settings</a><i> (See note
below)</i></td>
    </tr>
    <tr>
      <td width="13%">11h</td>
      <td><a href="vars.html#table">Table Setup</a><i> (See note below)</i></td>
    </tr>
    <tr>
      <td width="13%">13h</td>
      <td><a href="backup.html">Backup</a></td>
    </tr>
    <tr>
      <td width="13%">19h</td>
      <td><a name="19h"></a><a href="silent.html">Directory</a> <i>(See
note below) </i>- only used when requesting a directory</td>
    </tr>
    <tr>
      <td width="13%">23h</td>
      <td><a name="19h"></a><a href="flash.html">FLASH</a> Operating
System</td>
    </tr>
    <tr>
      <td width="13%">24h</td>
      <td><a name="19h"></a><a href="flash.html">FLASH</a> Application</td>
    </tr>
    <tr>
      <td width="13%">26h</td>
      <td><a name="FLASH"></a><a href="flash.html">ID list</a></td>
    </tr>
    <tr>
      <td width="13%">27h</td>
      <td><a name="19h"></a><a href="flash.html">Get Certificate</a></td>
    </tr>
  </tbody>
</table>
</p>
<p></p>
<h4><a name="backup"></a>Backup Header Format</h4>
<p>If the type ID byte specifies a backup, the variable header takes
the following   9-byte format :</p>
<p>
<table border="1" cellspacing="0" width="92%">
	<tbody>
    <tr>
		<th width="7%" bgcolor="#008800"><font color="#ffffff">Offset</font></th>
		<th width="8%" bgcolor="#008800"><font color="#ffffff">Length</font></th>
		<th width="85%" bgcolor="#008800"><font color="#ffffff">Description</font></th>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">0</td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		 <td width="85%" bgcolor="#ffffff">Size of first backup section
(flags area),       in bytes</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">2</td>
		<td width="8%" bgcolor="#ffffff">1 byte</td>
		 <td width="85%" bgcolor="#ffffff">Type ID Byte (13h in this
case)</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">3</td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		 <td width="85%" bgcolor="#ffffff">Size of second backup section
(data area),       in bytes</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">5</td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		 <td width="85%" bgcolor="#ffffff">Size of third backup section
(symbol area),       in bytes</td>
	</tr>
	<tr>
		<td width="7%" bgcolor="#ffffff">7</td>
		<td width="8%" bgcolor="#ffffff">2 bytes</td>
		 <td width="85%" bgcolor="#ffffff">Start User Area Address</td>
	</tr>
  </tbody>
</table>
</p>
<h4><a name="FLASH"></a>FLASH Header Format<br>
</h4>
<p>If the type ID byte is in the range 22...28h, the variable header
takes the   following 10-byte format : </p>
<table border="1" cellspacing="0" width="92%">
  <tbody>
    <tr>
      <th width="7%" bgcolor="#008800"><font color="#ffffff">Offset</font></th>
      <th width="8%" bgcolor="#008800"><font color="#ffffff">Length</font></th>
      <th width="85%" bgcolor="#008800"><font color="#ffffff">Description</font></th>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">0</td>
      <td width="8%" bgcolor="#ffffff">2 bytes</td>
      <td width="85%" bgcolor="#ffffff">Size of actual data, in bytes
(LSB).</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">2</td>
      <td width="8%" bgcolor="#ffffff">1 byte</td>
      <td width="85%" bgcolor="#ffffff">Type ID Byte (see type ID's
below)</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">3</td>
      <td width="8%" bgcolor="#ffffff">2 bytes</td>
      <td width="85%" bgcolor="#ffffff">Size of actual data, in bytes
(MSB).</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">5</td>
      <td width="8%" bgcolor="#ffffff">1 byte</td>
      <td width="85%" bgcolor="#ffffff">Flag - Always has a value of 0h
but bit       7 is set if archived.</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">6</td>
      <td width="8%" bgcolor="#ffffff">2 bytes</td>
      <td width="85%" bgcolor="#ffffff">FLASH offset</td>
    </tr>
    <tr>
      <td width="7%" bgcolor="#ffffff">8</td>
      <td width="8%" bgcolor="#ffffff">2 bytes</td>
      <td width="85%" bgcolor="#ffffff">FLASH page</td>
    </tr>
  </tbody>
</table>
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<hr align="center"> <i>Site maintained by Romain Li&eacute;vin (</i><a
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